Physiology & Pathways
Which neurotransmitter released from enteric neurons stimulates GI motility?
Acetylcholine stimulates smooth muscle contraction and peristalsis.
What condition is suggested by recurrent abdominal pain ≥1 day/week for 3 months with stool changes?
Irritable Bowel Syndrome (Rome IV criteria).
Which stool marker helps differentiate IBS from IBD?
Faecal calprotectin.
Which receptor system do serotonin receptor antagonists block to treat vomiting?
5-HT3 receptors - require the exact receptor.
Which epithelium lines the oral cavity to resist abrasion?
Non-keratinised stratified squamous epithelium.
Why do osmotic laxatives cause bowel movements?
Osmotic agents increase luminal osmotic pressure → water enters bowel → stool expansion → peristalsis.
Why do duodenal ulcers improve after meals?
Food buffers gastric acid → temporarily reduces mucosal irritation in duodenal ulcers.
What enzyme elevation suggests pancreatitis?
Elevated lipase or amylase.
How do TCAs improve pain in IBS?
TCAs enhance descending inhibitory pain pathways → reduce visceral hypersensitivity.
What structural change occurs in Barrett oesophagus?
Metaplasia: squamous epithelium → intestinal-type columnar epithelium.
A patient with chronic diarrhoea undergoes stool testing and is found to have very low levels of faecal elastase.
What organ dysfunction does this test primarily detect?
Pancreatic exocrine insufficiency.
Why does biliary colic radiate to the right shoulder?
Gallbladder irritation stimulates diaphragm → phrenic nerve referral → right shoulder pain.
Why is colonoscopy considered the gold standard for colonic investigation?
Direct visualisation + biopsy + therapeutic capability.
Why can metoclopramide cause extrapyramidal side effects?
Central D2 blockade in basal ganglia → dopaminergic imbalance → Parkinson-like symptoms.
Why does chronic reflux predispose to oesophageal adenocarcinoma?
Chronic acid injury → metaplasia → dysplasia → adenocarcinoma risk.
Explain the mechanism of vomiting triggered by mucosal injury.
Mucosal injury → serotonin release from enterochromaffin cells → 5HT3 activation on vagal afferents → CTZ → vomiting centre.
Why does pancreatic inflammation cause back pain?
Pancreas is retroperitoneal → inflammation refers pain to posterior spinal nerves → back pain.
How does the urea breath test detect H. pylori infection?
H. pylori urease splits labelled urea → labelled CO₂ detected in breath.
How does loperamide reduce diarrhoea?
Peripheral μ-opioid receptor activation → reduced motility → increased water absorption.
Why can gallstones cause pancreatitis?
Stone obstructs ampulla of Vater → pancreatic enzyme outflow blocked → pancreatic inflammation.
A patient presents with post-prandial right upper quadrant pain that radiates to the shoulder after eating fatty meals.
Cholecystokinin (CCK).
List GI alarm features (red flags) and explain why
investigation rather than IBS diagnosis is important.
Alarm features (bleeding, weight loss, age >50, noctural symptoms) suggest structural disease such as malignancy or IBD rather than functional IBS.
A patient presents with chronic watery diarrhoea but normal colonoscopy findings. Stool testing reveals high levels of bile acids entering the colon.
Which pathophysiological defect in intestinal absorption most likely explains this result?
Bile salt malabsorption due to impaired ileal reabsorption of bile acids, leading to excess bile acids in the colon that stimulate secretion and motility → diarrhoea.
What drug class is domperidone and what are the potential dangerous cardaic effects.
selective peripheral dopamine (D2) receptor antagonist.
Arrhythmia, QT prolongation and CYP3A4 interactions → torsades de pointes risk.
Why does Boerhaave syndrome cause severe mediastinal infection?
Full-thickness oesophageal rupture → leakage of gastric contents into mediastinum → mediastinitis and sepsis.