GI Revision Flashcards
What are the abdominal wall layers?
Skin Campers fascia (fat) Scarpers fascia (fibrous) External oblique Internal oblique Transverse abdominis Transversalis fascia Parietal peritoneum
What level is the coeliac trunk?
T12
Which organs are secondary retroperitoneal?
Pancreas
Duodenum
Colon - asc and desc
What is the sympathetic innervation to the gut and its effect?
Greater, lesser and least splanchnic nerves
Vasoconstriction
What is different about abdominal sympathetics?
Do not synapse at the sympathetic trunk
What is the PS innervation to the gut and its effect?
Vagus n - to 2/3 TC
Pelvic n - to anal canal
Innervate SM, HCl secretion, ACh and GRP.
L vagus nerve becomes ______
R vagus nerve becomes _______
L - anterior
R - posterior
What are the roots of greater, lesser and least splanchnic nerves?
T5-9
T10-11
T12
What is another name for the submucosal plexus?
Meissner’s
What is another name for the myenteric plexus?
Auerbach’s
What are the 2 groups of hormones in the gut?
Gastrin - gastrin + CCK
Secretin - secretin + gastrin inhibitory peptide
Which cells secrete CCK, where are they, what are they stimulated by?
I cells - duodenum + jejunum
Fat and protein in lumen
What is the role of secretin?
Increases HCO3- from pancreas
Decrease gastric acid secretion
Neutralise chyme
What is the effect of gastrin inhibitory peptide?
Increase insulin
Decrease gastric acid secretion
When might there be gut motility issues?
Hirschsprungs disease - no enteric plexus
Paralytic ileus - after surgery
Greater omentum is formed from the ________.
Dorsal mesentary
Lesser omentum is formed from the __________.
Ventral mesentery
Which organs have a dual blood supply?
Pancreas + duodenum - CT and SMA
What happens in reversed rotation in midgut development?
One rotation clockwise
TC posterior to duodenum
What happens in incomplete rotation?
only 1 90 degree rotation - left sided colon as caudal limb returns first.
What are the risks of midgut defects?
Volvulus
SMA compress TC
Subhepatic caecum
What is the difference between omphalocoele and gastroschisis?
Omphaloceole - incomplete physiological herniation, not isolated condition, amnion covering.
Gastroschisis - failure of abdominal wall, isolated.
Bowel exposed to amniotic fluid.
What is formed from ventral mesentery?
Lesser omentum
Falciform ligament
During midgut development, which limb returns to the cavity first?
Cranial
What are 3 remnants of the yolk sac?
Vitelline cyst
Vitelline fistula
Meckel’s diverticulum
What is the anal canal derived from?
Endoderm
Ectoderm - proctodeum
What is the difference between above pectinate line and below pectinate line?
Above - splanchnic innervation, stretch only. columnar ep. IMA.
Below - somatic innervation - pain, temp, touch. Strat squamous. Pudendal A.
What are the 4 narrow points of oesophagus?
Junction of oes with pharynx
Aorta crosses
L main bronchus crosses
Through diaphragm
What are 5 mechanisms preventing reflex?
- LOS
- Diaphragm surrounds and pinches
- Intra-abdominal oesophagus compressed when intra-abdominal pressure rises
- Acute angle of entry- flap-valve crosses oesophagus
- Mucosal rosette at cardia - folds prevent pressure rise
What cells are in gastric pits?
Mucous neck cells Chief cells Parietal cells D cells ECL cells G cells
What do chief cells secrete?
Pepsinogen
How is HCl secretion inhibited?
pH drops as food leaves stomach
Activates D cells - somatostatin inhibits G cells.
Reduced distention - less vagal stimulation.
What are the 3 phase of digestion?
Cephalic
Gastric
Intestinal
What happens in the cephalic phase of digestion?
PS stimuli - smelling, tasting, chewing
Vagus nerve stimulates parietal cells -> G cells stimulated.
Slight increase in gastric motility
30% HCl
What happens in the gastric phase of digestion?
60% HCl
Distension of stomach stimulates vagus nerve
AA + peptides stimulate G cells
Food buffers pH, removes inhibition of gastrin
What are G cells stimulated by?
Peptides and AA in stomach lumen
Vagus n - GRP and ACh
What happens in the intestinal phase of digestion?
10% HCl
Initially - duodenum stretch enhances gastrin secretion
Lipids in lumen stimulate enterogastric reflex - reduces vagal stimulation, inhibits stomach secretion.
Chyme - CCK, secretin and GIP - inhibit stomach secretion.
What are the 4 main proteases?
Trypsin
Chymotryrpsin
Elastase
Carboxypeptidase
Why is it important for chyme release into duodenum to be controlled?
Mass water influx would can cause hypovolaemia.
Stomach impermeable to water.
What is starch made up of?
Straight chain amylose
Branched amylopectin
Which enzymes digest starch?
Amylase - 1,4 bonds
Isomaltase - 1,6 bonds
Alpha-dextrins - amylopectin into smaller chunks
What is sucrose?
glucose and fructose
Which monosaccharides can be absorbed?q
Glucose, galactose, fructose
How is glucose absorbed across the gut lumen?
SGLT1 apical
GLUT 2 basolateral = facilitated diffusion
How is fructose absorbed from the gut?
GLUT 5
Why is a mixture of salt and glucose used for oral rehydration?
Glucose stimulates Na uptake via SGLT1. Water follows Na.
What is the main stomach enzyme?
Pepsin
What is the master regulator of proteases in small intestine?
Trypsin
What is an exopeptidase?
Breaks bonds at the end of polypeptide -> dipeptide or AA
What is an endopeptidase?
Breaks bonds in the middle of polypeptide -> smaller polypeptide.
How are proteins absorbed?
Na+-AA apical transporters
Dipeptides + tripeptides by PT1 (peptide transporter 1), broken down into AA by cytosolic peptidases.
What stimulates water uptake in large intestine?
Aldosterone stimulates Na channels
How is calcium absorbed in the intestine?
Low lumen conc - active transport (facilitated diff)
High lumen conc - paracellular
Why is Vit D important for calcium absorption?
Essential for calbindin synthesis
What macroscopic features might you see in coeliac disease?
Absence of intestinal villi
Crypt lengthening
Mucosal damage
How can hepatitis cause cholestatic jaundice?
Swollen hepatocytes compress low pressure bile canaliculi and sinusoids -> stasis.
What would you see upon investigations with pre-hepatic jaundice?
Dark stools - more stercobilin
Raised serum bilirubin
Raised urine urobilinogen
What would you see on investigation of intra-hepatic jaundice?
Raised serum bilirubin
Conjugated bilirubin in urine - dark
What signs are associated with post-hepatic jaundice?
Pruritis
Pale stools
Dark urine
What investigation results indicate post-hepatic jaundice?
Raised serum bilirubin
Decrease urinary urobilinogen
Conjugated bilirubin in urine
What are the 2 main causes of bile duct obstruction?
Gallstone
Carcinoma of head of pancreas
What markers will be raised in bile duct obstruction?
Alk phos
Gamma GT
What is cholangitis, what is it usually caused by?
Infection in common bile duct.
Complication of obstruction.
E.Coli
What is charcot’s triad?
Fever, RUQ pain, jaundice = cholangitis
What is acute cholecystitis?
Infection within gallbladder - complication of cystic duct obstruction.
NOT colicky pain
What are the 2 causes of pancreatitis?
Gallstones
Alcohol
What is used to diagnose pancreatitis?
Raised amylase and lipase
What are the branches of SMA?
Jejunal Ileal Ileocolic Right colic Middle colic
What are the branches of IMA?
Left colic - anastomoses with middle colic to form marginal.
Sigmoid branches
Rectal branches (once superior rectal a)
What consequence of chronic reflux disease will commonly cause dysphagia?
Fibrous strictures
What type of chronic gastritis can lead to a megaloblastic anaemia?
Chronic autoimmune gastritis - antibodies that attack parietal cells. Pernicious anaemia.
How does the structure of the large intestine differ to the small intestine?
No villi No plicae circulares Shorter Wider Smoother appearance
What are 2 functions of the large intestine?
Vit K synthesis by bacteria
Water reabsorption
How is the longitudinal muscle different in the large intestine?
Incomplete - forms 3 bands called teniae coli
Teniae coli contracting form hausfrau.
Appendices epiploicae - fat appendages.
How is water reabsorbed in the large intestine?
ENaC - induced by aldosterone
Tight junctions prevent water loss
What extra-intestinal problems are associated with IBD?
MSK pain - arthritis
Skin - erythema nodosum, psoriasis
Eye problems
Primary sclerosing cholangitis
Which IBD is smoking associated with?
Crohns
What are some causes of IBD?
Genetic Gut organisms Antibiotics Infections Diet
What is ‘lead pipe colon’?
Loss of haustra
Suggests UC
Crohn’s pain is most likely to present in which abdominal region?
RLQ - ileum
What gross pathology is associated with crohn’s?
Hyperaemia - red, inflamed Mucosal oedema - cobblestone Scar tissue - thickened wall, narrowed lumen Fistulae Transmural inflammation
Name a microscopic feature of Crohn’s?
Granuloma
What might you find in blood results from patients with IBD?
Anaemia
What gross pathology is visible in UC?
Crypt abscesses and distortion
Pseudopolyps
Loss of haustra
What is the underlying cause of UC?
Inflammatory infiltrate within lamina propria.
Superficial mucosal inflammation.
UC or Crohns: LI only.
UC - no malnutrition.
How do the patterns of UC and Crohn’s differ?
Crohns - discontinuous skip lesions
US - continuous
Name 4 types of perianal disease associated with Crohns.
Fistula
Perianal fissure
Haemorrhoids
Skin tag
Fibrosis and narrowing occurs in Crohns or UC?
Crohns - scar tissue formation
What are 3 causes of bleeding into the gut?
Oesophageal varices
Peptic ulcer
Diverticular disease
What signs might you see if there is bleeding into the gut?
Malaena
Haematemesis
How can urea levels indicate the location of a GI bleed?
If upper GI bleed, protein meal to small intestine leads to increased urea levels while creatinine will remain normal.\
Name 2 causes of retroperitoneal bleeding.
Ruptured AAA
Retroperitoneal veins - if on anti-coagulants
Name 2 causes of bleeding into the peritoneum?
Ectopic pregnancy
Perforated viscus - peptic ulcer or diverticular disease
How does a perforated peptic ulcer differ in severity to perforated diverticular disease?
Peptic ulcer - gastric contents cause chemical peritonitis
Diveritular - bacteria and faeces cause peritoneal sepsis.
What is the danger of bowel obstruction.
Hypovolaemia and dehydration- accumulation of fluid, decreased reabsorption.
Why might acute pancreatitis cause dehydration?
Accumulation of fluid in retroperitoneum
What are red flags for GI cancer?
Anaemia Loss of weight Anorexia Recent onset progressive symptoms Malaena + malaise
Name some differentials for epigastric pain.
Peptic ulcer
Oesophagitis
Pancreatitis
Gastric adenocarcinoma
Where is gastric adenocarcinoma usually found?
Cardia or antrum
RF for gastric cancer?
Smoking
High salt diet
FH
What are 3 types of gastric cancer.
- Adenocarcinoma
- Gastric lymphoma - H.pylori treatment regresses
- GI stromal tumours
Which malignancies commonly spread to liver?
colon, gastric, oesophageal, breast, prostate
What is courvoisier’s law?
Jaundice with enlarged, palpable, non-tender cause is not gallstones.
What is tenesmus and what is it a sign for?
Feeling of incomplete emptying
Rectal cancer
What are 2 common causes of anal bleeding?
Haemorrhoids
Anal fissures
RF for colon adenocarcinoma?
Family History
IBD
Polyposis syndrome - FAP
Diet
What is the adeno-carcinoma sequence?
Benign polyp - polyp grows - dysplasia - adenocarcinoma in situ - invasive adenocarcinoma
Which sided colon cancers usually present first, why ?
Left - smaller lumen with more solid contents leads to obstruction.
Ride side more distensible so obstructive presentation less likely.
Which marker is used for bowel cancers?
CEA
What are 5 types of small bowel cancer?
Adenocarcinoma Stromal Lymphoma Sarcoma Carcinoid
How can you identify GI bacterial infections?
Stool culture
MacConkey agar for salmonella
How does shigella invade large intestine cells?
Plasmid encoded virulence genes - lead to endocytosis
MUCOSA only - no bacteraemia as rarely goes deep.
Which GI infection causes ‘currant jelly’ stools?
Shigella - mucous and blood
How does shigella cause diarrhoea?
- Enters LI and rectal cells by endocytosis.
- Escapes endocytic vesicles and invades cell
- Invades neighbouring cells
- Mucosal abscess as cells die
What is a bacterial cause of gastroenteritis?
Salmonella
What is the pathogenesis of salmonella?
Invade epithelial cells of small intestine
What is a viral cause of gastroenteritis?
Norovirus - winter vomiting bug
What does campylobacter look like on gram stain?
Gram negative - pink, seagull appearance
What is the most common source of campylobacter infections?
Uncooked poultry
What are complications of campylobacter infection?
Early - cholecystitis, rash, peritonitis
Late - gullain-barre syndrome, reactive arthritis
What surface landmark can be used to locate the deep ring?
Midpoint inguinal ligament - half way ASIS to pubic tubercle.
What is the most common cause of bowel obstruction?
Hernia
Where does the hepatitc portal vein originate from?
Behind the neck of pancreas - confluence of splenic and superior mesenteric veins.
Which type of hernia affects young infants and usually spontaneously resolves in the first few years?
Umbilical
Where does the linea alba attach from and to?
Xiphoid process to public symphysis
Which structure divides the greater sac into supracolic and infracolic compartments?
Transverse mesocolon
Which structure lies around the oesophageal hiatus to help prevent reflux?
Right crus of diaphragm
What structure passes through the central tendon of the diaphragm?
IVC
What type of hernia might be precipitated by a weakened conjoint tendon?
Direct Inguinal Hernia
Conjoint tendon reinforces medial part of posterior wall, behind superficial inguinal ring.
What is the difference between a strangulated and an incarcerated hernia?
Strangulated - compromised blood supply
Incarcerated - irreducible/stuck
What forms the anterior boundary of the lesser sac?
Posterior stomach
Lesser omentum
What forms the posterior boundary of the lesser sac?
Diaphragm
Pancreas
What provides the liver with the greatest structural support within the abdominal cavity?
IVC
How does H.pylori cause chronic gastritis?
Degrades mucus layer
Releases cytotoxins
In pancreatic secretions, what happens to the concentration of HCO3- if flow rates increase?
More HCO3- as flow increases
