Gastrointestinal disorders Flashcards
List some examples of GIT disorders
- Peptic ulcer disease
- Osmotic and secretory diarrhoea
- Gluten and lactose intolerance
- Inflammatory bowel disorders
- Cirrhosis
- Acute pancreatitis
- Gallstones
What causes mumps?
Viral infection of the salivary glands
What is a possible consequence of mumps particular to males?
Orchitis (testicular inflammation) that may cause infertility in adult males
Name the three types of gastric exocrine cells and the substances they excrete
- Mucous cell
- Parietal cell — HCL, intrinsic factor
- Chief cell — digestive enzymes (most notably pepsinogen; converts to pepsin which breaks down proteins)
Name the three types of stomach endocrine cells and the substances they secrete
- G-cells — release gastrin into blood
- Enterochromaffin-like cells — secrete histamine (paracrine — effects only in the area of the gland secreting it)
- D-cells (found mainly in duodenum but also pyloris) — secrete somatostatin (signals body to stop producing excess acid)
Gastrin is released from G-cells in response to what?
Distension of antrum/vagus nerve stimulation
What is the function of G-cells?
Promotes secretion of HCl and pepsinogen, as well as stomach motility
What inhibits gastrin secretion from G-cells?
Low pH (<4) and the hormone somatostatin
What does omeprazole do?
Shuts down acid production by proton pump inhibitors
What prevents the stomach digesting itself?
A mucous layer trapping HCO3- (local alkaline pH), giving a neutral buffer effect.
List four protective factors of gastroduodenal mucosa
- HCO3- and mucous
- Prostaglandins
- Mucosal blood flow
- Growth factors
List six damaging factors for gastroduodenal mucosa
- H+ and pepsin
- H. pylori
- NSAIDs
- Stress
- Smoking
- Alcohol
Ulcers cannot be present without ____.
Acid
What is the main cause of peptic ulcer disease?
Helicobacter pylori infection
List three contributing factors for peptic ulcer disease
- Stress
- NSAIDs
- Alcohol
True or false: stress, NSAIDs, and alcohol are causal factors for peptic ulcer disease.
How does H. pylori cause peptic ulcer disease?
H. pylori has the enzyme urease which digests urea to produce NH3. It creates a small local area with favourable pH to withstand the harsh environment of the stomach.
Explain why peptic ulcer disease is so common in the duodenum
- H. pylori infects the antrum of the stomach
- This inhibits somatostatin secretion, leading to excess gastrin secretion
- Increased H+ is delivered to the duodenum as acidic food boluses, causing the ulcer
- The duodenum normally responds by secreting HCO3-, but this is inhibited by the H. pylori infection
Name two tests used to dx peptic ulcer disease
Urea breath test and endoscopy
Explain the urea breath test
- The pt ingests urea with a small amount of radioactive carbon
- H. pylori metabolises it to NH3 and radioactive CO2
- The amount of radioactive CO2 exhaled is measured
Describe the rx for peptic ulcer disease
- Omeprazole (proton pump inhibitor)
- Antibiotics for H. pylori
What is Zollinger-Ellison syndrome?
Peptic ulcer disease caused by a tumour (gastrinoma)
Where is the gastrinoma often located?
Head of the pancreas
How does a gastrinoma cause peptic ulcer disease?
The tumour secretes large amounts of gastrin into the blood, inducing excessive H+ secretion by parietal cells
Describe three tests for dx of peptic ulcer disease that is not caused by a tumour
- Serum gastrin levels — tested after fasting on at least three separate occasions (levels should be low)
- Pentagastrin test — infusion of a gastrin homologue while H+ is monitored; normally would increase acid but if a gastrinoma already has levels extremely high there is little change
- Secretin stimulation test — secretin stimulates gastrin secretion from a gastrinoma but not from healthy G-cells, i.e. gastrin increases when a tumour is present
Small intestine absorption is predicated on what factor?
Having a large surface area
Name the three sections of the small intestine
Duodenum, jejunum, and ileum
Pts with celiac disease are intolerant of ____.
Gluten
Celiac is an ____ condition.
Autoimmune
What results from inflammation triggered by gluten ingestion in pts with celiac disease?
Damages villi, decreasing surface area and leading to malabsorption
What is lactose intolerance, and what causes it?
Little/no lactase, a brush border enzyme that digests lactose. It is either genetic or acquired (after diarrhoea/gastroenteritis — may be temporary).
What happens to lactose intolerance pts who ingest lactose or sorbitol?
Osmotic diarrhoea, and metabolism creates methane gas and H2
How is lactose intolerance dx?
- H2 breath test
- Extra solutes in stool (increased faecal osmolar gap)
What is the rx for lactose intolerance?
Lactase tablets, avoid lactose ingestion
Name the four subtypes of diarrhoea
- Osmotic — e.g. lactose intolerance
- Rapid transit — hypermotility, bypass surgery
- Inflammatory — inflammation of intestine
- Secretory — increased secretion of fluid
What causes secretory diarrhoea?
Bacterial; vibrio cholerae causing cholera or enterotoxigenic E. coli
Explain the mechanism of secretory diarrhoea
- Bacterial toxins bind receptors on secretory crypt cells
- Irreversible activation of adenylate cyclase produces excess cAMP
- Causes increased chloride secretion; water follows, causing severe dehydration and hypovolaemia
How is secretory diarrhoea dx?
Identified bacteria in faeces
What is used to rx secretory diarrhoea?
PO or IV rehydration solution (PO preferred — contains glucose which stimulates water uptake in small intestine)
Describe the aetiology of IBD
- Persistent specific infection
- Dysbiosis
- Defective mucosal barrier
- Defective microbial clearance
- Abnormal immunoregulation
Explain dysbiosis
- An altered balance of beneficial vs aggressive bacteria leading to a more pro-inflammatory intestinal flora
- Aggressive bacteria include e. coli, bacteroides, and klebsiella
- Beneficial bacteria include lactobacillis and bifidobacterium species
List four functions of the liver
- Metabolism — gets first pass of intestinal blood
- Detoxification — making urea from nitrogen
- Protein synthesis — albumin (retain fluid in capillaries), clotting factors (∴ bleeding disorders)
- Excreting bile — bilirubin, bile salts (fat absorption)
What is the purpose of the hepatic portal vein?
Not a true vein, it cleans the blood straight after absorption of nutrients in the intestine
What causes jaundice?
Excess bilirubin due to liver dysfunction
What is the source of bilirubin, and how is it excreted?
Produced by metabolism of haemoglobin (metabolism of old RBCs in spleen); extracted from blood by the liver and excreted in bile
What causes neonatal jaundice?
Increased bilirubin ∴ immature liver not keeping up
Increased bilirubin in blood, even in absence of obvious jaundice, can indicate what two things?
Liver disease or blockages such as gallstones
What is hepatic steatosis?
Increased build-up of fat in the liver
What is cirrhosis?
Chronic liver damage leading to scarring and liver failure
Lack of coagulation factors (bleeding) and portal hypertension are indicative of what?
Liver failure
What is ascites?
Fluid in the abdomen (peritoneum)
Name two things that can cause cirrhosis
Liver inflammation and alcohol (not always)
How does cirrhosis develop?
Normal liver cells die by necrosis and are replaces by connective tissue (fibrosis)
What are bile salts?
Bile acids (cholesterol-based) conjugated to amino acids
What is the meaning of ‘amphiphatic’?
Soluble in both fat and water
How are bile salts recycled?
They are taken up by the enterohepatic circulation and transported back to the liver.
Explain the link between ileal resection and bile salts
- Bile salts are not recycled (bile salt malabsorption) and are left in the faeces
- Leads to secretion of Cl- and water in the large intestine; secretory diarrhoea
What is the common term for cholelithiasis?
Gallstones
How is cholelithiasis dx?
Ultrasound
What is the rx for cholelithiasis?
Surgical resection of the gallbladder
What are the functions of the large intestine?
- Absorption of water and some electrolytes
- Synthesis of vitamins by ‘good bacteria’ (vitamin K, essential for coagulation)
- Temporary storage of faeces before excretion
What is diverticulosis?
Diverticula in the large intestine that are easy areas for bacteria to occupy
What is the difference between diverticulosis and diverticulitis?
Diverticulitis involves inflammation
What causes diverticulosis?
Low fibre diet
What is the enteric nervous system?
A division of the autonomic nervous system that governs the GIT
