GIT high and low Flashcards

Question

6. What is the role of APC gene and what do mutations APC predispose to?

Answer 1

Familial adenomatous polyposis (FAP) -mutations in the tumour suppressor gene, adenopolyposis coli (APC) -APC degrades beta-catenin and inhibits cellular proliferation -adenomas require inactivation of both APC alleles, but mutates for “second” hit -autosomal dominant with near-complete penetrance of colonic manifestations (polyps) but incomplete penetrance of extra-colonic manifestations (retinal pigment)

Answer 2

**Protective Mechanisms in the Gut** - Non-immunological defence mechanisms represent an important line of intestinal defence in addition to humoral and cellular immunity, and include: - Microbiological defences (i.e., normal gut flora) - Physical defences - Chemical defences **Physical Defence Mechanisms** A single layer of intestinal epithelial cells (IECs) provides a physical barrier between the lamina propria (internal milieu) and the intestinal lumen, which contains normal gut flora and pathogens. **Physical Defences: Tight Junctions** - Intestinal epithelial cells are held together (cell-to-cell adhesion) by tight junctions, which form a seal against the external environment. - Primary barrier to the diffusion of solutes and traversal of pathogens through the intercellular space, creating a boundary between the apical and the basolateral plasma membrane domains. - Infection occurs only when a pathogen can colonize or cross through these barriers. - Tight junction: - ‘Kissing points’. - No intracellular space. - Adherens junction & Desmosomes: - Opposing membranes are 15-20 nm apart. **Physical Defences: Epithelial Cell Turnover and Peristalsis** - Intestinal epithelial cell (IEC) turnover is constant (every 4-5 days) and involves: 1. Shedding of cells damaged by microbial infection or stresses. 2. Replenishment by intestinal stem cells. - IEC turnover and peristalsis contractions help expel colonized pathogens and prevent overgrowth of normal gut flora. **Chemical Defence Mechanisms** - Often the first line of defence against infection. - Certain chemicals are produced by the host to protect against infections by GIT pathogens: - Bile: produced in liver, helps with digestion, antibacterial. - Enzymes: - Pepsin: produced in stomach, helps with digestion, antibacterial. - Trypsin/chymotrypsin/lipase: produced in pancreas, help with digestion, antibacterial. - Lysozyme: produced in upper intestinal tract, antibacterial. - Gastric acid: produced in stomach, helps with digestion antibacterial. - Mucus; viscous, antibacterial **Chemical Defences: Mucus** - Highly viscous, hydrophobic gel that covers mucosal surfaces and protects epithelial cells against chemical and microbial insult. For example: - Microbes coated in mucus may be prevented from adhering to the epithelium. - Mucus retains dimeric IgA to maximize exclusion of pathogens from gut epithelium - Mucin glycoproteins are a major component of mucus and responsible for the viscosity of the mucus layer. - Mucus layers range in thickness: 10 μm in the eye and trachea, 300 μm in the stomach, 700 μm in the intestine. - Mucus layer is not static but moves to clear trapped material. For example: - In GIT, the outer mucus layer is continually removed by peristalsis. **Chemical Defences: Mucus-Secreting Cells in the GIT** In the stomach: - Surface mucus cells (within gastric pit). - Neck mucus cells (within gastric gland). In the small and large intestine: - Brunner’s glands (within submucosa): - Localized to the duodenum. - Also produce alkaline fluids. - Goblet cells (within epithelium). **Chemical Defences: Gastric Mucus Layer** - HCl (acid) produced by parietal cells in the human stomach is concentrated enough to digest the stomach itself, yet gastric epithelium remains undamaged because it is acid-resistant. - Gastric mucus forms a protective layer over the gastric epithelium and acts as a diffusion barrier by secreting bicarbonate ions that remain trapped in the mucus gel, establishing a gradient: from pH 1-2 at the lumen, to pH 6-7 at the cell surface. **Chemical Defences: Intestinal Mucus Layer** - In the small intestine, the mucus forms a diffusion barrier containing antibacterial products that limit penetration by bacteria. - In the colon, bacteria are compartmentalized to the outer loose mucus layer; the inner mucus layer, which is attached to the epithelium, is almost free of bacteria and protects the epithelium (because outer layer has trapped microbes). **How Can Pathogens Overcome the Mucus Barrier?** - Several pathogens have developed mechanisms to subvert mucosal defensive measures, colonize the GIT, and cause infection. Examples include: - Helicobacter pylori (H. pylori) can swim through gastric mucus in the stomach and attach to epithelial cells beneath, where it can cause inflammation over the course of a lifelong infection. for more see [[Microbiology B5 - Lecture 2]] - Enterohaemorrhagic Escherichia coli (EHEC) produce proteins that specifically degrade mucin to gain access to the intestinal epithelium. - Defective mucus release, resulting in defective mucous layers and stagnation. **The Mucosal Immune System** - Immunological defence mechanisms represent an important line of intestinal defence in addition to non-immunological defence mechanisms that can be breached relatively easily. - These defence mechanisms are referred to as the mucosal immune system and are specifically adapted to generate a response to antigens encountered in: - Upper and lower respiratory tract. - Urogenital tract. - GIT. - And exocrine glands associated with these organs, e.g., pancreas, salivary glands, etc. - As such, the mucosal immune system forms the largest part of the human body’s immune tissue. **Location of Immune Cells in the GIT** - Lymphocytes (Bs, Ts) and other immune-system cells (e.g., macrophages, dendritic cells) are found throughout the GIT, in organized tissues, and scattered throughout the surface epithelium of the mucosa and lamina propria.

Answer 3

**Gut-Associated Lymphoid Tissue (GALT)** - Organized lymphoid tissues in the gut are known as the gut-associated lymphoid tissue (GALT), for example: - Peyer’s patches. - Solitary lymphoid follicles of the intestine. - Mesenteric lymph nodes. - Appendix. - Tonsils/adenoids **Peyer's Patches** - Found in the small intestine (rich within the ileum), see also [[Anatomy B5 - Lecture 2]]. - Consists of many B-cell follicles with germinal centers, and smaller T-cell areas. - Subepithelial dome (SED) is rich in dendritic cells, T cells, and B cells. - Overlying the lymphoid tissue and separating them from the gut lumen is a layer of follicle-associated epithelium containing: 1. Conventional intestinal epithelial cells (enterocytes). 2. Specialized epithelial cells (microfold or M cells). ---

Answer 4

- The dominant class of antibody in the mucosal immune system is (dimeric) IgA. - To generate an IgA-mediated response to antigen, naïve B cells are activated by antigen as IgM-producing B cells in Peyer's Patches and mesenteric lymph nodes, undergo isotype switching to IgA-producing B cells, and are then redistributed in the intestinal immune system. - Once in the lamina propria, plasma cells synthesize and secrete IgA into the subepithelial space. - To reach its target antigens in the gut lumen, IgA has to be transported across the epithelium, in a process known as transcytosis. --- **Translocation/Transcytosis of IgA** - Translocation of IgA across the IEC barrier is mediated through a process called transcytosis. - IgA dimers are secreted by plasma cells in the lamina propria and bind to the polymeric immunoglobulin receptor (pIgR) on the IEC **baso**lateral surface. - The IgA-pIgR complex is endocytosed and transported to the apical surface for release to the intestinal mucus layer and intestinal lumen. - Secreted IgA, together with the secretory component (SC; a proteolytic cleavage product of pIgR that remains associated with dimeric IgA), is known as secretory IgA (sIgA), which is important for neutralizing extracellular pathogens. --- **IgA Functions** *Murphy et al. (2008)* - secreted IgA on gut surface can bind and neutralise pathogens and toxins - IgA is able to bind and neutralise antigens internalised in endosomes - IgA can export toxins and pathogens from the lamina propria while being secreted i.e. opsonisation --- **CD4+ T Cell Response** - To generate a T cell response, naïve T cells must be activated and redistributed in the intestinal immune system. - Pathogens that penetrate the epithelium activate dendritic cells, to give strong co-stimulatory signals so that when they present antigen to naïve CD4 T cells in the lamina propria, effector TH1 and TH2 cells are generated to stimulate an active immune response. - CD4 TH1 cells produce macrophage-activating cytokines. - CD4 TH2 cells produce cytokines that stimulate B cells to produce antibodies. --- **CD8+ T Cell Response** - Peptides from invasive organisms bound to major histocompatibility complex (MHC) class I molecules on infected epithelial cells are recognized by intraepithelial lymphocytes (mainly CD8+ T cells loaded with antimicrobial proteins). - CD8+ T cells then release antimicrobial proteins/cytotoxic signs, inducing death of infected cells eg by perforin/granzyme, Fas/FasL pathways. ^[recall also against tumour cells]

Answer 5

--- **Mechanisms of Antigen Uptake** - Antigens present at mucosal surfaces must be transported across the epithelial barrier before they can stimulate the mucosal immune system. - The intestine has distinct routes and mechanisms of antigen uptake: - Uptake by Peyer's patches, mediated by M cells. - Direct uptake by dendritic cells. - Both routes lead to T cell activation. --- **Antigen Uptake by M-Cells** - Microfold cells (M cells) mediate the transport of luminal antigens and bacteria across the epithelial barrier (transcytosis). - M cells are localized to Peyer's Patch lymphoid tissue. - Antigens that are transported across the epithelial barrier are taken up by dendritic cells within Peyer's Patches to facilitate antigen presentation to naïve T cells. --- **Antigen Uptake by Dendritic Cells** - Dendritic cells can extend processes across the epithelial layer to capture antigen from the lumen of the gut. - This allows dendritic cells to acquire antigens across the intact epithelial barrier without the need for M cells. - After antigen uptake, dendritic cells transport them to T cell areas eg Peyers, patches, or mesenteric lymph nodes via lymphatics that drain the intestinal wall.

Answer 6

**Control of the Immune Response** - The majority of antigens encountered by the intestinal immune system are not derived from pathogens, but come from food and normal gut flora. - As such, the intestinal immune system has evolved means to distinguish harmful pathogens from antigens in food and natural gut flora by: - Producing strong effector responses to pathogens. - Remaining unresponsive to foods and commensals. --- **Is the Normal Flora Ignored?** - Generally normal flora are unable to penetrate the epithelium - The inability of normal flora to penetrate the epithelium as well as the downregulation of TLRs/NODs on the apical surface of epithelial cells means that they have a reduced ability to induce a localized epithelial cell-mediated inflammatory response. - Even after their direct uptake by dendritic cells, there is production of TGF-β, thymic stromal lymphopoietin (TSLP), and prostaglandin E2 (PGE2) by gut epithelial cells, which maintain dendritic cells in a quiet state with low levels of co-stimulatory molecules, producing TH3 and Treg cells, which have a more immunomodulatory function. - However, **lack of tolerance** to these bacteria in the **systemic immune system** means that **it will be able to generate protective immunity to them if they do enter other parts of the body and bloodstream. --- **Does the Normal Flora Overcome Immune Tolerance?** YES. For example: - Massive influx of commensal bacteria overcomes these homeostatic mechanisms, resulting in full activation of the immune response eg C difficile (See [[Microbiology B5 - Lecture 1]], [[Microbiology B5 - Lecture 4]]). - Or if regulatory mechanisms fail, unrestricted immune responses to normal flora can lead to inflammatory bowel diseases. **Immunological Tolerance to Food** - Food is not digested completely in the intestine, with significant amounts being absorbed into the body. - Absorbed food is then taken up by mucosal dendritic cells that give weak co-stimulatory signals so that when they present antigen to naïve CD4 T cells, anti-inflammatory (TH3) or regulatory T cells (Treg) are generated. - CD4+ TH3 cells produce transforming growth factor-beta (TGF-β) that has many immunosuppressive properties. - CD4+ Treg cells produce the anti-inflammatory cytokine interleukin-10 (IL-10). - This lack of an inflammatory response in the intestine induces an active form of immunotolerance characterized by a state of long-lasting and antigen-specific unresponsiveness. - Breakdown of immunotolerance is believed to occur in celiac disease, where effector T cells generate a response against gluten found in wheat, resulting in inflammation that destroys the upper small intestine. ^[see also [[Gastroenterology - Lecture 1]]]

Answer 7

GI manifestations * Vomiting * Abdominal bloating * Abdominal pain * Variable bowel habit (both loose bowel motions and constipation) * steatorrhea * Iron deficiency anaemia

Answer 8

on-GI manifestations * Lethargy, weakness * Altered bowel habit * Failure to thrive * Recurrent or persistent iron deficiency anaemia * Dental enamel defects * Low vitamin D * Delayed puberty and infertility * Aphthous ulcers * Raised transaminases * Dermatitis herpetiformis

Answer 9

Pathogenesis * Usually responds to strict exclusion of gluten * Requires a specific genetic background (HLA DQ2 or HLA DQ8) * Patients have circulating IgA autoantibodies to tissue transglutaminase (tTG) a ubiquitous enzyme that catalyses deamination from a glutamine to lysine residue - increases afffinity for HLA * 30-50% amino acids in gluten are glutamine * A 33 amino acid peptide from alpha-2 gliadin, the main fraction of gluten binds to HLA class II DQ2 > DQ8 * These class II antigens loaded with peptide stimulate antigen-specific CD4 T cells and trigger an inflammatory response and antibodies directed against tTG * Only 1/50 of those who are HLA DQ2 or DQ8 positive develop coeliac disease with other genetic and/or environmental factors contributing to development of the disease * A number of non-HLA genes identified as conferring predisposition to coeliac disease * Diarrhoea related to villous atrophy i.e. flattening in the small intestine resulting in mucosal malabsorption (steatorrhoea) and lactase deficiency, fluid hypersecretion from crypt epithelia secondary to crypt hyperplasia v ### Histology and pathology * Macroscopic clues on endoscopy * loss of folds, modularity, fissuring * Multiple biopsies of the duodenum required * duodenal bulb and second part of the duodenum * Biopsies need to be performed while the individual is on a gluten-containing diet * Histological diagnosis based on the classification of Marsh, Marsh modified or Corazza classification * Increased HLA Class II and cytokine expression precedes abnormal histology * Intraepithelial lymphocytes * Crypt hyperplasia * Villous atrophy * Patchy involvement so multiple biopsies required

Answer 10

* Requires a specific genetic background (HLA DQ2 or HLA DQ8) * Patients have circulating IgA autoantibodies to tissue transglutaminase (tTG) a ubiquitous enzyme that catalyses deamination from a glutamine to lysine residue - increases afffinity for HLA * Serum IgA levels and tissue transglutaminase IgA antibodies or * tissue transglutaminase IgA antibodies and deaminated gliadin peptide IgG (DGP - IgG) * IgA endomyseal antibodies (performed in limited laboratories) * Where tTG-IgA and/or DGP IgG positive refer for confirmatory small intestinal biopsy

Answer 11

Testing Serology * Firstly confirm that the patient is consuming a normal, gluten-containing diet * Serum IgA levels and tissue transglutaminase IgA antibodies or * tissue transglutaminase IgA antibodies and deaminated gliadin peptide IgG (DGP - IgG) * IgA endomyseal antibodies (performed in limited laboratories) * Where tTG-IgA and/or DGP IgG positive refer for confirmatory small intestinal biopsy Genotyping * HLA DQ2 and HLA DQ8 found in 99% of patients with coeliac disease * 40-50% of the Australian community so most people with these genes will not develop coeliac disease * Main use of HLA DQ2/DQ8 genotyping to exclude a diagnosis of coeliac disease

Answer 12

**Clinical Classification** - RUQ: - Cholecystitis - Liver pathology - RLL pneumonia - RLQ: - Appendicitis - Ovarian pathology - Pyelonephritis - Right sided diverticulitis - Epigastric: - Peptic ulcer disease - Pancreatitis (usually radiates to back) - Inferior myocardial infarct - LLQ: - Diverticulitis - Ovarian pathology - Pyelonephritis - LUQ rare

Answer 13

inflammtory, secretory, osmotic; malabsorption/digestion; motility related fucntinal disease Investigations: - history: systemic disease; iatrogenic eg drugs radiation surgery; onset; pattern; duration; epidemiology; stool characteristic; abdominal pain and weight loss; aggrevating, mitigating -- fasting improves osmotic

Answer 14

Mechanisms of Liver Fibrosis - Generally restricted to conditions causing chronic liver damage. - Options for liver after Irreversible liver cell damage and loss: 1. Regeneration (mitotic replication of adjacent hepatocytes) – unfortunately with time replicative senescence occurs. 2. Scarring and fibrosis. --- #### Liver Scarring and Fibrosis - Involves a complex process of stellate cell activation/proliferation ➔ stellate cells become myofibroblastic ➔ collagen synthesis. --- ### Cirrhosis - The end-stage of many types of chronic liver disease/injury. - Not all end-stage liver diseases are cirrhotic. - Potential for reversal of fibrosis in future? - Reflects significant liver damage with scarring/fibrosis and functional/vascular derangements. - Consequences: - Liver dysfunction/failure. - Portal hypertension (bleeding). - Risk of hepatocellular carcinoma. Fatty Liver Disease - Identical histologic findings in both alcoholic and non-alcoholic forms (Clinical History !!!). - **Histologic Findings**: 1. Evidence of excess fat in hepatocytes (steatosis): - Macrovesicular (one large droplet) > microvesicular (multiple small droplets). 2. Evidence of damage to hepatocytes (steatohepatitis): - Ballooning degeneration. - Mallory-Denk bodies (degenerate intermediate filaments complexed with ubiquitin)., can be surrounded on neurtophils - Neutrophilic infiltrates. 3. +/- Fibrosis (begins “pericellular”).--progresses VIRAL HEPATITIS Viral Hepatitis - Infiltration by lymphocytes with any combination of: - Portal tract inflammation. - Interface hepatitis. - Lobular hepatitis (death of hepatocytes). - Variable degrees of fibrosis. - Viral serology is essential. **Chronic viral hepatitis** - dominated by lymphocytes - occurs in lobules, around portal tract, at interface **Hepatitis B** - ground glass hepatocytes: cytoplasmic inclusions - accumulation fo surface antigen - HepBsAg - can be seen on HE and on IHC **Hepatitis C** - often prominent lymphoid follicles - bile duct damage may be present - often steatosis ## Footnote note CLD can also be wilson, haemochrom, alpha 1 antitryspin

Answer 15

- **nonspecfic: anorexia weight los swkness fatigue** - decompensation: jaundice, pruritus, upper GIT bleed, abdminal distention, confusion - physical exam: jaundice, spider naevi, gynaecomastia, ascites, **heaptosplenomagely and hypersplenism,** palmar eryhtema, clubbing, **asterixis**, **bleeding and bruidsing easilt, decreased BP**, caput medusae, portal hypertension

Answer 16

**Liver Failure with Portal Hypertension** - Ascites - Dilated abdominal wall veins - Muscle wasting (check shoulders, buttocks, thighs) - Fullness left flank (splenomegaly) **Ascites Pathophysiology** - Cirrhosis - Low albumin - Low colloid oncotic pressure - - High portal pressure - Increased capillary hydrostatic pressure - High aldosterone and ADH - Na+, water retention Inevitably leading to - Fluid transudation - ascites **Sodium restriction** is an important consideration in the management of ascites, and educating patients about appropriate dietary modifications is essential. Salt substitutes are not recommended, and drugs that cause sodium retention (eg non-steroidal anti-inflammatory drugs [NSAIDs]) or contain relatively large amounts of sodium (eg antacids, effervescent preparations and some antibiotics) should be avoided. Treatment: **Diuretics** (see block 2 for specific information about each) and in refractory cases large-volume paracentesis (drainage); reduction of portal pressure by percutaneous insertion of a shunt between the hepatic and portal veins (transjugular intrahepatic portosystemic shunt [TIPS]).

Answer 17

**Complications of Cirrhosis** - Portal hypertension - Portal hypertensive gastropathy (vascular ectasia - oozy lining of stomach, vessels markedly dilated) - Oesophago-gastric varices (catastrophic upper gastrointestinal bleeding) - Thrombocytopenia (TPO down) - Ascites/ hepatic encephalopathy - Bacterial infection – impaired immunity (reduced complement synthesis), especially spontaneous bacterial peritonitis, septicaemia, pneumonia --- **Complications of Cirrhosis** - a complex conundrum **Metabolic Defects** - Hypoglycemia - Gluconeogenesis, glucose intolerance, diabetes - Impaired drug clearance (CYP-mediated metabolism, hepatic blood flow) **Circulatory Disorders** - renal failure - hepatorenal syndrome (renin-angiotensin-aldosterone, ADH activation) - hepatopulmonary syndrome (NO--> hypoxia, clubbing, pulmonary hypertension) --- **Hepatocellular Carcinoma (HCC) Complicates Cirrhosis** --- **HCC** - 2nd most common cause of cancer death worldwide - Incidence trebled in Australia and USA last 3 decades - Regard as a complication of cirrhosis (>90% of cases) - Most common in chronic viral hepatitis (B, C, B+C) - … and longstanding cirrhosis, especially males, HBV/HCV, alcohol, fatty liver (NASH) - Cholangiocarcinoma – less common; different associations e.g., primary sclerosing cholangitis, schistosomiasis

Answer 18

before= asymptomatic, mainly fatidue, third, dull or sharp aching abdo pian, thirst, sleep disrtbances, blaoting cirr or end stage: nausea vomit, jaundice, pruritus, hepatomegaly, acites, memory imp, blled, oss of appetiet clinical = can progress to steatohepatitis and cirrhosis

Answer 19

You cannot

Answer 20

Spectrum - Healthy liver - Fatty liver (Steatosis) >5% vol - at this stage, <1d/d women, <2 in men - Steatohepat*itis* (N/MASH) - Cirrhosis - irreversible step - HCC either from MASH, or cirrhosis - Alcohol-like liver histology in persons who don’t drink significant amounts of alcohol. Fatty Liver - Spectrum - Lobular inflammation - Ballooning degeneration - Perivenular fibrosis N/MAFLD - Why Bother? - 30% - Advanced liver disease in a subgroup [age >45, obesity, diabetes].- screen - Co-factor for other liver diseases. - Increased **cardiovascular risk**^[significant contributor to mortality], diabetes mellitus. - HCC risk. mAFLD - Pathogenesis - Main underlying mechanism: insulin resistance. - mAFLD is the hepatic manifestation of the metabolic syndrome. - Other important processes: lipotoxicity, oxidative stress, adipocytokines, mitochondrial defects, genetic factors. Clinical Presentation - Asymptomatic - Abnormal ultrasound, liver tests - ALT > AST - Enlarged, soft liver - Advanced liver disease not common - Look for metabolic syndrome: hypertension, type 2 diabetes, central obesity mAFLD - Natural History - Overall, 5% of mAFLD develop cirrhosis, 1.7% die of cirrhosis complications (mean follow-up 7 years). - Simple steatosis: benign outcome. - mASH: One-third will progress (fibrosis). - Cirrhosis 5%-10% over 5 years. - Poor outcome of mASH-related cirrhosis.

Answer 21

Principles of Treatment - lifestyle modification- aerobic and resistance exercise, eg Med diet; engaging personal trainer/dietitian/family support - targeting MetS components - liver-directed pharmacotherapy- only one recent drug, not mainstay - managing complications of cirrhosis - **Impact of Weight Loss on Improving Fatty Liver** - steatosis 35-100 - w/ weight loss >=103 - ballooning/inflammation 41-100 - w/ weight loss >=5 - NASH resolution in 64-90% - w/ weight loss >=7 - fibrosis in 45% - w/ weight loss >=10 Other treatments for MAFLD - bariatric sg when done for other metabolic disease - semaglutide no effect on fibrosis, steatosis; only in context of diabetes - other drugs not licensed except resmeritrom (thyroid hormone b-receptor), pioglitazone, vitamin E -- Principles of Treatment - No alcohol. - Nutritional supplements: thiamine, B12, folate - Corticosteroids (in severe alcoholic hepatitis).- only s-term, first 4 weeks therapy. Long-term does not improve outcomes - Managing cirrhosis complications (AFP, liver ultrasound, endoscopy- looking for varices). - Liver transplant (abstinence > 6 months, good social support demonstrated). Alcohol and Liver Disease - Safe limits important but liver risk variable. - Clinical spectrum: asymptomatic, big liver, “hepatitis”, cirrhosis/liver failure. - Suspicion important: MCV, AST > ALT. - Fatty liver reversible, hepatitis can progress, cirrhosis can progress. - Treatment: stop drinking, supplements, steroids, rarely liver transplant.

Answer 22

Heartburn: - substernal discomfort - radiation of pain toward mouth - precipitation by meals and recumbency - amelioration with antacid use **Symptoms** - oesophageal - heartburn - retrosternal burning pain, can radiate into neck, typically after meals or laying down - regurgitation - retrograde movement of acidic gastric contents into the mouth or pharynx - chest pain - extraoesophageal - cough - asthma - laryngitis - hoarse voice - dental erosions - globus sensation - feeling of something stuck in throat around sternal notch **Oeso vs extra symptoms** - extra- symptoms not as responsive to therapeutics - heartburn 50-70% will experience symptom relief from PPI - chest pain if positive pH study up to 80% - chronic cough, asthma, hoarse voice and pH negative chest pain , less than 25% will improve, some may get worse

Answer 23

**Pathophysiology** - Lower (o)esophageal sphincter – LOS/LES tone - Anatomical disruption on LOS - Oesophageal mucosal defences - Motility **Sphincter** - 3-4 cm, tonically contracted, smooth muscle - crural diaphragm provides an extra layer of protection - LOS and crural diaphragm together constitute the barrier - most of the time LOS is closed and opens in response to food in the oesophagus - transient LOS relaxations account for 50-70% of reflux events **TLOSR** - where teh LOS relaxes and intragastric pressure exceeds that of LOS, allowing for reflux of gastric contents into oesophagus - many factors decrease LOS tone - gastric distention e.g. large meal size - chocolate - caffeine - smoking - pregnancy - meds: nitrates, CCBs **Anatomical disruptions** - hiatus hernia is most common - pulls above diaphragm - LOS is shorter and weaker due to loss of support of crural diaphragm, leading to increased TLOSR - makes reflux more likely - can increase severity of erosive disease due to nocturnal reflux - volume reflux -- **Oesophageal mucosal defences** - pre-epithelial: - thin water layer with limited buffering capacity due to salivary bicarbonate - secretions from oesophageal submucosal glands - epithelial defences - cell membranes and the intercellular junctional complex limit the rate of hydrogen ion penetration into the intracellular space or cell cytosol - cellular and intracellular buffers (HCO3, proteins, phos) that neutralise back-diffusing luminal acid - cell membrane ion transports remove acid from the cytosol when intracellular pH falls to acidic levels **Breaching mucosal defences** - high luminal acidity, alcohol , heat causing caustic injury, smoke derived chemicals - acid attacks and damages intracellular junctions - increased paracellular permeability ie non-erosive reflux - acidification of intracellular space by back diffusion of luminal acid - cell oedema and necrosis - poor epithelial repair due to reduced salivary epidermal GFs - erosive reflux disease **Oesophageal and gastric motility** - reduced acid clearance by impaired oesophageal peristalsis - ineffective oesophageal motility present in about 50% of cases of acid reflux referred for manometry and pH studies - direction of causality unknown - swallowing of saliva which contains bicarbonate is essential to clear oesophageal acid and restoring oesophageal pH - primary oesophageal peristalsis is initiated by swallowing ~60/h - secondary peristalsis is not initiated by swallowing and can be triggered by luminal content and acid - re-reflux can occur when refluxate is cleared but trapped in a hernia sack increases oesophageal acid exposure time

Answer 24

**Red flags** - dysphagia - especially progressive from solids to liquids - weight loss - haematemesis or melaena - sudden change in reflux symptoms

Answer 25

Complications **Barrett's oesophagus** - the normal stratified squamous epithelium in the lower oesophagus is replaced wiht metaplastic columnar epithelium with both gastric and intestinal features - develops as a consequence of chronic GORD - other RFs include obesity, family Hx, smoking - increased risk of oesophageal adenocarcinoma: <1% /y - prevalence: 1.3-1.6/1000 endoscopies **Oesophageal cancer** - 60% Ad, 40% SCC in Au - SCC predominates in developing nations - Poor prognosis, 1700/y, 23% 5ys **Surgery for GORD** - especially if refractory disease - fundoplication: stomach wrapped around lower oesophagus - reinforces LOS - different types: 180, 270, 360 - surgery may also be done to fix hernia

Answer 26

** * Barrett’s oesophagus / adenocarcinoma - metaplasia (Squamous to glandular epithelium), *goblet cells* - biggest RF is untreated chronic reflux - can become dysplastic i.e. malignant potential, cytological features of malignancy, +/- BM invasion - if resected -- big section, implications for morbidity ** * Follows dysplasia-carcinoma sequence – therefore suitable for surveillance – anticipated decline in population treated with PPI’s Barrett’s esophagus - stratified squamous epithelium is replaced by metaplastic columnar epithelium which in turn predisposes to the development of adenocarcinoma of the oesophagus. Endoscopically it appears as salmon pink tongues of mucosa extending above the gastro-oesophageal junction (GOJ) and into the tubular oesophagus, replacing the stratified squamous epithelium that normally lines the distal oesophagus. Barrett’s oesophagus – squamous mucosa is replaced by glands with intestinal metaplasia, (numerous goblet cells) **Dysplasia in Barrett's** intracytoplasmic mucin droplets of varying sizes , nuclei are pleomorphic, darker, larger and disorganised with multiple layers indicating dysplastic change.

Answer 27

- oesophageal physiologic evaluation i.e. - endoscopy (structural overview of oesophageal and stomach - see LA grades) - ambulatory pH monitoring - adjunctive approach **Ambulatory monitoring** - wireless - Bravo capsule - attached endoscopically 3-5 cm above GOJ - wireless pH recording for up to 48h - capsule detaches spontaneously - attachment can cause chest pain and discomfort in some people - advantages: wireless, 48h - disadvantages: requires endoscopic insertion, possibility of chest pain post attachment, early capsule detachment, acid exposure time only (nothing else measured - look to see if pH dips below 4) - wired - 24 h pH - catheter based system - inserted while patient is awake therefore no anaesthetic risk - multiple catheter options - impedance capacity - advantages: multiple catheter option (Single or dual pH sensor +/- impedance i.e. flow across oesophagus- helps to assess response to treatment, disringuish GERD from NERD), inserted in clinic setting i.e. no endoscopy, simple reinsertion if catheter dislodged, no pain - disadvantages: unable to pass catheter nasally e.g. due to previous ENT surgery or anatomical abnormalities, if unable to tolerate catheter insertion, attached to box for 24h -can't have shower

Answer 28

**Anti-secretory medication** - H2 receptor blockers e.g. ranitidine, famotidine, nizatidine - PPIs e.g. omeprazole, esomperazole - P-CAB e.g. vonoprazan **MoAs** - H2Rbs - competitive antagonists that bind to histamine receptor in parietal cell, blocking the binding of histamine - gastrin stimulates release of histamine from enterochromaffin-like cell sin response to food which then bind to H2 receptor on partieal cells stimulatinf acid secretion - onet of action 1 h - laasts 4-6 hours - PPIs - irreversibly bind to and inhibit HK ATPase transporter on teh luminal membrnae of parietal cells - accumulate in the secretory canaliculus of the parietal cell where the active drug forms a disulphide bond with the external surface of the HK ATPase transporter - onset 30-60 m - takes 3-5 days to reach steady state - PCAB - competitive, reversible blockade of K binding site of the HK ATPase transporter on the luminal membrane of parietal cells - onset of action 30m - lasts 21 h - PPI> H2RB - unless under specific circumstances e.g. younger, or younger with functional - vonoprazan not funded by PBS - recommendation: 8-12 wks of once daily standard dose - only advised in patients with typical reflux symptoms e.g. heartburn, regurgitation and/or chest pain - note: dose between PPIs means different potency - lifestyle and acid modification - reduce foods and drinks that trigger TLOSR - coffee, alcohol and spicy foods - stop smoking: cigarette smoking increases TLOSR - weight loss - central obesity increases intra-abdominal pressure and reduces gastric compliance - sleep with head of bed elevated

Answer 29

paracetamol, drugs, no4

Answer 30

- Intrinsic or idiosyncratic drug-induced hepatotoxicity. - **Intrinsic**: Hepatotoxicity is predictable if dose is high enough. - **Idiosyncratic**: Hepatotoxicity results at therapeutic dose of drug. Often fatal if drug use continued - but not always: isoniazid induced liver injury can disappear even with continued use. Dose can still play a role by increasing the likelihood of injury

Answer 31

- Disrupted Ca2+ homeostasis -> blebbing -> cell death. - Disruption of actin filaments next to canaliculus, inhibition of transporters eg of bile. - Covalent binding of drug to cytP-450 - adducts. - Adducts migrate to plasma membrane - immune response. - Apoptosis - loss of nuclear chromatin. - Inhibition of mitochondrial function (loss of ATP and increase in ROS and build-up of fatty acids). Note also: bile duct epithelium can be damaged by toxic metabolites

Answer 32

Paracetamol Metabolism Mainly synthesised by phase II conjugation. Will switch to PHS/P450 systems. which generates NAPQI. Usually converted to not harmful metabolite with incorporation of glutathione. Pathways become saturated and deplete glutathione stores. If glutathione levels drop below 30% normal, NAPQI levels rise and cause damage. Prostaglandin H synthase is a minor pathway. NAC "replaces" glutathione. Is an analog of cysteine. (Golan et al. Principles of Pharmacology - 2nd edition). Mechanism of Toxicity At least 17 hepatic enzymes are known to be inhibited by NAPQI, likely more. - Microsomes (1) - Cytosol (10) - Mitochondria (4) - Cell membrane (2) 14 others bind directly to paracetamol but are not yet shown to be inhibited. Cell death likely due to multiple parallel events rather than a single mechanism. 3 major Mechanism of Toxicity - Uncouples mitochondria - GDH inhibited, inability to produce ATP - Depletes glutathione further, inhibits glutamylcysteine synhtetase - Disrupts Ca2+ homeostasis (Park et al. Annu Rev Pharmacol. Toxicol (2005) 45:177-202). Overall resultsin susceptibility to additional damage. - Altering gene expression, production of TFs, altered gene expression, protein activity and expression, in addition to... - Toxic metabolites, GSH depletion, and oxidative stress probably render hepatocytes more susceptible to the innate immune system (Kaplowitz Nature Reviews - Drug Discovery (2005) 4:489-499). - genetic susceptibility (either increased or decreased) identified in animal model KO studies #### Risk Factors for Paracetamol-induced Hepatotoxicity - Chronic alcoholism (more than 50g/day) - alcohol is usually metabolised by CYP450 - induces increased expression of CYP450 nad migration to membrnae - ethanol out-competes paracetamol hence NAPQI initially low - as ethanol is metabolised, and there is more P450, hence more NAPQI - Prolonged fasting - Other medications (inducers of cytP450 2E1 and 3A4) e.g., isoniazid, rifampicin, carbamazepine. Stimulated cytP450 enzymes & reduced glutathione levels in the liver increase the risk. - Enzyme inducers can enhance hepatotoxicity, not just ethanol: smoking, phenytoin, phenobarbital.

Answer 33

Risk Factors for Paracetamol-induced Hepatotoxicity - Chronic alcoholism (more than 50g/day) - alcohol is usually metabolised by CYP450 - induces increased expression of CYP450 nad migration to membrnae - ethanol out-competes paracetamol hence NAPQI initially low - as ethanol is metabolised, and there is more P450, hence more NAPQI - Prolonged fasting - Other medications (inducers of cytP450 2E1 and 3A4) e.g., isoniazid, rifampicin, carbamazepine. Stimulated cytP450 enzymes & reduced glutathione levels in the liver increase the risk. - Enzyme inducers can enhance hepatotoxicity, not just ethanol: smoking, phenytoin, phenobarbital.

Answer 34

New Drugs and Hepatotoxicity Hepatotoxicity is the reason why many new drugs never reach the market and is a major reason why drugs are withdrawn from the market. Examples include Bromfenac (NSAID) and Troglitazone (used in type 2 diabetes).

Answer 35

Herbal Remedies Some herbal remedies can cause severe hepatotoxicity, including Kava-Kava, Chaparral, Germander, Valerian root, Skullcap, Mistletoe, Senna, and Comfrey.

Answer 36

ALT and AST is moderately elevated AST is more often elevated than ALT ALP- less than 2-3 times elevated May be higher if cirrhosis is related to primary sclerosing cholangitis or primary biliary cirrhosis. GGT is non specific but correlated to cirrhosis when alcohol associated. Bilirubin may be normal in compensated and rise as disease progresses. Albumin level falls are synthetic liver function declines. Albumin can be used to help grade disease PT: this is the first clotting time to increase because of the short half life of FVII. Worsening coagulopathy correlates with severeity of hepatic dysfunction Important to remember this does not always mean more bleeding as the liver also synthesizes bodies natural anticoagulants (protein S, C) Hyponatremia: decrease ability to excrete free water Thrombocytopenia: due to decrease production of thrombopoietin and platelet sequestration in the spleen (main culprit). Anemia: mulifactoral, could be related to blood loss, folate deficiency, bone marrow suppression of anemia of chronic disease.

Answer 37

C, D, M, U Changes in motility, vsiceral hypersense, gastro perm alteration > 6 mo since onset: recurrent abdo pain > 1d/week un past 3 months, abdo pain relates to def, change in stooll freq or appearance --> 2 of 3

Answer 38

Multifactorial: psychoscial, environmental, physiological

Answer 39

Fits criteria, to the exclusion of others eg UC Non pharm: diet, triggers, low FODMAP, lifestyle: activity, stress, psychobehaviiural therapy Lopearmide, movical, antispasmodics for abdo pain

Answer 40

see tree - induce remission - maintain remission - 5ASA mainstay of UC to oinduce and maintain - use oral CCS if severe or not responsive - escalate to immods like AZA if severe - or monoAb vedo, infliximab - if acute and severe may try IV CCS For Crohns - mild mod oral CCS - severe Iv then oral CCS - maintenance: AZA/6MP, MTX-> inflix ada ustekin,m vedo Antibs: metronidazole or cipro if perianal fistula or abscess foramtion

Answer 41

A maladaptive pattern of substance use leading to clinically significant impairment or distress, as manifested by 2 or more of the following occurring within 12 mo - The severity of the disorder will be graded by the number of criteria the person meets. If it's 0 to 1, no diagnosis is made. From 2 to 3 criteria, the diagnosis is mild; 4 to 5, moderate; and 6 or more, severe.

Answer 42

Epi/RUQ pain fever nausea and vomiting SIRS

Answer 43

Pancreas is usually protected from autodigestion by mucus. In autodigestion protease breaks down muscle, lipase breaks down cell wall and amylase leads to membrane integrity loss.

Answer 44

alcohol, ERCP, gallstones ## Footnote associateions with obesity diabetes and smoking

Answer 45

endo vs exo insufficiency

Answer 46

interstitial>>>necrosis

Answer 47

- assess for fluid loss organ failure SIRS - fluid replacemnt in 24-48h - prophylactic if extrapanc - pain control - fluid management woudl help, potential opioids - close monoting and nutoronal support - progress to drain/debridement

Answer 48

- Anorexia - Confusion - enceph - Dark urine - bilirubin - Scratch marks - Liver tenderness - Black stools - depends, eg yes if varices - Peripheral stigmata: high sensitivity, spider naevi from SVC: nipple line to head

Answer 49

**Cholestasis** - Impaired bile flow - Jaundice common - Dark urine: bilirubinuria - Pale stools - Malabsorption - long chain fatty acids, fat-soluble vitamins (impaired coagulation) - Pruritus --- **Cholestasis does NOT (always) mean biliary obstruction!** There are many causes, the most common of which is due to mechanical obstruction of CBD - gallstones: pain, fever, jaundice (triad) - malignancy: pancreatic head, bile duct, other - scarring: primary or secondary sclerosing cholangitis - infection eg cholangitis, parasites **Some molecular (“medical”) causes** - Drug-induced cholestasis (eg amoxycillin/clavulanic acid) - Cholestasis of pregnancy - Primary biliary cholangitis (PBC, formerly known as PB cirrhosis)

Answer 50

alcohol metabolic syndrome lifestyle changes

Answer 51

Iron Homeostasis - Essential for life, involved in heme proteins, drug and steroid metabolism, and immune system - Total body iron: men 5 g, premenopausal women 3.5 g - Iron absorption occurs mainly from red meat; daily requirements small Daily requirements small – replace losses * Recommended daily intake (RDI): – Males and post-menopausal females 8 mg/day: absorb 10-15% (~1 mg/day) – Pre-menopausal females 16 mg/d, pregnant females 24 mg/d * Richest dietary source is red meat: vegetarians are at risk of iron deficiency ### Key Proteins of Iron Metabolism | Gene | Protein | Function | | ---------- | ----------- | ------------------------------ | | **Ferritin | Ferritin | Iron storage protein | | **Tf | Transferrin | Circulating iron carrier | | **TFR | Tf receptor | Receptor for Tf | | HJV | Hemojuvelin | Acts on neogenin | | SLC40A1 | Ferroportin | Iron transmembrane transporter | | **HAMP | Hepcidin | Iron regulatory hormone | Hepcidin: Iron Regulatory Hormone - Blocks ferroportin, the cellular iron exporter - Predominant negative regulator of iron absorption from the intestine and iron transport out of macrophages - Synthesis stimulated by iron and inflammation

Answer 52

Hereditary Hemochromatosis (HFE) - Single gene disorder, near HLA loci on chromosome 6p - Autosomal recessive disorder - Mutations in the HFE gene (C282Y, H63D) change HFE structure and function - other variants outdated, irrelevant - associated with iron overload: homozygous C282Y - 90% of genetic haemochromatosis in Au, compound C/H mild phenotype usually only shows up after taking excessive iron medication - homozygous H63D has no phenotype - HFE allele frequency is 8% in caucasian --> pseudo-dominant inheritance ie one parent homozygous recessive x heterozygous - Penetrance of HFE mutations is low (~30%)

Answer 53

Hereditary Hemochromatosis (HFE) - Single gene disorder, near HLA loci on chromosome 6p - Autosomal recessive disorder - Mutations in the HFE gene (C282Y, H63D) change HFE structure and function - other variants outdated, irrelevant - associated with iron overload: homozygous C282Y - 90% of genetic haemochromatosis in Au, compound C/H mild phenotype usually only shows up after taking excessive iron medication - homozygous H63D has no phenotype - HFE allele frequency is 8% in caucasian --> pseudo-dominant inheritance ie one parent homozygous recessive x heterozygous - Penetrance of HFE mutations is low (~30%) Penetrance of Hemochromatosis - Penetrance refers to the proportion of individuals with a disease-causing mutation who exhibit clinical effects.- thus phenotype:genotype 1:1 - Clinical penetrance of genetic hemochromatosis (GH), particularly C282Y homozygosity, is low. - Approximately 28% of males and 1.2% of females with C282Y homozygosity had iron overload-related disease. - Factors influencing penetrance include environmental (blood donation; physiological blood loss due to pregnancy or menstruation; diet vegetarian) and genetic factors, with recent studies suggesting genetic factors are more significant.

Answer 54

- Serum iron concentrations fluctuate; not a useful test - Transferrin saturation is a better indicator - Normal: 20 - 44% - Hemochromatosis: >50%, can be >90% - Iron deficiency <20%

Answer 55

Diagnosis of Hemochromatosis - Diagnosis is based on evidence of increased body iron stores, typically indicated by raised serum ferritin and transferrin saturation. - HFE gene testing is essential for family screening. - Liver stiffness measurement and liver ultrasonography are performed for diagnosis and surveillance. - Other tests not necessary eg MR quantitation of liver iron, or not done eg quantitative phlebotomy, and liver biopsy

Answer 56

Interactive Liver Toxicity - Excessive alcohol consumption most important factor contributing to cirrhosis - Excessive alcohol consumption synergistically interacts with iron overload, contributing to cirrhosis. - recommend NHMRC safe drinking ([[Gastroenterology - Lecture 6]]) - Obesity and type 2 diabetes further exacerbate liver disease, diabetes risk in patients with hemochromatosis. - Alcohol + obesity/T2D is double jeopardy - Alcohol + obesity/T2D + iron overload is triple jeopardy - Control of comorbidities ie alcohol and obesity is essential to prevent liver complications AND NOT JUST IN HAEMOCHROMATOSIS.

Answer 57

- Discuss with patients the importance of alcohol and weight moderation (diabetes, cirrhosis, liver cancer) - Venesection is recommended for patients with hemochromatosis (eg genetically proven) and evidence of iron overload (raised serum ferritin and transferrin). - Referral to specialized services is needed for difficult cases.

Answer 58

Common causes of intra-abdominal sepsis - Appendicitis - Cholecystitis - Pancreatitis - Diverticulitis - Perforated ulcer - Ischaemic bowel atomical Classification: Oesophagus-Stomach-Duodenum - Perforated peptic ulcer (mild until perforated = severe) - Gastric - Duodenal - Boerhaave’s syndrome - Spontaneous oesophageal rupture - severe and high mortality, rare - Iatrogenic injury - Gastroscopy - ERCP - PEG tube - Trauma Anatomical Classification: Liver / Gallbladder / Pancreas - Liver abscess - uncommon, pyogenic or non - Biliary colic – cholecystitis - Cholangitis (jaundice, fever, RUQ) - Gallstone ileus - Bile duct injury or bile leak after cholecystectomy - Acute pancreatitis - usu due to gall stones or alcohol Anatomical Classification: Small bowel - Meckel’s diverticulitis - Small bowel obstruction- usu due to adhesions - Acute mesenteric ischaemia- uncommon - Inflammatory bowel disease eg Crohn's - Hernia involving small bowel Anatomical Classification: Colon, rectum and appendix - Appendicitis - Diverticulitis - Right side - Sigmoid - Inflammatory bowel disease - Infectious or ischaemic colitis - Volvulus - Sigmoid - Caecal Anatomical Classification: Other - Kidneys, ureter, bladder - Renal colic - Pyelonephritis - Renal abscess - Cystitis - Female reproductive organs - Pelvic inflammatory disease

Answer 59

Cholecystitis **Clinical presentation:** - History of biliary colic, worse with food - Persistent RUQ pain - Nausea, vomiting, loss of appetite, fever - Murphy’s positive - push RUQ take a breath -- sharp pain **Diagnosis:** - Ultrasound (thickened wall, increased vascularity, pericholecystic fluid, tenderness to probe) - Assess LFTs to determine likelihood of choledocholithiasis - Ensure Lipase is not elevated - differential for pancreatitis Cholecystitis **Management of sepsis:** - Antibiotics - triple - Surgery - depends septic or no

Answer 60

Appendicitis **Clinical presentation:** - Migratory abdominal pain (periumbilical -->RLQ) - Loss of appetite, nausea/vomiting - common young - Fever - RLQ peritonitis - Rovsing’s (push on left - pain on right), obturator positive/psoas (lift right leg elicits pain) **Diagnosis:** - Clinical diagnosis (Especially in young, men) - Suspicious raised by elevated inflammatory markers - If doubt about diagnosis, imaging: - US vs CT Management of sepsis: - **Triple antibiotics** (metronidazole, ampicillin, gentamicin) - **Surgery** - timing depends on patient stability

Answer 61

haemic bowel **End of the line result for a number of pathologies** - Mesenteric ischaemia - eg atrial fibrillation and embolism, chronic ischaemia with thrombosis/stricture - Strangulated hernia - venous congestion, arterial insufficiency - Closed loop adhesional small bowel obstruction **Clinical presentation:** - Non-specific abdominal pain (may or may not localise, various regions) - Pain out of proportion to examination - Can be difficult to diagnose, needs high degree of suspicion **Diagnosis:** - CT (may see thickened wall, free fluid) - Lactate sometimes elevated (not always) Ischaemic bowel **Management of sepsis:** - Antibiotics - Surgery

Answer 62

Pancreatitis **Clinical presentation:** - Epigastric pain radiating to back - Nausea, vomiting, loss of appetite - Fever **Diagnosis:** - 2/3 of: - Clinically typical symptoms - Elevated lipase >3x upper limit normal - CT findings consistent with pancreatitis - Identify cause: - Biliary ultrasound - gstones - Screen for secondary causes (Lipids, Igg4 subclasses, Ca 19.9, MRCP) - classification mild moderate severe depending on local complications, organ failure and timeline of failure Pancreatitis **Management of SIRS:** - No antibiotics - Supportive care - Prevent further episodes - Cholecystectomy prior to discharge if gallstones are the cause - Treat complications of pancreatitis - Avoid surgery (mostly)

Answer 63

Diverticulitis **Clinical presentation:** - LLQ pain - Fever - Diarrhoea or constipation - LLQ or suprapubic peritonitis **Diagnosis:** - Elevated inflammatory markers - CT diagnosis - CT also used to assess severity Diverticulitis **Management of sepsis:** - Antibiotics - Control of sepsis - Abscess -> drainage - Purulent or faeculant peritonitis -> surgery

Answer 64

rforated ulcer **Clinical presentation:** - Sudden onset upper abdominal pain - Fever, nausea - History of NSAIDs without PPI, smoking, untreated helicobacter pylori - Peritonitis in upper abdomen **Diagnosis:** - CT showing free gas and free fluid in upper abdomen; lipase normal Perforated ulcer **Management of sepsis:** - Antibiotics (triple) - Surgery

Answer 65

**Acute hepatitis (hepatocellular necrosis)** - Anorexia (profound), nausea, vomiting - Lethargy - Jaundice common - Scleral icterus especially in people of colour --- **Acute hepatitis (hepatocellular necrosis)** - also: - Dark urine: bilirubin-uria - Tender (soft) liver - Acute liver failure - not making clotting factors hence bruising/bleeding, prolonged coagulation time (not corrected by vitamin K injection) - Liver biochemistry: ALT >10 fold increased; changes in BR, GGT, ALP less specific

Answer 66

**What are Parasites?** - **Protozoa** – single-celled eukaryotes - **Metazoa** – multi-celled eukaryotes - **Helminths** - worms - **Arthropods** – insects; cause disease or serve as vectors (Murray et al. 2002)

Answer 67

**Parasite Hosts** - Host specificity - range of different hosts in which a parasite can mature - can be fairly specific to a particular host species - **Definitive Host**: parasites mature into adult form; Adult undergoes sexual reproduction; - **Incidental Host**: Parasite develops but does not mature sexually; may undergo asexual reproduction - also paratenic: parasite alive and infective but no development - incidental: intermediate; does not allow transmission to another host - Humans may serve as - Definitive - Intermediate - Incidental/Dead end e.g. humans as definitive host for tapeworm: - eat cyst or larval form in pork - adult tapeworm develops in intestine - eggs excreted in faeces e.g. humans as intermediate host for tapeworm: - eat egg in contaminated food or water - larvae released and migrates to various tissues and encysts - will only complete lifecycle *if another human eats tissue with cysts*

Answer 68

**Giardia** - *G. lamblia* = - *G. intestinalis* = - *G. duodenalis* - Giardia has a wide host range in which it can complete its entire lifecycle - Common - Transmission from contaminated water or directly such as in childcare centres **Pathophysiology of Giardia infection** - Excystation occurs in response to exposure to stomach acid, releasing four trophozoites (TZ) - TZ colonise the small intestine - TZ undergo rapid asexual reproduction - Encystation occurs as TZ transit through the large intestine **Pathophysiology of Giardia infection – Encystation** - Flattening of the villi and inflammation of the mucosa is observed - Pathophysiological mechanisms potentially including - Direct damage to the intestinal brush border and mucosa - Alteration of absorption - Alteration of small intestinal function - Induction of a host immune response resulting in secretion of fluid and damage to the gut **Symptoms** - range from - asymptomatic - chronic diarrhoea - epigastric pain - nausea and vomiting - bloating and flatulence - malabsorption - weight loss - symptoms: 6-15 days after exposure - usually last several days but are self limiting **Treatment of Giardiasis** - Treatment - Metronidazole - Tinidazole

Answer 69

**Cryptosporidium** - thick walled oocyst ingested, sporulated thick walled oocyst excreted, contaminates water and food - Note – resistant to chlorination. Outbreaks can be associated with water supply, swimming pools **Pathophysiology of Cryptosporidium infection** - goes through several lifecycle stages - asexual and sexual cycles **Cryptosporidium Infections - Symptoms** - Immunocompetent adults - self-limiting gastroenteritis lasting 1-2 weeks most commonly characterized by watery diarrhea - Immunocompromised populations – potentially disseminated disease and/or life threatening symptoms - Cholera-like illness - Chronic diarrheal illness - Intermittent diarrheal illness - Transient diarrheal illness Extremely difficult to treat - Nitazoxanide – need to import to Australia under special access scheme

Answer 70

- worldwide distribution - young children - asymptomatic - perianal itching - sleep disruption - migration into vagina - abdominal pain - appendicitis

Answer 71

Strongy hook scabies Tvaginalis

Answer 72

Salmonella: General Characteristics - **Motile, Gram-negative rods** - **Facultative anaerobes** - **Resistant to bile salts**, although poor resistance to acids ^[contrast with [[#Shigella General Characteristics]]] - **Non-lactose fermenting**, but do ferment xylose - XLD agar can be used to differentiate Salmonella from Shigella - **Grow within a wide temperature range (≤54°C)** - Grows optimally at 37°C - *Psychrotrophs (2-4°C) --- Salmonella: Taxonomy - **Taxonomy based on genomic relatedness** show that there are two Salmonella species: - *S. bongori* - *S. enterica* - *S. enterica* has a further 6 subspecies: - *S. enterica subspp. arizonae* - *S. enterica subspp. diarizonae* - *S. enterica subspp. enterica* - *S. enterica subspp. houtenae* - *S. enterica subspp. indica* - *S. enterica subspp. salamae* - There are **>2500 serovars/serotypes for *S. enterica***. - **Most of the pathogenic Salmonella serovars are found within *S. enterica subspp. enterica*** - *e.g.,* *S. enterica subspp. enterica serovar Typhimurium* generally shortened to *S. enterica serovar Typhimurium*, and Salmonella paratyphi ?. --- Salmonella: Classification - **Non-typhoidal**: Cause acute gastroenteritis - Most infections caused by *S. enterica serovar Typhimurium* and *S. enterica serovar Enteritidis*. - Large animal reservoir, transmitted to humans via food in *developing* and developed countries. - **Typhoidal**: Cause enteric (typhoid/paratyphoid) fever - Most infections caused by *S. enterica serovar Typhi* and *S. enterica serovar Paratyphi*. - *S. enterica serovar Typhi* associated with asymptomatic carriage (gall bladder usually the reservoir). - **Infect humans only, common in developing countries**/areas of poor sanitation, faecal-oral route of transmission. --- Salmonellosis: Gastroenteritis - **Most common form of salmonellosis** in developed countries, typically associated with low mortality. - **High infectious dose** (~10^5 cells) - **Incubation**: 2-7 days, **Duration**: 2-7 days - **Symptoms**: vomiting, fever (more with Typhi), abdominal cramps, watery diarrhoea with PMNs - Inflammatory diarrhoea: due to invasion - Osmotic diarrhoea: due to loss of absorptive surface - similar mix to shigellosis diarrhoea - **Usually self-limiting**, antibiotics not prescribed unless: - Extraintestinal disease develops (typically bloodstream infection) - Severe gastroenteritis * * * * - Infants and immunosuppressed individuals --- Typical Sources of Non-Typhoidal Salmonella - **Commensals in birds (and other animals)** - Poultry meat and eggs are common sources of infection --- Salmonellosis: Enteric Fever - In Australia, **most cases are acquired overseas** i.e. returned travellers - **Low infectious dose** (10–100 organisms) - **Incubation**: 7–28 days (*Typhi*), 1–15 days (*Paratyphi*) - **Symptoms**: Prolonged fever, vomiting, abdominal cramps, diarrhoea with PMNs, headache, myalgia, nausea, (+/-) rash of flat rose-coloured spots. - Inflammatory + Osmotic diarrhoea - **Humans are the only hosts** for these species - **Transmission**: Faecal-oral route and person-to-person spread by chronic carrier - After infection, people can **carry the organisms for months to years** --- ## Treatment Of Typhoidal Salmonellosis - **Antibiotics should be started as soon as enteric fever has been confirmed.** - Identify and treat carriers of *S. enterica* serovar Typhi and *S. enterica* serovar Paratyphi: - **Antibiotics** - Or cholecystectomy (if antibiotics fail); sometimes patients will elect to do this - Ideally, *Typhoid carriers should be excluded from jobs involving food handling and preparation.* --- Salmonella: Virulence Strategies - **Invasiveness**: - Intracellular survival and multiplication in intestinal epithelium and macrophages. - **Type III secretion system and effector proteins (SPI-1)** required for *initial invasion* into intestinal epithelium. - **Type III secretion system and effector proteins (SPI-2)** required for *replication* in intestinal epithelium and macrophages. - **LT-like toxin and other enterotoxins**. - **Capsule** (*S. enterica* serovar Typhi only). --- Typhoidal Salmonella: Systemic Infections (I) - **Organism is consumed**. - **Enter lamina propria via M cells**. - **Taken up by macrophages**. - **Migrate in macrophages to mesenteric lymph nodes and multiply**. - **Released into the bloodstream (1° bacteraemia, low level, typically asymptomatic)**. - **Removed from blood by macrophages in spleen, bone marrow, liver; multiply and re-enter bloodstream (2° bacteraemia, onset of symptoms i.e. headache, malaise, fever)**. - **Re-enter GIT via gall bladder**, replicates asymptomically but enters GIT and sheds, or causes bouts of typhoid fever

Answer 73

- **EIEC and Shigella** are genotypically nearly identical. - Have same virulence factors and strategies - Cause a syndrome identical to Shigellosis - **EIEC can be differentiated from Shigella** only by a very limited number of tests based on utilisation of different nutrients, including utilisation of serine, xylose and/or sodium acetate, and mucate fermentation - EIEC isolates may be positive for one or more of the tests **but Shigella are generally negative** - Do not fit the full definition for the “genus” Shigella

Answer 74

Shigella: General Characteristics - **Non-motile, Gram-negative rod** - **Facultative anaerobes** - **Resistant to gastric acid and bile salts** - **Non-lactose/xylose fermenting** - Inability to ferment xylose can be used to distinguish Shigella spp. from Salmonella spp. (black colonies) from clinical samples and from food using Xylose Lysine Desoxycholate (XLD) agar (red colonies) --- Shigella spp. - **Four species**: - *Shigella sonnei* (most infections: mild form of disease) - *Shigella flexnerii* (more severe form of the disease) - *Shigella boydii* (more severe form of the disease) - *Shigella dysenteriae* (most serious form of the disease) - **Human pathogens** exclusively – no animal reservoirs. - **No environmental reservoirs**. - **Faecal-oral spread**, contaminated foods, *flies act as mechanical vectors. --- Shigellosis - **Primarily a paediatric disease in developing countries**. - Acute onset: Incubation 1–4 days, Duration 2–3 days. - **Small infective dose** (10-100 organisms). - **Epidemics occur due to overcrowding and insufficient sanitation**. - Refugee camps, nurseries, day-care centres and other residential facilities - **Symptoms**: - Spectrum: Mild to severe depending on the species (As well as host factors) - (+/-) Fever, abdominal cramps, severe and bloody diarrhoea - especially with dysentery, often with pus (PMNs) and mucus ^[stool MCS shows leucocytes] - Inflammatory diarrhoea: due to invasion - Osmotic diarrhoea: due to loss of absorptive surface --- Shigella: Virulence Strategies - **Invasiveness**: - Intracellular survival, multiplication, and intercellular spread - Shigella can lyse the phagocytic vacuole (phagosome) and replicate in the cytoplasm - in this way it can escape host defences - **Type III secretion system and effector proteins** required for invasion and escape from the vacuole - **AB5 exotoxin (Shiga toxin)** and other toxins (e.g., SigA) - **IcsA autotransporter**: - Outer membrane protein - Localised at pole of bacterium - Facilitates host-actin polymerisation, brings pathogen closer to epithelial cell, thereby faciltiating intracellular spread【Sansoneh (2004)】

Answer 75

- **Motile, Gram-positive rod**. - **Widespread among animals and the environment**. - Found in plants, soil, and surface water samples in addition to being in sewage, food, and human/animal faeces. - **Outbreaks associated with high-risk foods**: - Unpasteurised milk, soft-serve ice-creams, and soft cheeses (brie, camembert, ricotta), raw vegetables, cold deli meats, raw seafood. - **Infectious dose (<1000 organisms)**. - **Grow optimally at 37°C, but *Psychrotroph**: 2–4°C.* - Infections most common in immunocompromised individuals, pregnant women, neonates, and the elderly <65. --- Listeriosis - **Symptoms**: - In healthy adults it is usually asymptomatic. - Flu-like illness and/or Gastroenteritis: nausea, vomiting, fever, diarrhoea + PMNs. - Inflammatory and osmotic diarrhoea. - In 5 - 10% of the population, *L. monocytogenes* is present in the intestinal tract. - In at-risk populations: bloodstream infection, sepsis, chorioamnionitis, meningo-encephalitis - One of the few bacterium that can cross both the placental and blood-brain barrier. - **Treatment**: IV benzylpenicillin ^[higher doses may be required i.e. for CNS infections] --- L. monocytogenes: Virulence Strategies - **Adhesion**: - Listeria adhesion protein (LAP) - Fibronectin binding protein A (FbpA) - **Invasion**: - Invasion A (InlA) - Invasion B (InlB) - **Vacuolar Rupture**: - Listeriolysin O (LLO) - Phospholipase A (PlcA) - Phospholipase B (PlcB) - **Intracellular Spread**: - Actin-assembly-inducing protein (ActA)【Radoshevich & Cossart (2018)】

Answer 76

- **Motile, Gram-negative “comma-shaped” rods**. - **Microaerophilic (5-7% O2)**. - **Most species grow well at 42°C (thermophilic)**. - **Taxonomically classified in the same order as Helicobacter** ^[when first characterised H pylori was called 'Campylobacter sthng']. - *Campylobacter jejuni* and *Campylobacter coli* are the species most commonly implicated in human GIT infections. --- Campylobacteriosis - **Gastroenteritis**, can lead to Guillain-Barré syndrome. - **Low-Medium infective dose (~500 organisms)** - **Incubation period of 2 – 11 days**. - **Duration**: 3 days – 3 weeks, relapses take place in 15 – 25% cases. - **Symptoms** include abdominal cramps and fever, *vomiting rare*, bloody diarrhoea + PMNs (inflammatory and osmotic diarrhoea). - Rare complication- GBS (see also [[Immunology B4 - Lecture 3]]) - **Organism is excreted for several weeks unless treated with antibiotics (erythromycin), but typically self-limiting**. --- Sources Of Campylobacter - **Common GIT commensal of chickens and other animals** (cattle, pigs, dogs, wild birds, etc.). - **Common cause of foodborne illness in developed countries** (particularly contaminated chicken and unpasteurised milk). - **While invasive, mechanism not well understood**. - Infrequently causes invasive/extraintestinal disease esp. if host is immunocompromised - **Inflammatory process consistent with invasion of intestinal epithelium, M-cell uptake, and with the production of bloody diarrhoea + PMNs**. --- Campylobacter: Virulence Strategies - **Invasiveness**: - Intracellular survival and multiplication. - **Surface structures**: - **Capsule important for virulence, epithelial cell adherence, and invasion.** - Lipooligosaccharide (LOS) required for epithelial cell adherence and invasion. - LOS structures of *C. jejuni* can display molecular mimicry of neuronal gangliosides (linked to Guillain–Barré syndrome). - Flagellum required for colonization, virulence and epithelial cell invasion, and also acts as a secretion apparatus for invasion antigens. - **Cytolethal distending toxin**: - Causes DNA damage promoting inflammation and cell death.

Answer 77

**(Osmotic) Diarrhoea** - Caused by an excess amount of poorly absorbed nutrients (i.e., malabsorption) that remain in the intestinal lumen - Examples include lactulose and magnesium - Causes retention of water in the lumen through osmotic effects - **Attaching/Effacing (A/E) lesions:** - Result from destruction of intestinal microvilli and induction of cytoskeletal rearrangements directly beneath intimately attached EHEC organisms - Mediated by Intimin and Tir - Decreases surface area for nutrient absorption, causing the intestinal contents to increase in osmolarity, leading to secondary osmotic diarrhoea **Secretory diarrhoea** - Through increased secretion or decreased absorption of fluids and electrolytes - e.g. Vibrio cholerae, ETEC - disease is mediated by exotoxins in the gut **Inflammatory diarrhoea** - Through inflammation causing damage to host tissues resulting in fluid exudation - e.g. C. difficile - mediated by direct damage to the IEC barrier and disruption of tight junctions

Answer 78

- **Bacterial Exotoxin:** Soluble proteins secreted into extracellular environment by some species of Gram-positive and Gram-negative bacteria. - Toxins can attack different cell types: - Enterotoxins - Neurotoxins - Leukotoxins - Cytotoxins - Can act through specific mechanisms: - **Botulinum toxin (Clostridium botulinum):** blocks neurotransmitter release leading to paralysis (botulism) - **Streptolysin O (Streptococcus pyogenes):** haemolysis - **Pertussis toxin (Bordetella pertussis):** alters cell function leading to cell death ## Footnote - **Bacterial Endotoxin:** LPS (lipopolysaccharide) present in Gram-negative bacteria. An intrinsic feature of the bacterium

Answer 79

**Intoxication** - Results when a host ingests pre-formed exotoxin - Ingested enterotoxins directly cause disease - Presence of a replicating pathogen is not required for disease - often requires shorter incubation time eg hours, as pre-made toxin is cause of symptoms **Infection** - Results when a pathogen colonises a part of the body and subsequently causes disease - Often pathogens will then synthesise toxin which causes toxin-mediated disease - often slightly longer incubation time eg 1-2 days compared with intoxication (hours)

Answer 80

**Vibrio cholerae** - Gram-negative, facultative anaerobe, highly motile bacillus with a single polar flagellum (locomotion organelle). - Persists in natural aquatic reservoirs and infects human host via consumption of contaminated water/food. - People with access to adequately treated water typically not exposed. - Areas without adequate water treatment still suffer from epidemic infection. - Causative agent of cholera, an acute diarrhoeal disease which can be fatal without treatment. - A type of secretory diarrhoea - Estimated 3–5 million cases and 100,000–120,000 deaths due to cholera every year. --- **Cholera: Clinical Features and Treatment** **Clinical features** - Acute profuse watery diarrhoea with severe dehydration (can lead to hypovolaemic shock and death if untreated) **Treatment** - Cholera is a readily treatable disease - Up to 80% of infected people can be treated successfully with prompt administration of oral rehydration solution - Severely dehydrated patients require administration of intravenous fluids - May also require adjunctive antibiotics to attenuate duration of diarrhoea, reduce volume of rehydration fluids needed, and shorten duration of V. cholerae excretion --- **V. cholerae Colonisation Factors** - Colonisation is dependent on production of a type IV pilus, toxin coregulated pilus (TCP), which is essential for adhesion to the small intestine. - N-acetylglucosamine-binding protein A (GbpA) is also required (mediates binding to intestinal mucin). - Colonisation of the gut is a pre-requisite for the subsequent production of toxins which are directly responsible for the profuse diarrhoea. - V. cholerae causes toxin-mediated disease --- **V. cholerae Toxins** - V. cholerae has 7 different toxins that together result in a particularly severe diarrhoea. - **Cholera toxin (CT), accessory cholera toxin (ACE), NAG-stable toxin, and V. cholerae cytolysin (VCC):** affect ion secretion into the intestinal lumen. - **Haemagglutinin/protease (HA/P), repeats in toxin (RXT), and zonula occludens toxin (Zot):** promote the loss of barrier function. --- **Cholera Toxin Structure** - Consists of an A subunit bound to a pentameric ring of B subunits, where the B subunits are responsible for delivery of the A subunit into the host cell. --- **Cholera Toxin Function** - **CT (A subunit):** causes Cl− secretion and Na+ absorption, leading to an increase in NaCl levels in the intestinal lumen. - **CT (A subunit):** activates adenylate cyclase: catalyses conversion of ATP to cAMP. - **cAMP:** increases activity of the chloride (CFTR) transporter. - **cAMP:** decreases activity of sodium (NHE2/NHE3) transporters. - Modulation of both receptors causes elevated concentrations of Na+ and Cl– ions in small intestinal lumen which becomes hyperosmotic compared to cells lining the intestines. - Causes osmosis of large volumes of water into the intestinal lumen from the cells and ultimately from the bloodstream. - Water exits the body in form of diarrhoea, resulting in dehydration. --- **Enterotoxigenic Escherichia coli (ETEC)** - Gram-negative, facultative anaerobe, motile bacillus. - Infects human host via consumption of contaminated food/water. - Causative agent of traveller’s (abundant watery) diarrhoea in developing countries. - Also secretory diarrhoea (along with V.cholerae ) - Responsible for an estimated 300,000 - 500,000 deaths annually in children aged <5 years. - Clinical features and treatment are similar to cholera (emphasis on rehydration and electrolyte replenishment). --- **ETEC Colonisation Factors** - Colonisation of the small intestine is essential for ETEC infection - A variety of different structures are required for adhesion: - **Fimbriae (e.g. CFA/I)** - **Pili (e.g. ECP)** - **Non-fimbrial adhesins (e.g. Tia, TibA)** - Colonisation of the gut is a pre-requisite for production of toxins that are directly responsible for causing the watery diarrhea - ETEC causes toxin-mediated disease --- **ETEC Toxin Structure and Function** **Heat labile toxin (LT)** - Similar to CT in structure (AB5) and function **Heat stable toxin (ST)** - Small cysteine-rich peptide - Binds to receptor (guanylyl cyclase C) on surface of small intestinal epithelium: catalyses conversion of GTP to cGMP: - **cGMP:** increases activity of chloride (CFTR) transporter - **cGMP:** decreases activity of sodium (NHE3) transporter - Causes Cl– secretion and Na+ absorption, leading to an increase in NaCl levels in the intestinal lumen --- **Enterohaemorrhagic Escherichia coli (EHEC)** - **Gram-negative**, facultative anaerobe, motile bacillus - **Infects human host via consumption of contaminated food/water** - Primary sources of EHEC outbreaks are raw or undercooked ground meat products, unpasteurised milk, and faecal contamination of vegetables or drinking water - **Causative agent of diarrhoea, haemorrhagic colitis (HC), and haemolytic uraemic syndrome (HUS) ^[anemia, thrombocytopenia, and **renal failure**] in developing and developed settings** - a type of osmotic diarrhoea - Common cause of renal failure in young children **Symptoms:** - Diarrhoea which can be bloody **Treatment:** - Rehydration and renal-supportive therapy - Antibiotics are not recommended due to increased risk of HUS --- **EHEC Colonisation Factors** - Colonisation of the large intestine is essential for EHEC infection - A variety of different structures are required for adhesion: - **Intimin and Tir** - **Long polar fimbriae (Lpf)** - **Haemorrhagic coli pilus (type IV pilus)** - **Non-fimbrial adhesins** (e.g., OmpA, Efa1, Iha) - EHEC colonisation of the gut is a pre-requisite for production of toxins which contribute to the diarrhoea --- **Attaching/Effacing Lesion-Mediated (Osmotic) Diarrhoea** - Caused by an excess amount of poorly absorbed nutrients (i.e., malabsorption) that remain in the intestinal lumen - Examples include lactulose and magnesium - Causes retention of water in the lumen through osmotic effects - **Attaching/Effacing (A/E) lesions:** - Result from destruction of intestinal microvilli and induction of cytoskeletal rearrangements directly beneath intimately attached EHEC organisms - Mediated by Intimin and Tir - Decreases surface area for nutrient absorption, causing the intestinal contents to increase in osmolarity, leading to secondary osmotic diarrhoea --- **Shiga Toxin-mediated Diarrhoea** - Shiga toxins (Stx) 1 and 2: - Antigenically distinct AB5 toxins responsible for the progression to HUS (bind to renal cells) - Stx A subunit inactivates host ribosomes, thereby inhibiting protein synthesis (translation) - Both Stx1 and Stx2 inhibit intestinal absorption of water, causing luminal fluid accumulation which exits the body as diarrhoea --- **Clostridioides difficile** - See notes from "Normal Gut Flora" Lecture - **Gram-positive bacillus**, obligate anaerobe, spore-forming - Part of the normal gut flora - Leading cause of healthcare-associated infectious diarrhoea, with spectrum of disease ranging from: - Uncomplicated diarrhoea, inflammatory type - Systemic toxic effects leading to significant colonic inflammation, sepsis, and death - A hospital “superbug” due to the difficulties in treatment and the propensity to spread in nosocomial settings - Economic burden of C. difficile infection estimated at $800 million annually in the US --- **C. difficile Infection** - Most important risk factor for C. difficile infection (CDI) is the recent administration of broad-spectrum antibiotics which cause gut dysbiosis - CDI can also occur when environmental spores are ingested and then reach the large intestine - Spores comprised of several heat/chemical-resistant layers, allowing them to survive acidic environment of the stomach - Bile salts within the small intestine trigger germination of spores into vegetative cells in the large intestine --- **C. difficile Transmission** - Stopping transmission of C. difficile to other individuals is important and challenging. - C. difficile can easily spread by direct or indirect exposure to a patient or the patient’s environment: - Exposure to contaminated care equipment or high-touch surfaces in patients’ room/bathroom - Transfer of bacterial spores to patients via hands of healthcare workers - Oral vancomycin and metronidazole are used as treatment, however these antibiotics do not kill spores. - Bleach should be used to clean contaminated surfaces as normal cleaning products may be ineffective against spores. - Hand-washing preferred over handrubs for hygiene --- **C. difficile Clinical Features and Treatment** **Clinical features:** - Diarrhoea (can range from mild self-limiting to severe haematochezia, abdominal cramps, and abdominal pain) - Pseudomembranous colitis (inflammation of the colon)- so named because C diff overgrowth forms layers resembling membranes - Toxic megacolon (acute toxic colitis with dilation of colon) which can result in perforation of the colon, sepsis, and death **Treatments:** - Antibiotics including vancomycin (oral), metronidazole (oral or IV), fidaxomicin (oral) - Faecal microbiota transplant (FMT) – disease remission in up to 92% of cases - Surgical removal of colon (for severe toxic megacolon) --- **C. difficile Colonisation Factors** - Colonisation (and overgrowth) within the large intestine is essential for C. difficile infection - A variety of different structures are required for adhesion: - **S-layer proteins** - **Cell wall proteins** (e.g., Cwp66) - **Fbp68 fibronectin-binding protein** - **FliC-FliD components of flagella** - Colonisation of the colon is a pre-requisite for production of toxins that are directly and indirectly responsible for causing the (inflammatory) diarrhoea - Inflammatory diarrhoea is characterised by bloody stools, small-volume mucous stools, and fever --- **C. difficile Toxins** **Toxin A (TcdA)** - 308 kDa, binds to receptor (glycoprotein gp96) on the apical surface of colonic epithelial cells - Causes direct alterations in barrier function **Toxin B (TcdB)** - 270 kDa, gains access to basolateral surface of colonic epithelial cells after tight junction disruption, binding to an unidentified receptor **Binary toxin (CDT)** - 147 kDa, actin-specific ADP ribosyltransferase that destabilises the cytoskeleton and potentiates toxicity of TcdA and TcdB, contributing to the severity of infection - TdcA/B can be detected by PCR in stool, part of diagnostic toolkit for C. diff --- **C. difficile TcdA and TcdB Toxins** - Potent cytotoxic enzymes that specifically glycosylate small GTPase protein Rho, leading to disruption of cytoskeletal integrity and cytotoxicity. - Trigger an extensive inflammatory cascade resulting in damage to host tissue and release of inflammatory exudative fluid into the colonic lumen (appears mucous-y due to presence of WCCs). - Activate enteric nerves and (Toxin A) promote the release of neuropeptides, which elicit Cl– secretion from intestinal epithelial cells (therefore diarrhoea also has a secretory component) --- **TcdA/TcdB-mediated inflammation (inflammasome activation)** - TcdA and B are potent cytotoxic enzymes that specfically glycosylate small GTPase RHo, leading to disruption fo cytoskeletal integrity and cytotoxocoty - triggers an extensive inflammatory cascade resulting in damage to host tissue and release inflammatory exudative fluid into the colonic lumen - activate enteric nerves and *toxin A* promotes release of neuropeptides, which elicit Cl- secretion from intestinal epithelial cells - hence diarrhoea has a secretory component but it is by and large inflammatory **Pathogenesis of C. difficile-associated Diarrhoea** - Toxin-induced inflammation damages tight junctions and the IEC barrier resulting in fluid exudation (inflammatory diarrhoea) - Part of the inflammatory response includes neutrophils which release an adenosine precursor that activates CFTR thereby promoting Cl– secretion (secretory diarrhoea) - Continual destruction of intestinal epithelium from inflammation results in: - Exudation of blood and serum into the lumen (bloody diarrhoea)- note may not be so bloody in mild disease - Destruction of absorptive epithelium (osmotic diarrhoea)

Answer 81

Rota paeds, noro epidemic

Answer 82

*General features* - Small, but very tough - Non-enveloped - Resistant to drying - Hard to disinfect - Rapid disease course - Incubation down to 24 hr - Symptoms from 24 hr to 7 days - Spectacular replication - Low minimal infectious dose, ≤ 10 infectious units - Massive yield, up to 1010 infectious doses excreted *Viruses that cause gastroenteritis* - Rotavirus - Pediatric diarrhoea - Norovirus - Epidemic gastro - Adenovirus - Serotypes 40 and 41 (less frequent) - Astrovirus - Not discussed

Answer 83

**Rotavirus vaccines** - Multiple infections with rotavirus are possible - BUT these are often with different serotype - AND are generally much less severe These suggest that a vaccine might work - Live attenuated vaccines best explored - Single genotype (attenuated human rotavirus) - Rotarix (GlaxoSmithKline) G1P1[8] - Mixtures of reassortant viruses - RotaShield (withdrawn after a single year in 1999, long story…) - RotaTeq (CSL/Merck) G1, 2, 3, 4 P1[8] - Rotarix and RotaTeq in the National Immunisation Program as of 2007 - Given at 2 and 4 (R’rix) or 2, 4 and 6 months (R’Teq) **Multivalent rotavirus vaccines (e.g. RotaTeq)** - Reassortants have different gene segments from different viruses; on attenuated bovine rotavirus backbone - rotateq has 4 G-types and one human P-type in its collecton **Rotavirus in Australia 2008 vs 2014** - Hospitalisations and Emergency department visits reduced by 71% for under 5s - 7000 admissions avoided Source: Immunise Australia website **Impact on mortality** - Data on mortality from Mexico - decreased significantly *Richardson V et al. N Engl J Med 2011;365:772-773.* **Does the vaccine drive serotype change?** - In Australia different states use different vaccines - Rotarix (G1, P8) states (inc NSW and ACT) - RotaTeq (G1,2,3,4, P8) states (inc Vic, Qld, SA) - short answer: yes, selecting for those with different serotype, but does not seem to confer resistance - no data suggesting reduced efficacy of vaccines - may be down to steady P serotype *Roczo-Farkas et al. Communicable Diseases Intelligence Volume 40 No 4 – December 2016*

Answer 84

**Rotavirus vaccine and intussusception** - There is a small increase in risk of intussusception, especially within a week of the first dose - data is suspect - TGA, 2011 - Minimise risk: - Stick to schedule (esp. upper age limit) - Don’t vaccinate risk groups (immunocompromised or ill) - Vigilance, advise parents (severe colic, fever, bloody stool, drawing legs up)

Answer 85

- Original strain was Norwalk Virus - An outbreak of gastro occurred at a Norwalk school - A rectal swab taken and a bacteria-free sample made - Fed to adult volunteers, their stool collected - Serially passaged to other volunteers - Virus identified by immune electron microscopy - Volunteers needed for serum and virus samples - Similar viruses were called Norwalk-like viruses - AKA small round structured viruses **Studying noroviruses is very hard** - Human norovirus cannot be grown in culture - Only host is human - Only source of norovirus is human poo - Only way to test virus viability is to feed it to humans **Volunteers have contributed greatly…** - A mouse norovirus is the only one that grows well in culture; one other calicivirus genus can be grown **Lots of extrapolation required…** - With enough virus, the genome can be sequenced - Individual proteins can be expressed and studied

Answer 86

**Molecular biology ** - Norovirus is a member of the calicivirus family - Calici from calyx, Latin for cup - Discovered in ’60s by EM - Characteristics - + sense, linear, ssRNA genome, ~7.5 kb -> straight to ribisome - + or positive = genome same sense as mRNA - Non-enveloped virion: bleach and water/soap - Replicates in the cytoplasm - Other caliciviruses - Saporovirus (GI disease in humans) - Rabbit calicivirus used as biological control agent **Noroviruses are relatively simple** - Capsid composed of one major and one minor protein - Major capsid protein (VP1) forms virus-like particles - The genome is a single strand of + sense RNA - has three open reading frames **ORF1 makes a polyprotein** - A common trick used by viruses - Cleaved into individual proteins by the viral proteinase - A total of 8 proteins including the 2 capsid proteins - Approximately 2500 amino acids in total - Many mammalian proteins are bigger!

Answer 87

**Rotavirus disease and pathogenesis** - Typical disease course - 3 days of vomiting that starts first - 5 days of diarrhoea that overlaps the vomiting - Most emphasis is on the cause of diarrhoea - Direct viral damage to enterocytes at the tips of villi - Shortening of villi, malabsorption and secretion before, after, during - BUT diarrhoea does not entirely correlate with damage - Work in animal models suggests it’s more complex - Incubation from ½ to 2 days - Disease course - Acute symptoms generally last ½ to 2½ days - Rapid disease almost diagnostic: - Kaplan’s criteria for identifying norovirus outbreaks

Answer 88

**Adenoviruses** - Adenoviruses (AdV) - Adeno from adenoid - Found in 50s using cell culture - Originally associated with human respiratory disease - Human AdV has 6 species (A-F) and 51 serotypes - Characteristics - Linear, dsDNA genome ~35 kb - Non-enveloped virion- survives stomach to cause disease there and elsewhere - Replicates in the nucleus - Other adenoviruses - Adenoviruses infect fish, reptiles, birds and mammals **Adenoviruses do lots of nasty things** TROPISM dependent - Disease - Upper respiratory infections - Pneumonia - Epidemic keratoconjunctavitis - Gastroenteritis - Menigoencephalitis - Hepatitis (kids with transplants) - Myocarditis - Acute haemorrhagic cystitis

Answer 89

- **Normal flora** - Synonymous with microbiota, indigenous microbial population, microflora, commensal flora. - A collection of microbial species found on tissue surfaces of normal healthy individuals. - Coexist with the host in a non-disease-inducing manner, and are beneficial to the host. - Includes those that can become opportunistic pathogens . - Normally harmless organisms that can cause infection/disease when host immune system is compromised or natural barrier defences are breached - Microbial communities that colonise the human gastrointestinal tract (GIT): - GIT is organ site of largest microbial biomass - Comprising 1012 -1013 bacteria in colon. - Of at least 500-1,000 bacterial species. - Composition of community varies within different parts of the GIT and between individuals. - Plays a pivotal role in health and disease. - BUT ALSO INCLUDES: - Fungi (mostly Candida yeast e.g. Candida albicans). - Protozoa (controversial but include Blastocystis and Entamoeba). - Eukaryotic viruses - Prokaryotic viruses (including bacteriophages/phages)

Answer 90

Microbial Dysbiosis - Altered or imbalanced normal gut flora can result in dysbiosis, which is associated with several human diseases. - This imbalance can mean 3 things: 1. Loss of beneficial microbial organisms in our gut. 2. Expansion of potentially harmful microorganisms. 3. Loss of microbial diversity. These are not mutually exclusive and can occur at the same time. Microbial Dysbiosis: Causes & Disease - Dysbiosis can be caused by various factors including deterioration of health, old age, malnutrition, diet, stress, genetics, infection, and antibiotic usage. - Antibiotic usage – kills large numbers of normal gut flora, offering an ecological niche to bacteria that would not otherwise be able to compete. - multiple consequences: asthma, coeliac, RA, obesity, NASH, NAFLD, stress Microbial dysbiosis and chronic intestinal disease - While specific causality is unclear, there is a link between microbial dysbiosis and: - Irritable bowel syndrome (IBS) Ø Increased Firmicutes:Bacteroidetes ratio, decreased Bifidobacterium - Inflammatory bowel disease Ø Increased bacterial numbers in mucosa, decreased bacterial diversity - Colorectal cancer Ø Increased Fusobacterium spp., E. coli - Obesity Ø Increased Firmicutes:Bacteroidetes ratio, decreased bacterial diversity **Gut virome in human disease** huge diversity, also play role in disease

Answer 91

- Normal gut flora can also cause disease by known means, such as antibiotic-induced dysbiosis leading to infection with opportunistic pathogens (C. difficile), or upon escaping their natural habitat into abdomen/bloodstream when intestinal mucosa is compromised (e.g. when intestinal integrity disrupted, Bacteroides fragilis). C. difficile infection - Gram-positive spore-forming, anaerobic bacillus considered a member of the normal gut flora (~5% of population). - Loss of normal gut flora barrier effect following broad spectrum antibiotics allows C. difficile to colonize and overgrow in the colon. - egs beta lactams (ceftriaxone, piperacillin-tazobactam), clindamycin, fluoroquinolones eg ciprofloxacin - spectrum of disease from diarrhoea and abdominal pain to pseudomembranous colitis, to toxic megacolon and death - Interaction of C. difficile with intestine leads to toxin release causing various symptoms. - Mild diarrhoea - Pseudomembranous colitis (inflammation of the colon) - Toxic megacolon (acute toxic colitis with colon dilation) - Death - C. difficile secretes toxins that are internalised by host cells through receptor-mediated endocytosis. - Toxins cause disruption to cytoskeletal architecture, which leads to cell death. - Toxin-mediated cell death results in the loss of intestinal barrier integrity and the translocation of bacteria into underlying/deeper tissues including bloodstream. - Toxin-mediated damage to the epithelium activates the host inflammatory immune response. - An overly robust inflammatory response can be damaging to the host and contribute to disease pathology. B. fragilis infection - Gram-negative, anaerobic bacillus and prevalent member of the normal gut flora. - Highly beneficial to the host (breaksdown complex carbohydrates, releases anri-inflammatory cytokines) - Probiotic to treat a range of disorders characterised by up-regulation of pro-inflammatory cytokines (e.g. IBS, multiple sclerosis, autism, etc.) - When intestinal integrity is disrupted, B. fragilis can escape into peritoneum, causing abscesses or peritonitis; or in blood causing bacteraemia and sepsis - Treatment includes antibiotics targeted against B fragilis, reconstitution of gut flora, surgical procedures to drain pus and remove necrotic tissue if necessary

Answer 92

- Age - Health (comorbidities eg cancer, stress, hormones, immunity) - Lifestyle & physical activity - Geographical location - Diet & nutrition - Genetics - Medication eg antibiotics, PPIs - Mode of birth - Infant feeding type

Answer 93

§ Prebiotics: Ø Nutritional compounds used to promote growth of beneficial gut flora. § Probiotics: Ø Bacterial cultures that restore the population of beneficial gut flora. § Faecal microbial transplantation (FMT): Ø Isolation of beneficial bacteria from the faecal matter of healthy donor to replace disrupted populations in diseased individuals. Ø FMT is successful in treating C. difficile infection, with disease remission in up to 92% of cases. Ø FMT has promising results in the treatment of post-infectious IBS and and various other gut microbiome imbalances (e.g. ulcerative colitis). § Antimicrobials (other than classical antibiotics): Ø Eliminate pathogens or manipulate the normal gut flora to benefit the host.

Answer 94

**CAUSES OF PEPTIC ULCER DISEASE:** - Helicobacter pylori - NSAIDs - The rest: - Cancer especially if of a certain age - Other drugs - Zollinger-Ellison syndrome (Gastrinoma) - In 1983, Warren and Marshall described an ‘unidentified curved bacillus on gastric epithelium in active chronic gastritis’ Lancet 1 (8336): 1273-75. - Successfully cultured under microaerophilic conditions, on chocolate agar, at 37°C - Gram-negative - Initially thought to be Campylobacter, now known as Helicobacter pylori (Hp) --- **KOCH’S POSTULATES** *Heinrich Hermann Robert Koch* Criteria used to establish a causative relationship between a microbe and a disease - The microorganism must be present in every case of the disease but absent from healthy individuals - The suspected microorganism must be isolated and grown in pure culture - The same disease must (should) result when the isolated microorganism is inoculated into a healthy host - The same microorganism must be isolated again from the diseased host --- **OUTCOME OF HUMAN EXPERIMENTS** - Marshall developed transient gastritis (MJA 142;436 1985) - Morris developed persistent gastritis which resolved after sequential therapy with doxycycline and bismuth subsalicylate (Am J Gastroenterol 82:192 1987)

Answer 95

**TREATMENT** - Triple therapy, most commonly used in Australia, involves: - Proton pump inhibitor (PPI) with - Two antibiotics: - Most commonly used – clarithromycin and amoxicillin - Also – metronidazole, tinidazole, tetracycline, azithromycin, levofloxacin - Quadruple therapy may also be used – includes bismuth compound **HIGH INCIDENCE OF ANTIBIOTIC RESISTANCE IN DEVELOPING COUNTRIES** **CHOICE OF ANTIBIOTICS** - Choose two antibiotics with different modes of action: - Amoxicillin - for peptidoglycan; - Tetracycline - Clarithromycin - Azithromycin - for the ribosomes

Answer 96

- cagA (cytotoxin-associated gene A), a 128-140 kDa protein that is co-expressed with; - VacA (vacuolating cytotoxin) that causes cell injury - 85-100% of patients with DU have cagA+ strains, compared to 30-60% of infected patients who do not develop ulcers - Host genetic factors (sensitivity to gastrin, higher parietal cell mass – cells that secrete HCl) - Environmental factors: smoking (73 vs 27%), NSAID use (61 times more likely if colonized by Hp), alcohol usage --- **HOW DO HP SURVIVE IN THE STOMACH?** - Hp use urea present in gastric juice - Urease enzyme produced by every strain to combat the acidic environment of the stomach by producing ammonia - Breaks down urea into NH3,which neutralises acid, and CO2 - Cytosolic urease can constitute up to 10% of bacterial protein - Basis of the urease breath test - 2-6 sheathed unipolar flagellae for motility through the mucus layer - Chemotaxis: sensors will be on the lookout for bicarbonate or neutral compounds - Lipopolysaccharide (LPS) and outer membrane proteins for adherence to host cells - vacA (exotoxin) and secretory enzymes (mucinase, lipase, protease) cause gastric mucosal injury (Acute and chronic inflammation) - Type IV secretion system for injecting effectors - cagA (effector) causes actin remodeling, IL-8 induction, inhibits apoptosis and T-cell activation and proliferation **HP TYPE IV SECRETION SYSTEM AND CAGA** - cagA encoded on a pathogenicity-associated island (PAI)- e.g. antibiotic resistance genes - More commonly associated with symptomatic disease and cancer - PAIs, in general: - Encode genes involved in virulence - Large segments of DNA encode numerous genes - Acquired through horizontal gene transfer - A pathogenic strain may have more than one PAI

Answer 97

**DIAGNOSTICS – HP TESTING** - Urease breath test – detection of C14 labelled urea - Endoscopy and biopsy – histology or CLO test - to check out complications or confirm healing - Blood test – antibody test - Stool antigen test **DISADVANTAGES** - Urease breath test: - False-negative results possible in the presence of PPIs and recent antibiotic or bismuth compound use. Less sensitive than biopsy test. Considerable resources and personnel required to carry out test. Not widely available. - CLO test (biopsy test): - Invasive ie needs endoscopy. Expensive. - Antibody test: - Cannot confirm whether it is a past or present infection. Not recommended for confirming eradication. - Stool test: - False-negative results possible in the presence of PPIs and recent antibiotic or bismuth compound use. Stool collection may be considered distasteful to the patient. **ADVANTAGES** - Urease breath test: - Provides rapid results (when available). Excellent specificity and very good sensitivity. - CLO test (biopsy): - Allows culture and therefore determination of antibiotic resistance profiles. - - Blood antibody test: - Inexpensive, widely available, very good NPV. - Stool test: - Identifies active Hp infection. Excellent PPV and NPV regardless of Hp prevalence. Useful before and after therapy. --- **CONFIRMATORY TESTS FOR HP ERADICATION:** - In patients treated for Hp, eradication of infection should be confirmed four or more weeks after the completion of therapy. - PPIs should be withheld for one to two weeks prior to repeat testing to reduce false-negative results. - Serologic testing should not be performed to confirm eradication as patients will continue to have antibodies after eradication.

Answer 98

**Gastrointestinal tract Histology** * Mucosa * Submucosa * Muscularis propria * Adventitia/Serosa **Mucosa ◼ epithelium ◼ lamina propria ◼ muscularis mucosae **Submucosa** loose collagenous tissue containing blood vessels, lymphatics, nerve submucosal plexuses (meissner’s) and lymphoid aggregates **Muscularis Propria** generally two layers of smooth muscle (inner circular and outer longitudinal) to allow for peristalsis, and nerve plexuses (myenteric) **Adventitia** loose supporting tissue containing blood vessels and nerves **Serosa** Mesothelial lining covering the outer most aspect of gastrointestinal tract **Adventitia vs serosa** Adventitia – found all parts of GIT, lies between muscularis propria and serosa (in some parts of bowel minimal to non- existent) Serosa – outer most lining of those parts of GIT found within abdomen (similar to pleura of lungs)

Answer 99

**Functions of GIT mucosa** * Protection - barrier to external environment * Secretion - and synthesis of various substances (e.g digestive enzymes, mucus, antibodies, hormones) * Absorption - products of digestion, water, electrolytes * Immunological functions - containing lymphoid tissue **Oesophagus** * Lumen is lined by protective stratified squamous epithelium * Primary function is to transfer ingested food and fluids from mouth to stomach * Thin lamina propria contains lymphoid tissue --> immune role **Stomach mucosa** **Stomach mucosa – cell types** * Fundus and body consist of straight tubular glands (formed by simple columnar epithelium) - note surface cells are low columnar or cuboidal * Contains large mucinogen granules which maintain the thick mucus sheet protecting epithelium * Surface mucous cells secrete bicarbonate, helps to protect epithelium from acidic gastric juices * Parietal cells: secrete gastric acid and intrinsic factor (needed to absorb vitamin B12 in terminal ileum), stain pink (many mitochondria) * Chief cells: secrete pepsin, stain blue (many ribosomes) http://www.lab.anhb.uwa.edu.au/mb140/default.htm **Gastric glands – cell types** * Neuroendocrine cells – secrete hormones such as serotonin and gastrin * Stem cells – can differentiate into any of other cells as required ---> constant turnover of cells Found in antrum villous mucosa lined by columnar mucosa with goblet cells of duodenum * Simple columnar epithelium * Enterocytes: absorptive cells with microvilli, cover villi and crypts * Goblet cells: scattered along epithelium and produce mucus http://www.siumed.edu/~dking2/erg/GI125b.htm **Small intestine epithelium** * Paneth cells: base of crypts, contain secretory granules of lysozymes, can phagocytose some bacteria and protozoa * Neuroendocrine cells: produce hormones such as secretin (important for digestion- regulates pH) * Stem cells: at base of crypts -- regeneration and high cell turnover - Intraepithelial lymphocytes: mainly T cells \ \ Mucosa with crypts lined by columnar mucosa with goblet cells of large intestine **Large Intestine mucosa** * Simple columnar epithelium which forms tubular glands (crypts) * Enterocyte, - absorptive cell - microvilli (most common cell type) * Goblet cells produce mucus, needed to lubricate intestine and allow for passage of bowel contents * Stem cells found at base of crypts http://www.kumc.edu/instruction/medicine/anatomy/histoweb/gitract/gitract.htm stratified squamous epithelium of anus

Answer 100

**Stomach mucosa – cell types** * Fundus and body consist of straight tubular glands (formed by simple columnar epithelium) - note surface cells are low columnar or cuboidal * Contains large mucinogen granules which maintain the thick mucus sheet protecting epithelium * Surface mucous cells secrete bicarbonate, helps to protect epithelium from acidic gastric juices **Gastric glands – cell types** * Parietal cells: secrete gastric acid and intrinsic factor (needed to absorb vitamin B12 in terminal ileum), stain pink (many mitochondria) * Chief cells: secrete pepsin, stain blue (many ribosomes) http://www.lab.anhb.uwa.edu.au/mb140/default.htm **Gastric glands – cell types** * Neuroendocrine cells – secrete hormones such as serotonin and gastrin * Stem cells – can differentiate into any of other cells as required ---> constant turnover of cells

Answer 101

**Oesophageal-gastric junction (usually called gastro-oesophageal junction)** stratified squamous epithelium of oesophagus columnar epithelium of stomach **Gastro-duodenal junction** Cell types are the same but the structure of the epithelium changes. Simple columnar epithelium of stomach vs villous mucosa lined by columnar mucosa with goblet cells of duodenum **Ileo-caecal junction** lined by columnar mucosa with goblet cells and Paneth cells of ileum vs Mucosa with crypts lined by columnar mucosa with goblet cells of large intestine **Recto-anal junction** glandular mucosa of rectum vs stratified squamous epithelium of anus

Answer 102

2nd most common across sexes. Age-specific rates, generally low until 50. Steadily rises after 50 with slight male predominance, then drops over time. Incidence and mortality are falling over time. 5YS: Improved to 70%. **Colon Cancer: Lifetime Risk** - male 1/10 if lives to 85 - female 1/15 --- **Colon Cancer Risk from Age 50-84** - 1/10 in males, 1/15 in females - hence >50 y cut off for screening --- **Risk Factors for Colon Cancer** - Age (as shown in age specific rate graphs) - Family history - Personal history of CRC or “at-risk” polyps - Inflammatory bowel disease -- **Genetic Causes of CRC** - ~1-5% of CRC is associated with germline mutations - - ~75% of CRC is sporadic - no family history is apparent **Epidemiological Risk Factors for CRC** - Diabetes mellitus - Alcohol - Obesity - Acromegaly **Controversial Associations** - Smoking - Coronary artery disease - Ingestion of red meat - Role of the microbiome **Risk Factors for Early-Onset CRC** - males - Caucasian - family history - obesity and hyperlipidaemia-- may explain high rates - NOT smoking - but alcohol does **Protective Factors: Drugs** - Aspirin - Other NSAIDs (e.g., sulindac) - Statins (controversial) - Hormone replacement therapy (HRT) - Antioxidants (controversial) - Green tea **Protective Factors: Uncertain** - Physical activity - Diet – fruit and vegetables - Fibre intake - Resistant starch - Folic acid - Vitamin B6 (pyridoxine) - Calcium - Vitamin D - Magnesium - Garlic - Fish consumption **Clinical Features** - Abdominal pain (site of neoplasm dictates location of pain and pattern e.g. periumbilical and colicky if near ileo-caecal valve, bilateral lower abdomen if in left side of colon) - Obstruction - Perforation - Localized spread (especially rectal cancers) - Peritoneal spread - Change in bowel habit esp if sigmoid/rectum, unlikely if right-sided - Bleeding (= ulceration) - Visible/identifiable blood per rectum (overt) - Occult (covert) bleeding leading to iron deficiency anaemia - Anaemia (Fe deficient, fairly common presentation) - Weakness - Weight loss **Right-Sided vs Left-Sided Cancers** _Right-Sided_ - Liquid stool - Iron deficiency anaemia without other symptoms (falling Hb and MCV even if still in normal range) _Left-Sided_ - Formed stool - Abdominal pain - Change in bowel habit - Rectal bleeding **Metastatic Disease** - Anorexia, vomiting, early satiety - Fatigue - Weight loss - Abnormal liver tests - Abdominal distension (ascites or hepatomegaly) - Spread most commonly to draining lymph nodes and liver but also to lungs, bone, brain, skin (nodules) --- **Symptoms and Prognosis** - Asymptomatic cancers (picked up by screening) generally have a better prognosis - Acute surgical presentations (bowel obstruction or perforation), likely to have peritoneal seeding, and have a poor prognosis - Presence of metastatic disease (20% of cases) indicates a poor prognosis **Diagnosis** - Symptoms (see above) - Asymptomatic (population screening) - Examination - Abdominal mass - liver, RIF mass - Lymphadenopathy - Hepatomegaly or ascites - Rectal mass eg on DRE - rare - Supportive blood tests - Iron deficiency anaemia (in appropriate age group) - Abnormal liver tests (possible metastatic disease) - Diagnostic tests - Colonoscopy - definitive test - Barium enema - CT colonography

Answer 103

* Commonest mesenchymal tumour of GI tract * Extraintestinal examples eg. mesentery * Recapitulate Interstitial Cells of Cajal (ICC) – “pacemaker” cells of gut, neural and myoid features -- can have neural and myoid appearance * Cause célèbre of targeted therapy * Most (85%) GISTS in kids lack C-KIT or PDGFR muts , and more commonly have succinate dehydrogenase muts (adults will almost always have these) * Sporadic vs. Inherited – NF1 (SI), Carney Triad (Paraganglioma, GIST, pulmonary chondroma), Carney Stratakis syndrome (Paraganglioma, GIST, SDH muts), Familial GIST Syndrome (KIT muts) Molecular genetics GIST * Majority of GIST (80-85%) have KIT mutations – Usually gain-of-function; exon 11, also 9, 13, 17 – Results in abnormal activation of gene, “switches on” cell proliferation and survival pathways * Most others are wild type (10-12%) or have PDGFRα mutations (5-7%) – PDGFR mutations are associated with myxoid and epithelioid phenotype and gastric location – Exons 12, 18 * Kit and PDGFR mutations apparently mutually exclusive - BUT those with PDGFR mutations often still express CD117 protein GIST demographics * Sporadic – commonest in 40-60 group; slight male preponderance * Syndromic/special types: – Carney’s triad (GIST, pulmonary chondroma, paraganglioma) – Familial GIST * rare, autosomal dominant; germline kit or PDGFR mutation * multiple tumours, ICC hyperplasia – Paediatric GIST * Median age 12, 75% female, 70% epithelioid – NF1-associated * Usually spindled, CD117 negative * Usually intestinal, often multiple * Often Imatinib-resistant – Other associations: tuberous sclerosis, others GIST histology - macroscopy: dumbbell shape * Spindled, elongated cells and nuclei * Epithelioid * Other variants (signet ring, oncocytic, rhabdoid, small cell, ...) * Majority express CD117, CD34, DOG-1 -- pathognomic * May express neural and/or myoid markers Behaviour * Histology is an imperfect predictor of behaviour: size, mitotic rate, necrosis * Varies with site: – Oesophageal: rare, most are malignant – Gastric: commonest, fundic more often malignant than antral – Small bowel: less often malignant – Colorectal: less common but 50% malignant, often aggressive * Mets to liver/peritoneum; other sites rare * Molecular genetics relevant

Answer 104

Gastric carcinoma demographics * Second most common tumour worldwide * Predominantly disease of developing countries + Japan; less common in Aus * Highly lethal – tends to present late (except in Japan!) – limited treatment options GC RFs ENVIRONMENT: * (atrophic gatsritis with intestinal metaplasia) – Helicobacter pylori infection – Autoimmune gastritis * Diet: nitrosamines, salty foods, low consumption of fresh fruit and vegetables/fibre * Tobacco, smoking * Radiation * Gastroenterostomy, ?bariatric surgery * Obesity * Low SES * Viruses, e.g. EBV? GENETICS: – Susceptibility to H pylori – Familial gastric cancer: e-cadherin (CDH1) mutation (herieditary Diffuse Gastric Cancer) – HNPCC/Lynch. Peutz-Jeghers, BRCA, AD Fundic Gland Polyposis, Cowden’s Syndrome GC: histology * Adenocarcinoma: “intestinal” or “diffuse” – Many shared genetic aberrations eg p53 – Diffuse type: e-cadherin mutation – Intestinal type: genes implicated in colorectal cancer eg. APC, TGFB * Gastritis -> intestinal metaplasia -> dysplasia -> intramucosal carcinoma -> invasive cancer The intestinal-type of Gastric Carcinoma is related to many of the risk factors previously alluded to: often occurs on the background of chronic gastritis → atrophy → intestinal metaplasia → dysplasia → adenocarcinoma The diffuse-type of gastric carcinoma is NOT related to many of the risk factors previously alluded to except hereditary diffuse gastric carcinoma **Diffuse type:** Diffusely infiltrating small groups and single cells (often signet-ring cells). E- Cadherin loss or mutation means that cells cannot adhere/stick to each other → diffuse pattern, no glands - ## Treatment and behaviour * Surgery is mainstay for curative intent * Chemo - Herceptin for cases with HER2 overexpression * Pattern of metastases: – Intestinal type (distal stomach, men) -> liver – Diffuse type (premenopausal women) -> ovaries (“Krukenberg tumour”) – Both -> peritoneal spread * 5-year survival Stage I = 95%; Stage IV = 7%

Answer 105

Adenocarcinoma of oesophagus * Typically arise at gastro-oesphageal junction, may be difficult to distinguish from proximal gastric cancer * But usually arises in Barrett’s mucosa * Follows dysplasia-carcinoma sequence – therefore suitable for surveillance – anticipated decline in population treated with PPI’s Barrett’s esophagus - stratified squamous epithelium is replaced by metaplastic columnar epithelium which in turn predisposes to the development of adenocarcinoma of the oesophagus. Endoscopically it appears as salmon pink tongues of mucosa extending above the gastro-oesophageal junction (GOJ) and into the tubular oesophagus, replacing the stratified squamous epithelium that normally lines the distal oesophagus. Barrett’s oesophagus – squamous mucosa is replaced by glands with intestinal metaplasia, (numerous goblet cells) **Dysplasia in Barrett's** intracytoplasmic mucin droplets of varying sizes , nuclei are pleomorphic, darker, larger and disorganised with multiple layers indicating dysplastic change. **Diagnosis**: endoscopy and histology appearance Well differentiated invasive adenocarcinoma Architectural changes – invasive glandular pattern, very poorly formed and disorderly glands with a cribriform pattern. In a background of desmoplastic stroma. + Cytological features of malignancy Poorly differentiated Marked nuclear and cytoplasmic pleomorphism, very no recognizable glandular structures. Adenocarcinoma is diagnosable in this instance due to the **presence of intracytoplasmic mucin vacuoles which have a clear appearance, often appearing as signet rings with a squashed, indented nucleus pushed to one side **Adenocarcinomas in summary** * MAKE GLANDULAR STRUCTURES WITH LUMINA * +/OR PRODUCE MUCIN * INTRACYTOPLASMIC * EXTRACELLULAR

Answer 106

* Simple columnar epithelium * Enterocytes: absorptive cells with microvilli, cover villi and crypts * Goblet cells: scattered along epithelium and produce mucus http://www.siumed.edu/~dking2/erg/GI125b.htm **Small intestine epithelium** * Paneth cells: base of crypts, contain secretory granules of lysozymes, can phagocytose some bacteria and protozoa * Neuroendocrine cells: produce hormones such as secretin (important for digestion- regulates pH) * Stem cells: at base of crypts -- regeneration and high cell turnover - Intraepithelial lymphocytes: mainly T cells **Small intestine submucosa** Submucosa of duodenum can be distinguished by presence of submucosal mucus producing glands, Brunner’s glands lymphoid tissue H+E: duodenum x50 www.technion.ac.i l/~mdcourse/2742 03/lect10.html H+E: duodenum x100

Answer 107

PPI **MoA** - irreeversibly inactivate theHK ATPase system or proton pump, on parietal cells - termainal step in acid secretory pathway (suppression is more complete than H2 receptor antagonists) - suppressing both stimulated and basal acid secretion (regardless of stimulus - histamine, gastrin, Ach) - when PPIs are stopped, acid secretion is restored by synthesis of new HK ATPase PPIs are pro-drugs converted to active metabolites by acids in the canaliculus of the gastric parietal cell **Adverse effects:** - generally well tolerated - serious toxicity rare but includes; anaphylaxis, hepatitis and interstitial nephritis - Possible increased risk (associated with prolonged therapy): - _C. difficile_-associated colitis - community-acquired pneumonia - hip fracture (high doses > 1 y) - decrease vitamin/mineral absorption such as B12 and Mg

Answer 108

- **5- Aminosalicylates (5-ASA)** - Steroid (prednisone, prednisolone, budesonide) - immunosuppression (azathioprine/methotrexate) - cyclosporin - Anti-TNF (infliximab) or other biological agents including vedolizumab Crohn's disease: - steroid (prednisone, prednisolone, budesonide) _together with_ - immunosuppression (azathioprine/6-mercaptopurine /methotrexate) - Anti-TNF (infliximab) or other biological agents including vedolizumab and ustekinumab - _5-ASA has a limited role_ 5-ASA **MoA** **5-ASA is an agonist for peroxisome proliferator activated receptor gene-γ (PPARγ) -> stimulation of PPARγ decreases inflammation in the bowel mucosa.** **Indications** **The mainstay of maintaining remission in UC** (can also be used to induce remission in mild disease). The active agent, 5-ASA, is delivered to the site of action in various formulations: - Sulfasalazine (5-ASA conjugated to sulfapyridine) - mesalazine (5-ASA) - olsalazine (5-ASA dimer linked by a bond that is hydrolysed by colonic bacteria) - balsalazide (pro-drug of 5-ASA and released following hydrolysis) A combination of oral and topical 5-ASA compounds brings patients into remission more quickly than oral therapy alone **Adverse effects** - headache, nausea, epigastric pain, skin rashes, interstitial nephritis, blood dyscrasias and hepatitis. - reversible male infertility (sulfasalazine) **Contraindications** **Other information** *Administration* - 5-ASA is absorbed when administered orally so various formulations are used to deliver the active drug (to prevent absorption) to the colonic mucosa topically so that it can reach the site of action. This can be done a few different ways eg: - combining 5-ASA with a carrier molecule (e.g. sulfapyridine to form sulfasalazine) - creating a dimer (eg olsalazine) to prevent its absorption in the small intestine. - These combination molecules are linked by a diazo ( -N=N- ) bond which is broken down by colonic bacteria to release 5-ASA. - using formulations which release 5-ASA in the distal small bowel and colon by a pH-dependent mechanism (e.g. mesalazine). - The choice of formulation for rectal administration of 5-ASA depends on the extent of active disease involvement: - suppositories can be used for limited proctitis; - foam preparations for disease extending to the sigmoid colon; - enemas for disease extending to the descending colon and splenic flexure.

Answer 109

**MoA** Corticosteroids are used for anti-inflammatory properties. They regulate gene expression, which results in: - glucocorticoid effects, e.g. gluconeogenesis, proteolysis, lipolysis, suppression of inflammation and immune responses - mineralocorticoid effects, e.g. hypertension, sodium and water retention, potassium loss. Rapid suppression of inflammation and symptoms usually within days (weighed against the significant side effect profile) Steroids can also be given topically: the formulation (suppository, foam or enema) depends on the extent of active disease as for 5-ASA. **Indications** Patients with acute flares who are either too sick for or don't respond/tolerate 5-ASA therapy oral steroids are considered. Used for moderate to severe UC **NOT** effective for maintenance therapy Crohn's For ileocaecal disease, oral budesonide, particularly for patients with a history of adverse reactions to systemic corticosteroids may be used. For mild to moderate disease oral therapy is usually adequate, however induction for severe disease may require intravenous therapy for a period. **Adverse effects** Side effects: **MANY**! Less with topical compared with systematic steroids. - psychological effects - sleep disturbance - weight gain and fat redistribution - skin atrophy - immunosuppresssion - metabolic effects - osteoporosis - GI effects - myopathy - HPA suppression - hypertension - sodium retention **Contraindications** **Other information** Budesonide is more active topically in the bowel (compared to it's systemic effect) when given orally and may offer benefit over other corticosteroids. Therapy usually requires step-down and tapering.

Answer 110

MTX **MoA** Folic acid analogue which binds to and inhibits DHFR activity. MTX impairs cell division and induces apoptosis as folic acid is essential to DNA synthesis. **Indications** **Adverse effects** **Contraindications** **Other information** Folic acid should be co-administered - though not on the same day, to reduce GI adverse effects and hepatotoxicity **Note** for thiopurines or MTX - Much more evidence for the use of thiopurines and are therefore the class of choice. - Started when disease is severe at onset - steroid-dependent - a second course of steroid for relapse is required within 12 months - patient has important reason to avoid steroids.

Answer 111

- **TNF-alpha inhibitors (infliximab and adalimumab)** - Effective and approved for both CD and UC TNFa-i **MoA** TNF-alpha antagonists (infliximab, adalimumab and golimumab). Appear to be effective with 60-70% improvement. **Indications** Effective and approved for both CD and UC **Adverse effects** **Contraindications** **Other information** Precautions - _**Infection**:_ Contraindicated in serious or untreated infection, e.g. sepsis, abscess, hepatitis B, active TB (before completing TB treatment). May reactivate inactive hepatitis B and latent TB (begin TB treatment before starting a TNF-alpha antagonist). - _**Demyelinating disorders:** e.g. MS_ — contraindicated; TNF-alpha antagonists may increase disease activity. - _**Psoriasis** **and other skin reactions:**_ up to 20% of patients on anti-TNF agents develop skin reactions including psoriasis and eczema. - _**Heart failure**:_ contraindicated in moderate or severe heart failure (NYHA class III–IV) and left ventricular ejection fraction <50%; use cautiously in mild disease as TNF-alpha antagonists may worsen heart failure. - _**Treatment with other immunosuppressants:**_ increases risk of infection; - _**History of blood dyscrasias**:_ rare cases of serious blood dyscrasias (some fatal) have been reported; monitor complete blood count regularly. - _**Respiratory disease**:_ may be at increased risk of interstitial lung disease with TNF-alpha antagonists - _**Antibodies against double-stranded DNA (eg lupus)** :_ TNF-alpha antagonists are associated with the formation of autoantibodies to ds-DNA. These may worsen or induce a lupus-like syndrome. - **_Malignancy_**: Contraindicated if there is a history of lymphoproliferative disease within the last 5 years. TNF-alpha affects cellular immune response and its inhibition may affect development of malignancies. - _**Surgery**_: Consider the risk of infection.

Answer 112

Anti-integrin antibodies eg **vedolizumab** **MoA** - **Gut-specific**, recombinant, humanised IgG1 monoclonal antibody against alpha4-beta7-integrin present on the surface of leucocytes, including T lymphocytes. - Inhibits adhesion of T lymphocytes to mucosal addressin-cell adhesion molecule‑1 (MAdCAM‑1) expressed in the GIT and _prevents lymphocyte migration into intestinal tissue_. - Slower onset of action compared with anti-TNF **Indications** Approved for both UD and DC, gut-specific targeted. Longer onset of action than anti-TNF **Adverse effects** - Favourable due to GIT selectivity - Arthralgia, headache, cough, infections, hypersensitivity reactions (may be significant) **Contraindications** **Other information**

Answer 113

**MoA** Recombinant human immunoglobulin monoclonal antibody that targets the p40 subunit on IL-12 and IL-23 inhibiting their activity. **Indications** Indicated for moderate to severe CD; well tolerated **Adverse effects** Similar Adverse effects as the other biological classes (listed above) **Contraindications** **Other information**

Answer 114

- reserved for "medical rescue" when severe disease is non-responsive to high-dose intravenous corticosteroids - Not discussed here - covered in block 6 as used for other indications

Answer 115

**MoA** Blocks D2 receptors in the chemoreceptor trigger zone (CTZ) At high doses is 5HT-3 blocker (may also block histamine and muscarinic receptors) Prokinetic (increased gastric emptying) effects on upper GIT **Indications** *Commonly used antiemetic class* **Adverse effects** - can cause acute dystonias/Parkinsonism and tardive dyskinesia or extrapyramidal side effects - **Contraindications** - avoid in PD (domperidone is a D2 antagonist, and prokinetic, that does NOT cross BBB and may be suitable in some PD patients)

Answer 116

Serotonin antagonists 5HT receptors occur peripherally in the GIT on the vagus nerve and centrally in the vomiting centre and the CTZ Useful in most causes of nausea and vomiting such as post-op, chemotherapy, etc **Commonly used antiemetic class** Side effects: Well tolerated, can prolong the QT interval

Answer 117

H1 antagonists Block histamine from activating the H1 receptor Cause drowsiness - less commonly used in practice due to drowsiness Indicated for postoperative nausea and vomiting, motion sickness and radiation-induced nausea and vomiting eg promethazine cyclizine Muscarinic antagonists Competitively blocks acetylcholine receptor (M1) in vestibular and vomiting centre Mostly used for motion sickness Anticholinergic side effects - limits use in practice, but are used if abdominal cramps are problematic hyoscine

Answer 118

eg aprepitant) Act on NK 1 receptors located through CNS and involved in pain and emetic pathways Used to treat chemotherapy-induced nausea and vomiting (usually in combination with other agents) **Relatively new agents and place in therapy is evolving

Answer 119

** ### GCs and benzodiazepines ### (usually dexamethasone) Used as part of combination therapy in oncology-related nausea and vomiting (and per-operative refractory emesis) Indicated for nausea and vomiting associated with cerebral swelling and CNS tumors usually lorazepam) Sedation and anxiolytic properties Used in anticipatory vomiting (particularly in oncological setting) Prucalopride/5HT-4 A 5HT4 receptor agonist that increases GI motility (prokinetic) used in chronic idiopathic constipation, when other regular laxatives are inadequate. Onset of laxative effect generally occurs within the first few weeks (not fast acting!) **nOTE; the usual stepwise approach to treating functional constipation in adults is as follows**: bulk forming, osmotic, stimulant, prokinetic

Answer 120

Loperamide **MoA**' Activates opioid receptors in the gut wall (no central effects) - ↓ secretions and inhibit propulsive movements in the gut - Slow the passage of intestinal contents - Allow reabsorption of water & electrolytes - ↓ stool frequency **Indications** Short term treatment - Diarrhoea - Intestinal stoma (to reduce frequency and fluidity of motions) **Adverse effects** Abdominal pain and bloating, nausea, vomiting, constipation **Contraindications** **Extra information** Codeine **MoA**' Natural occurring opioid (a pro-drug of morphine - 10% is converted to morphine in the liver) . Agonist at mu receptors in the GIT causing inhibition of peristalsis -> constipation Does also work centrally and therefore can have opioid related side effects such as drowsiness and nausea. **Indications** **Adverse effects** **Contraindications** **Extra information** Diphenoxylate **MoA**' - Inhibits intestinal propulsive motility - Acts directly on mu (μ) opioid receptors on intestinal smooth muscle - The addition of atropine acts as an anticholinergic and also to discourage abuse **Indications** **Adverse effects** Abdominal pain, nausea, vomiting, constipation, rash, dizziness and drowsiness, anticholinergic side effects (due to atropine)

Answer 121

Antacids Symptomatic based relief of excessive gastric acid secretion (directly neutralise acid) Most antacids use a combination of magnesium and aluminium salts - Magnesium salts cause diarrhoea - Aluminium salts cause constipation Antacids are faster acting when given in a fasting state Liquid and powder dosing forms tend to be more effective than tablets Antacids can reduce the effect of a number of other medicines taken by mouth. The best way to avoid a problem is to separate taking antacids and other medicines by at least 2 hours Most available without prescription (and even in the supermarket) Examples include - MgOH - - forms magnesium chloride in stomach - no systemic effects as Mg2+ is poorly absorbed from the gut .˙. local action - diarrhoea - AlOH - Forms aluminium chloride in stomach - Raises gastric juice pH to ~4 - constipation - Alginates - sometimes added to antacids - ↑ viscosity and adherence to mucus - forms protective barrier - Simethicone - sometimes added to antacids - anti-foaming agent - relieves bloating and flatulence Mucosal protective agents _Rarely used in practice_ Sucralfate: aluminium salt – forms protective barrier at ulcer site resistant to acid, bile and pepsin Misoprostol: prostaglandin E1 (PGE1) analogue; stimulates secretion of gastric mucus and bicarbonate in the duodenum and decrease in gastric acid secretion by parietal cells Bismuth subcitrate: no longer marketed in Australia. Forms an acid‑ and pepsin-resistant protective coating at the ulcer site; also has an antibacterial effect against _H. pylori_

Answer 122

Varices - Why Are They Important? - Most (80%) cirrhotics will develop varices. - Main cause of upper GI bleeding in cirrhosis (peptic ulcer, other causes less often). - High mortality from bleed and rebleed (SCREEN ALL CIRRHOTICS). - use platelet count, liver stiffness measurements i.e. fibroscan to screen Management Plan - **Prevent**: *Prevent bleeding* through banding or drugs that lower portal pressure (propranolol, **carvedilol** - beta blocker with alpha blocking action, may be useful in liver specifically). ^[avoid non-selective drugs in asthmatics] - **Bleeding**: *Treat bleeding* with banding + drugs that lower portal pressure (octreotide IV/infusion - somatostatin analog). - **Prevent Re-Bleeding**: Prevent re-bleeding through banding. Managing Acute Bleeding - Bleeding can be SEVERE. - Protect airway e.g. intubation, aim for Hb 80 g/L. - Administer antibiotics and lactulose. - SBP (Spontaneous Bacterial Peritonitis) and encephalopathy are common after a bleed. - Antibiotics also reduce rebleeding risk. - Start octreotide (reduces splanchnic flow). - Endoscopy ##### Endoscopic Variceal Ligation (EVL) - EVL is 90% effective for control of acute bleeding.- done monthly until all variceal columns targeted Alternatives to Endoscopy - If endoscopy fails: - **Balloon Tamponade**: Sengstaken-Blakemore tube – OCCLUDE varices. - **Transjugular Intrahepatic Portosystemic Shunt (TIPS)**: DIVERT BLOOD. - **Surgery**: Very rare now.

Answer 123

Hepatic Encephalopathy - **Impaired neuropsychiatric syndrome** due to acute or chronic liver disease - Hepatic encephalopathy in essence: ammonia intoxication as a result of portal shunting to brain, altering mental state - ammonia end-product of protein metabolism in intestine, due to bacteria - shunted to liver, normal de-toxxed to urea and excreted - **Grades** I (mild confusion, non-specific, poor sleep, 'night watchman- awake at night, asleep in day') to IV (coma) - **FLAP**/**Asterixis** - more prominent in GII/III - unlikely in GI - neuropsychiatric symptoms worsens in III - **STROOP TEST**/psychometric number connection tests (timed test) - can be used to check response to treatment - **Remember!** - There are other causes of confusion: SDH, sedating drugs and meds, hyponatremia, hypoglycaemia, withdrawal delirium from alcohol or Wernicke's Hepatic Encephalopathy - Management - **Treat precipitating factors** (infection, drugs, constipation, hypokalaemia, GI bleeding) -> helps improve encephalopathy - **Lactulose** (MAIN STAY) - How does it work? - Acidifies gut (reduces ammonia) - Inhibits ammonia-forming bacteria - Acts as a laxative - **Antibiotics**: Sterilize gut - if not responsive to lactulose - Rifaximin - Metronidazole - Neomycin (historical) - combination of lactulose and antibiotics may be useful, eg if lactulose poorly tolerated ie patient becomes bloating

Answer 124

**CYP enzymes - CYP enzymes responsible for Phase 1 (functionalisation) metabolism - CYP enzymes found in the smooth endoplasmic reticulum - Abundant in hepatocytes - More than 50 varieties. Three main families - Genetic polymorphisms occur altering clearance of particular medications - Responsible for many drug interactions - Liver disease can effect the performance of these enzymes **Hepatic clearance** - Depends on hepatic blood flow (Q) and extraction ratio (EH) - Hepatic extraction ratio (EH): - the fraction of drug entering the liver in the blood that is irreversibly removed by metabolism on each pass through the liver. (0.7 = 70% removed) - Hepatic clearance (Cl) = Q. EH - Hepatic clearance can be: - low extraction: - clearance capacity by limited by liver enzymes to clear drug (clearance is independent of blood flow) - high extraction - clearance capacity limited by delivery of drug to the liver (blood flow)

Answer 125

- **Mastication (Chewing):** - Breaks up large pieces of food - Mixes food particles with saliva to form a bolus, to facilitate swallowing and digestion - Optimal number of chews: 20 - 25 - **Swallowing:** - Note oesophageal sphincter closes; epiglottis goes up, uvula goes down to ensure food goes the right way - Primary peristalsis initiated by act of swallowing - Secondary peristalsis initiated by distension of oesophagus - flush out any potential reflux - On average, bolus takes 10 s to reach stomach

Answer 126

Stomach *Gastric functions & secretions* - **Motor function:** - Regulate food intake - Mixing with secretions - Reduction in particle size by grinding - Empties chyme into duodenum - Liquids - proximal part - Solids - antral part - **Secretions:** - Acid - Pepsinogen - Mucus - Bicarbonate - Intrinsic factor - H2O **Gastric Filling** - Three types of stomach relaxations: 1. Receptive relaxation - triggered by swallowing 2. Adaptive relaxation - distension (filling) 3. Feedback relaxation - triggered by nutrients in small intestine - ensure all food making its way out - ENS is the primary regulator of gastric accommodation - Vagus nerve plays a modulatory role - note: Increase in intragastric volume without increase in pressure - accommodates more food - as pressure builds: satiety - hence **Gastric Banding**, see also [[Gastroenterology - Lecture 19]] **Gastric Emptying:** - Saline and water empty first - Acidic and caloric fluids more slowly - Fatty material even slower - Solids must be reduced to less than ~ 2 mm - hence lag for solids - Three distinct phases: Propulsion, Grinding, Retropulsion - propulsion: gastric contractions propel food towards antrum (initiated by gastric pacemaker). Pyloric valve is closed - grinding: chyme is churned in the antrum by propulsion. Pyloric valve is closed - helps to slam food, breaking down particles - retropulsion: most of chyme will not go through and is returned to stomach. Pyloric valve is slightly open - process cycles **Delaying Gastric Emptying** - Volume of liquid in stomach is of primary importance (emptying rate proportional to volume i.e. bigger volume quicker empty) - Receptors in small intestine and duodenum monitor the fluid leaving the stomach. - Low **pH - High **caloric content - **Lipid - Some **amino acids - **Osmolarity - all of the above Trigger a *delay in gastric emptying via neural & hormonal signals* (listed below): - This happens by: Fundic relaxation, Decrease in antral motor activity, Contraction of pyloric sphincter, Altered intestinal motor activity - via: - Vagus nerve - Secretin - Cholecystokinin - Gastric inhibitory peptide

Answer 127

**Carbohydrate Digestion** - Substrate is dietary CH2 O (starch from plants, glycogen from animals) - Amylase hydrolyzes α1,4 glycosidic linkages in polysaccharides - Cellulose is a polysaccharide (poly-glucose) but joined in β1,4 links. No animal enzyme can cleave them. (Bacterial cellulase in ruminants) - Result is a mixture of trisaccharide (maltotriose) + disaccharide (maltose) α-limit dextrin (branched oligosaccharide with α1,6 bonds) - - Salivary amylase may hydrolyze up to 25% of total starch in diet. **Carbohydrate Digestion - 2** Following digestion by salivary and pancreatic amylase, there is a mixture of oligo- and di-saccharides. These are metabolized by disaccharidases located in the brush borders of the intestinal enterocytes. The end result is the production of monosaccharides, which can be absorbed by the intestinal mucosa. For persons on a normal diet, glucose accounts for approximately 80% of the final monosaccharides available for absorption. ![[Pasted image 20240501084654.png]] - lactose ---> glucose and galactose - maltose --> 2 glucose - sucrose ---> glucose and fructose Glucose is absorbed in association with sodium (3Na/2K, makes intracellular environment more negative, which drives passive Na/glucose symporter -- which also transports galactose. Absorbed into blood by glucose/fructose transporters). See also [[Physiology B5 - Lecture 4]] Firstly sodium is transported from the intestinal epithelial cell into the blood. Secondly, in response to reduced epithelial cell sodium, sodium is absorbed from the intestine by facilitated diffusion, bound to a transport protein. This transport protein will not move into the cell without glucose. Galactose is absorbed in similar fashion to glucose. Fructose is absorbed by facilitated diffusion via a sodium- independent process. Carbohydrates Only glucose, galactose and fructose are well absorbed (mostly in duodenum and proximal jejunum) Intestine has the capacity to transport 3.6 kg glucose/day **Monosaccharide transporters** - SGLT1 AND GLUT5 for Na/glucose/galactose, fructose respectively on apical surface, GLUT2 on basolateral membrane - gradient driven by 3Na 2K ATPase - **Carbohydrate malabsoprtion syndromes** Most are a result of a deficiency in carbohydrate digestion (e.g. lactose intolerance) But not all.. Glucose-galactose malabsorption syndrome (very rare hereditary disorder) Missense mutation in SGLT1

Answer 128

**Lipid Digestion (1)** - 90% of dietary fat is triglyceride (TG), with the remainder being cholesterol, cholesterol ester, phospholipid, and free fatty acids (FFA). - The primary site of lipid digestion is in the duodenum, requiring fat to be highly emulsified with bile salts and lecithin. - (TAG) Lipase released from the pancreas hydrolyzes TG to monoglycerides and FFA, requiring co-lipase for activity. - Co-lipase binds to water-lipid interface (on globule surface, of micelle) and simultaneously activates lipase **Lipid Absorption** - Absorption occurs in the jejunum, where micelles deliver lipid digest to the brush border. - FFA eg glycerol and 2-mono-acylglyceride (MAG) are taken up into enterocytes by diffusion because they are lipid-soluble. - 2MAG used for re-synthesis of TAGs, by fatty acid CoA ligase, using long chain fatty acids - Within enterocytes, absorbed FFA are converted predominantly to triglycerides, which are released into thoracic duct lymph as chylomicrons -- for long chain FAs. - Some short chain fatty acids are absorbed directly into portal blood **Lymphatics** - The lymphatics drain excess fluid and secretions from the interstitial spaces. - Especially important is the ability to carry proteins, large molecules, and particulate matter from tissue spaces. - Lymphatic drainage from the gut empties into the thoracic duct, which drains into the left internal jugular vein at the junction with the left subclavian vein. Lipid entry into the unstirred layer - Small fatty acids penetrate unstirred water layer and are absorbed - Effective concentration of long chain fatty acids adjacent to brush border is increased by a factor of 0.1 - 1 million by micellar solubilisation ### Lipid absorption - TAGs are emulsified and form micelles - pancreatic lipase and colipase results in monoglycerides and FFAs mainly by diffusion, some facilitated diffusion or active transport - cholesterol is transported, but some diffused - TAGs reconstituted in cells, fats and cholesterol and proteins to form chylomicrons which go to lymph to vena cava (Too big to enter capillaries) - note choelsterol is 'kicked out' by some channels

Answer 129

**Protein Digestion - 1** - The total protein load in the gastrointestinal tract per day is: - Dietary: 70 - 100 g per day (adult) - Endogenous: 35 – 200 g (enzymes, other proteins, cell turnover). - Digestion is efficient, usually resulting in only 6-12 g of protein in feces. - Two types of proteolysis are described: - Trypsin and chymotrypsin split proteins into smaller peptides. - Carboxypeptidase cleaves proteins to individual amino acids. - The net end products are amino acids, di- and tri-peptides. - Sites of action of the peptidases are very specific e.g. chemotrypsin and hydrophobic pocket (Phe), trypsin and salt bridges (Lys), elastase small hydrophobic pocket (Gly) **Protein Digestion - 2** - Proteases (peptidases) are generally secreted into the lumen in an inactive form. - The active form is produced either by a pH change (e.g., pepsinogen B) or by HCl itself (pepsinogen A) in the stomach. Pancreatic trypsinogen needs duodenal entero-peptidase or (-kinase). - Trypsin’s central role is the activation of other pancreatic peptidases. (See also [[Gastroenterology - Lecture 10]] - Notably, trypsin inhibitor is secreted in the pancreas in concert. - HCO3– is important for optimal protease activity. - Membrane-bound endopeptidases, dipeptidases, and aminopeptidases convert peptides to amino acids. - Absorption of amino acids by very specific carriers (similar in renal tubular epithelium). Proteins are generally digested into peptides and amino acids before they are absorbed Six major amino acid transporters in small intestine (transport the L in preference to the D forms) **Amino acid and peptide transporters** - H/di and tripeptides, Na/AA and endocytosis - dipeptide transport most efficient - Na co transport most common

Answer 130

** - Endocrine (Islets of Langerhans) - Exocrine (acini in lobules-> interlobular ducts into main duct) which drain into the duodenum at ampulla of Vater and the accessory duct - inactive forms of enzymes stored into zymogen granules in acinar cells - duct epithelial cells release HCO3, electrolytes; lots of mitochondria

Answer 131

Carbohydrate regulation - **Fed**: BSL high. Insulin release. Stimulates glycolysis, glycogenesis, down-regulates gluconeogenesis. - **Fasted**: BSL low. Glucagon release. Stimulates glycogenolysis, gluconeogenesis, down-regulates glycolysis, switches off glycogenesis.

Answer 132

- **Environment:** - Drugs active in hydrophobic environments like tissues, cells, and membranes. Excretion is hydrophilic in bile or urine. - **Detoxification Phases:** - **Phase 1:** Oxidation, usually by Cytochrome P450. - **Phase 2:** Conjugation, including glucuronidation and sulfation. - **Influences:** - Genetic polymorphisms- leading to variability in expression - enzyme induction, age, disease, competition.

Answer 133

The tract is as follows: Bile acid synthesis occurs in liver cells, which synthesize primary bile acids (cholic acid and chenodeoxycholic acid in humans) via cytochrome P450-mediated oxidation of cholesterol in a multi-step process. Bile canaliculi >> Canals of Hering >> intrahepatic bile ductule (in portal tracts / triads) >> interlobular bile ducts >> left and right hepatic ducts[4] These merge to form the common hepatic duct[4] The common hepatic duct exits the liver and joins with the cystic duct from gall bladder[4] Together these form the common bile duct which joins the pancreatic duct[4] These pass through the ampulla of Vater and enter the duodenum[4]

Answer 134

* Immune cells in the liver: Kupffer cells (macrophages). Phagocytose. Remove antigen- antibody complexes. * Liver NK/T cells: non-specific cell killing, anti- tumour effects Theory that non-specific (MHCI) presentation in the liver leads to tolerance.. (? -- theories being developed

Answer 135

Motility/**Motor Activity** - **Musculature:** Two layers of smooth muscles, circular and longitudinal - **Motor Activity:** Peristaltic contractions (propulsive), Segmental contraction (mixes food, no propulsion), Sphincter control (retains contents in stomach and large intestine) - all are achieved by smooth muscles

Answer 136

- **Tonic and Rhythmic Contractions:** - Tonic: Sustained contractions - Rhythmic: Alternating contraction and relaxation - slow wave activity; cycles of depolarisation and repolarisation - **Function of Vm:** Intrinsic slow-wave activity (-65 to -45 mV), Action Potential (increase in muscle tension) - **key channels in slow wave**: VGCC(K moves out -- hyperpolarisation -- closes VGCC -- Ca decreases -- K channels close, depolarising, VGCC opens, and K channel (iCa-dependent)

Answer 137

Mastication & Swallowing - **Mastication (Chewing):** - Breaks up large pieces of food - Mixes food particles with saliva to form a bolus, to facilitate swallowing and digestion - Optimal number of chews: 20 - 25

Answer 138

- **Swallowing:** - Note osophageal sphincter closes, epiglottis goes up, uvula goes down to ensure food goes the right way - Primary peristalsis initiated by act of swallowing - Secondary peristalsis initiated by distension of oesophagus - flush out any potential reflux - On average, bolus takes 10 s to reach stomach **Esophageal Sphincters** - **Upper Esophageal Sphincter:** - Striated muscle - potential to gain control - Highest resting pressure of all sphincters in GI tract - Under control of swallowing centre in medulla **Lower Esophageal Sphincter** - Smooth muscle - Opens when swallowing begins - synchronous - Tonically active (prevents reflux) but relaxes upon swallowing - Under control of the vagus nerve (contract) and intrinsic properties of smooth muscle (release of NO and VIP causes relaxation). **Swallowing** - Contraction is strongest and fastest during oropharyneal phase - UES and LES relax simultaneously - LES contracts after UES contraction i.e. stays relaxed until food has passed - Vomiting - anti-peristalsis

Answer 139

Secretions:** - Acid - Pepsinogen - Mucus - Bicarbonate - Intrinsic factor - H2O

Answer 140

**Gastric Filling** - Three types of stomach relaxations: 1. Receptive relaxation - triggered by swallowing 2. Adaptive relaxation - distension (filling) 3. Feedback relaxation - triggered by nutrients in small intestine - ensure all food making its way out - ENS is the primary regulator of gastric accommodation - Vagus nerve plays a modulatory role - note: Increase in intragastric volume without increase in pressure - accommodates more food - as pressure builds: satiety - hence **Gastric Banding**

Answer 141

**Delaying Gastric Emptying** - Volume of liquid in stomach is of primary importance (emptying rate proportional to volume i.e. bigger volume quicker empty) - Receptors in small intestine and duodenum monitor the fluid leaving the stomach. - Low pH - High caloric content - Lipid - Some amino acids - Osmolarity - all of the above Trigger a delay in gastric emptying via neural & hormonal signals: - This happens by: Fundic relaxation, Decrease in antral motor activity, Contraction of pyloric sphincter, Altered intestinal motor activity - via: - - Vagus nerve - Secretin - Cholecystokinin - Gastric inhibitory peptide see gastric acid secretionand regulation for part a

Answer 142

- Secretin: secreted by S cells in mucosa of duodenum in response to pH, Inhibitory effect on motility of most of GI tract, Stimulates secretion of bicarb from pancreas and liver.

Answer 143

- Cholecystokinin (CCK): Secreted by I cells in mucosa of duodenum and jejunum mainly in response to fat breakdown products, Moderately inhibits stomach motility, **Potently increases contraction of gallbladder.

Answer 144

- Gastric inhibitory peptide (GIP): Secreted by K cells in mucosa of the proximal small intestine in response to macromolecules i.e.. fatty acids, AAs, and carbohydrates; Moderately inhibits stomach motility, Prevents overloading of small intestine.

Answer 145

Electrolytes** - Na and Cl are net absorbed by SI and LI - K is secreted by LI and absorbed by SI (net) - HCO3 is net secreted by SI and LI Na+ Absorption** - Na+/nutrient cotransport - primary mechanism - Na is transported by either Na/glucose or Na/AA symporters - gradient/absorption is by 3Na-2K-ATPase - mechanism is electrogenic - primarily occurs in jejunum, moderate amount in ileum - Na+/H+ exchange - Na/H exchangers 2 and 3 on apical surface (amiloride works here in mM doses) - another exchanger NHE1 helps to regulate pH of cell - 3Na-2K-Atpase imports Na/helps establish gradient - Na/H exchanger activity stimulated by luminal alkalinity - mechanism is electroneutral - mainly occurs in jejunum, moderate amount in duodenum - Na+/H+ & Cl-/HCO3- exchange - NHE and Cl/HCO3 exchanger on apical surface - CO2 diffuses into cell, with water - water splits into H and OH - H is exchanged for Na - OH combines with CO2 catalysed by CA to form HCO3, which is secreted out - Cl leaks out via transporters - 3 Na/2K ATPase helps establish gradient - this is Primary mechanism of Na+ absorption between meals - Results in electroneutral absorption of NaCl - Diminished activity results in diarrhea - happens in both ileum and proximal colon - Epithelial Na+ channels - ENaC on apical surface, 3Na-2K-ATPase on basal surface - occurs in distal colon - electrogenic Na absorption - amiloride acts here in uM doses **Cl- Absorption** - Passive - Occurs paracellularly - Small intestine - jejunum and ileum - facilitated by electrogenic Na process (nutrient co-transport) - Large intestine - distal colon - facilitated by electrogenic Na process (ENaC) - Cl-/HCO3- exchange - same process as Na/H/Cl/HCO3 -- with Na/H on basolateral membrane (transporting H from splitting water) - - NHE and Cl/HCO3 exchanger on apical surface - CO2 diffuses into cell, with water - water splits into H and OH - H is exchanged for Na - OH combines with CO2 catalysed by CA to form HCO3, which is secreted out - Cl leaks out via transporters - 3 Na/2K ATPase helps establish gradient - this is Primary mechanism of Na+ absorption between meals - Results in electroneutral absorption of NaCl - Diminished activity results in diarrhea - happens in both ileum and proximal colon - mainly proximal colon, also ileum and distal colon - Na+/H+ & Cl-/HCO3- exchange - see above - proximal colon and ileum **Cl- Secretion** - Involved in the pathophysiology of many types of diarrhea (bacterial enterotoxins, certain intestinal tumors (↑ VIP production), laxatives) - occurs all along SI and LI - insertion of pre/made Cl channel at apical surface - cAMP nad Ca enhance this process - also encourages Cl channels to be more open, increases 2 types of K channels at basolateral surface, driving 3Na-2K-ATPase, making Na concentration low in the cell, driving NA/K/2CL ATPase driving Cl out to lumen **K+ Secretion/Absorption** - Intestines have capacity for K+ absorption and secretion - Net absorption in small intestine - Net secretion in large intestine ### Passive K+ transport - absorption occurs via solvent drag i.e. paracellularly - jujunum and ileum - secretion - paracellular - main pathway responsible for net K secretion in colon - net negative charge in lumen generated by Na movement through Na channel (3Na 2K ATPase) - distal colon mainly, also proximal colon Active K+ transport - absorption - H/K exchanger, gradient driven by 3Na 2K ATPase - leaves into blood by K channels on basolateral surface - distal colon - secretion - same as Cl secretion process - K leaves via channels on apical surface - 3Na-2K-ATPase, making Na concentration low in the cell, driving NA/K/2CL ATPase driving Cl out to lumen - mainly proximal colon, also distal colon

Answer 146

**Oral Rehydration Solution (ORS)** - Takes advantage of sodium and glucose transport in small intestine. - Water is taken up osmotically after sodium entry. - Potassium is then absorbed via solvent drag (paracellular). - Sodium concentration can be varied depending on degree of dehydration.

Answer 147

**Cl- Secretion** - Involved in the pathophysiology of many types of diarrhea (bacterial enterotoxins, certain intestinal tumors (↑ VIP production), laxatives) - occurs all along SI and LI - insertion of pre/made Cl channel at apical surface - cAMP nad Ca enhance this process - also encourages Cl channels to be more open, increases 2 types of K channels at basolateral surface, driving 3Na-2K-ATPase, making Na concentration low in the cell, driving NA/K/2CL ATPase driving Cl out to lumen

Answer 148

** - Approximately 1.5 L secreted/day (pH 7 (basal) - pH 8 (stimulated i.e. when eating)) - Contains two digestive enzymes: lingual lipase (glands on tongue ) and salivary amylase (Salivary glands) - Also contains mucins to lubricate food and facilitate swallowing, lysozyme which breaks down bacterial cell wall, lactoferrin binds iron and is bacteriostatic, and **proline-rich proteins - protect teeth and bind tannins** - Acts as a solvent and lubricant, facilitating taste and speech respectively **Position of Salivary Glands** - Parotid glands (25% watery secretion) - Submandibular glands (70% mixed secretion: mucous and water) - Sublingual glands (5% viscous secretion)

Answer 149

- salivon unit that secretes - acinus secreted into - divided by intercalated duct - straited duct carries out into mouth - can change content of saliva along length eg more water, K HCO3, less Na Cl - serous cell: watery secretion - electrolytes and salivary amylase - mucuous cell: mucin **Salivary-duct transporters** ![[Pasted image 20240430205551.png]] - key transporters include - in duct **not acinus**: - H/K ATP-ase - K out, H in - regulated by iCa and M3 (Ach) - CL/HCO3 exchanger - REABSORB cL - reabsorbed via Cl channels, HCO3 secretion - NA- h atpase -> Na/K ATPase (reabsorb Na) - note lumen is impermeable to water **Electrolyte composition of saliva** - osmolarity increases with rate of secretion - Na, HCO CL up - k GOES DOWN - not enough time for Na Cl to be absorbed - HCO3 going up to bring pH up ?

Answer 150

**Acid Secretion** - Mediated by HK ATPase: P-TYPE ATPases (H swapped for K, from splitting water, so OH and Co2 makes HCO3 swapped out for Cl; Cl goes into lumen along gradient; K along gradient in or out) - juice: Cl and H increases with secretory rate; K (related to pump) and Na goes down **Acid secretion regulation** - Regulated by three secretagogues: acetylcholine, gastrin, and histamine - Ach and gastrin act directly and indirectly - Histamine acts directly - Ach binds M3- induces histamine release from ECL cells to promote H, and Ach binding M3 directly induces H from parietal cells - Gastrin promotes Histamine release from ECL cells and H directly from parietal cells - note omeprazole directly binds HK ATPase - antihistamines can bind H2 to reduce acid secretion - Somatostatin acts as a major inhibitory mechanism - made by D cells in corpus and antrum - 2 forms, SS-14 and 28 - Direct pathway: binds SS receptors on parietal cells to inhibit the stimulatory effect of histamine; acts endocrine via D CELLS OF ANTRUM OR paracrine via D cells in corpus - Indirect pathway: **Paracrine**; acts in corpus to reduce histamine release from ECL cells, and in antrum reduces gastrin release from G cells **Phases of Gastric Acid Secretion** - Acid secretion follows basal state and three phases during a meal: cephalic, gastric, and intestinal 1. Basal state: Inter-digestive phase, H+ secretion takes place 24/7 - follows circadian rhythm: lowest in morning highest in evening - H+ secretion is associated with parietal cell number - high varaibility in basal state pH (3-7) 2. Cephalic phase: Activated by sight, smell, taste, thought, and swallowing of food. Vagus plays main role. 30% of acid secretion - starts happening before food reches stomach - four distinct phases - Direct stimulation of parietal cells(acetylcholine mediated) - Release of histamine from ECL cells(acetylcholine mediated) - Release of gastrin from G-cells(gastrin-releasing peptide mediated) - Decrease in somatostatin release from D-cells (acetylcholine mediated) 3. Gastric phase: Stimulated by distention of gastric wall and partially digested proteins. Gastrin release in main role. 50-60% of acid secretion - Entry of food in stomach causes two stimuli for H+ secretion - Distention of gastric wall (corpus and antrum) - Activates Vagovagal reflex(same response as that seen in cephalic phase) - Activates local ENS reflex (Ach mediated activation of parietal cells) - Partially digested proteins (peptones) stimulate G-cells in antrum to release more gastrin 4. Intestinal phase: Stimulated by peptones and amino acids in proximal small intestine. 5-10% of acid secretion - Peptones stimulate G-cells in duodenum - gastrin release - An ‘entero-oxyntin’ stimulates parietal cells - Absorbed amino acids stimulate acid secretion by an unknown mechanism -

Answer 151

Vitamin B12 Absorption** - vitamin B12 ingested in food - salivary glands secrete haptocorrin - acid in stomach releases vitamin B12 from food - haptocorrin binds released vitamin B12 in stomach - stomach parietal cells secrete intrinsic factor - pancreatic proteases digest haptocorrin in small intestine releasing B12 - vitamin B12 binds to intrinsic factor in the small intestine - vitamin B12 intrinsic factor complex is absorbed in the terminal ileum

Answer 152

**Pepsinogen Secretion** - Multiple pepsinogens are secreted by Chief cells - Initiate protein digestion as aspartic proteases - Released as zymogens by ‘compound exocytosis’ (i.e. vesicles fuse and then exocytose) - secretin and other compounds act via cAMP - Ach, gastrin/CCK act via increased intracellular Ca concentration **Pepsin Activation** - Small N-terminal fragment needs to be cleaved to become active - pH < 5 - note at lower pepsin catalyses reaction to make more pepsin - Optimal activity pH: 1.8 - 3.5 - pH > 7.2 irreversibly inactivates the enzyme - a protective feature to ensure SI cells are protected from degradation

Answer 153

**Intestinal Factors Reducing H+ Secretion** Intestinal chyme during gastric phase inhibits gastric acid secretion- Reverse Enterogastric Reflex - Purpose is to slow down release of chyme from stomach 1. Transmitted through ENS and Vagus nerve - Initiated by: stretch, pH, peptones 2. Mediated by intestinal hormones - Initiated by: pH, fat, peptones & osmolarity - Mainly Secretin but also GIP, VIP, and SS -

Answer 154

**Pancreas** - **Anatomy** - Endocrine (Islets of Langerhans) - Exocrine (acini in lobules-> interlobular ducts into main duct) which drain into the duodenum at ampulla of Vater and the accessory duct - inactive forms of enzymes stored into zymogen granules in acinar cells - duct epithelial cells release HCO3, electrolytes; lots of mitochondria - **Secretions** - Water, electrolytes and bicarbonate to neutralize the acid secretions from the stomach - Enzymes to metabolize protein, carbohydrate and fat **Pancreatic Secretion** - Signals for release of pancreatic contents are primarily: - Secretin: Secreted when food, esp. acid, enters duodenum - from duodenal and jejunal mucosa - Secretin stimulates pancreatic ductal epithelium to secrete large quantities of water and sodium bicarbonate to neutralize gastric acid - Cholecystokinin (CCK): Secreted when food (fat and amino acids) enters duodenum - from duodenal and jejunal mucosa - CCK stimulates pancreatic acinar cells to secrete digestive enzymes - Note: Pancreatic secretion is also mediated by vagal stimulation: releases enzymes into acini **Control of pancreatic enzyme activation and autodigestion in acinar cells** * Proteins exist as proenzymes or zymogens * Proteins sequestered in secretory granules – membrane is impermeable to proteins - avoid digestion of intracellular contents * Proteins stored with inhibitors * Conditions in secretory pathway inhibit enzyme activity

Answer 155

BD - Crohn’s vs Coeliac vs UC Irritable bowel syndrome (IBS) - recurrent abdominal pain 1+ days per week in the last 3 months associated with one of the following 1) related to defecation, 2) stool frequency change (constipation or diarrhoea) 3) stool consistency change. Lecturer– alternating constipation/diarrhoea. Lower abdominal cramping. Bloating/distension. Passage of mucous. Can often be controlled with diet, stress management and medications IBD – encompasses many other conditions - below CROHN’S DISEASE Can affect any area of GIT (unlike UC) Immune related – immune system triggered by foreign pathogen in GIT. Unregulated/dysfunctional inflammation response results in tissue destruction. Thought to be genetic (NOD2 gene frameshift mutation) Histopathology – granuloma, ulcer formation Transmural inflammation (during entire depth of intestinal wall, mucosa -> serosa). Scattered areas of inflammation (not continuous). Symptoms – diarrhoea (loss of ability to absorb water) + blood in stool. If SI affected, malabsorption issues. Treatment – anti-inflammatory medications and antibiotics (control gut bacteria and reduce immune response). Severe symptoms -> immunosuppressants. Removal doesn’t cure. ULCERATIVE COLLITIS Forms ulcers along inner surface of large intestine, including both colon and rectum Only affects mucosa and submucosa (not deeper layers) Autoimmune in origin – caused by T cell destroying walls of large intestine, leaving behind ulcers. Precise mechanism/reason unknown. Inflammation is circumferential and continuous Symptoms – left lower quadrant pain, diarrhoea (can’t absorb water, can be with or without blood) Diagnosis requires colonoscopy. Treatment depends on symptoms – anti-inflammatory (mesalamine), immunosuppressants, biologics as last resort. Colectomy as very very last resort.

Answer 156

Bilirubin is a waste product produced by the breakdown of red blood cells. Bilirubin is the end-product of heme metabolism; the liver is the site for bilirubin metabolism. Hemoglobin is broken down into heme, which is converted to biliverdin, and finally into unconjugated bilirubin (which is not water-soluble). In the bloodstream, unconjugated bilirubin binds with serum proteins—most commonly albumin. The unconjugated bilirubin is then taken up by the liver. In the liver, the unconjugated bilirubin is bound to glucuronide by the enzyme uridine 5’-diphospho-glucuronosyltransferase (UDP) and becomes conjugated bilirubin. Conjugated bilirubin is then excreted in bile. In the intestines, bacterial enzymes hydrolyze conjugated bilirubin to release free, unconjugated bilirubin, which is reduced to urobilinogen. Urobilinogen, bound to albumin, is then excreted in urine. In the intestines, some urobilinogen is converted to stercobilinogen and excreted in the stool. Thus, in normal urine, only urobilinogen is present; in normal stool, only stercobilinogen is present.

Answer 157

- biliary canaliculi draining into branches of bile ducts - heaptic arteriole coming from brnach of hepatic artery - barin of heaptic portal vein draining into central venule or central vien

Answer 158

AE enterl BCD blood serum bodily including vertical transmission

Answer 159

- **IgM-anti-HAV - **HBsAg - **Anti-HCV

Answer 160

## Footnote note some PR indications: altered bowel, lower abdo pelvic pain or acute abdo, PR bleeding + malaena, anal pain, external rectal lesions, male lower urinary symptoms, prostatic sumptoms, rectal cancer

Answer 161

fever anorexia unexplained weight loss per rectal bleeding flamily hsitory (chronic t course...)

Answer 162

- ASUC or fulminant colitis, toxic megacolon - perinanal: fissuere, absecess, fistulae; malabsorption, nutrition; colorectal cnancer

Answer 163

- average risk every 2 years, 50-74 - only 3% of positives - IfFOBT - colonoiscpy for surveillance: family hsitory, familial conditions, previous cancer or polyps/symptoms

Answer 164

Present: haematemesis, malaena, shock, PR bleed, anaemia, positive FOB - - - age over 65 - IHD - shock on admssion - CLD - ascites - continued bleeding or rebleeding - anaemia (Hb< 8) not alcoholism, PUD, NSAIDs, hepatomegaly ## Footnote mgmt by resus, assesemtn of risk, fbc clot X match, EUC, ECG, ENDO, MED THERAPY, SURG -- also ascites

Answer 165

- upper Gi most fcommon: peptic ulver then oeso, varices, gastroduodenal erosion - jujunal ileeal diverticulae rare - large borwel: andiodysplasia= diverticular disease, then carcioma/polp, Ibd each 5%