Master Gastrointestinal System
for PLAB 1

Core Concepts

The Gastrointestinal (GI) system is responsible for digestion, absorption of nutrients, and elimination of waste. It comprises the alimentary tract (oesophagus, stomach, small intestine, large intestine, rectum, anus) and accessory organs (liver, pancreas, gallbladder). Common pathologies include inflammatory conditions (e.g., IBD, gastritis, hepatitis), infections (e.g., gastroenteritis, H. pylori), mechanical obstructions (e.g., bowel obstruction, gallstones), motility disorders (e.g., GORD, IBS), and malignancy. Understanding the anatomical regions (upper, mid, lower GI) is crucial for localising symptoms and pathology.

Clinical Presentation

• **Abdominal Pain:** Character (colicky, burning), location (epigastric, RUQ, RLQ, periumbilical, LLQ, suprapubic), radiation, aggravating/relieving factors (e.g., food, defecation).
• **Dysphagia:** Difficulty swallowing (solids, liquids, or both); Odynophagia (painful swallowing).
• **Nausea & Vomiting:** Timing, content, associated symptoms; projectile vomiting (e.g., pyloric stenosis, raised ICP).
• **Heartburn & Regurgitation:** Retrosternal burning pain, acid reflux into the mouth.
• **Change in Bowel Habits:** Diarrhoea (acute/chronic, blood/mucus, frequency), Constipation (frequency, straining, incomplete evacuation).
• **Rectal Bleeding:** Haematochezia (fresh red blood), melaena (black, tarry stools).
• **Jaundice:** Yellowing of skin/sclera, dark urine, pale stools, pruritus.
• **Weight Loss:** Unexplained weight loss is an important alarm symptom.
• **Abdominal Distension:** Bloating, ascites, organomegaly.
• **Fever:** Often indicates infection or inflammation (e.g., appendicitis, diverticulitis, cholangitis).

Diagnosis (Gold Standard)

• **Endoscopy:**
  • **OGD (OesophagoGastroDuodenoscopy):** Gold standard for upper GI conditions (e.g., GORD, PUD, Barrett's oesophagus, malignancy).
  • **Colonoscopy:** Gold standard for lower GI conditions (e.g., colorectal cancer, IBD, polyps).
  • **ERCP (Endoscopic Retrograde Cholangiopancreatography):** Diagnostic and therapeutic for biliary/pancreatic duct pathology (e.g., choledocholithiasis, cholangitis).
• **Imaging:**
  • **Abdominal Ultrasound:** First-line for gallstones, liver pathology, acute appendicitis (paediatrics), ascites.
  • **CT Abdomen/Pelvis:** High sensitivity for acute abdomen, diverticulitis, pancreatitis, malignancy staging, bowel obstruction.
  • **MRI:** Useful for complex IBD, pancreatic pathology, liver lesions.
• **Laboratory Tests:**
  • **FBC, U&Es, LFTs, Amylase/Lipase, CRP/ESR, Coagulation screen.**
  • **Stool Tests:** Faecal occult blood (FOBT/FIT), faecal calprotectin (IBD activity), stool culture (infection).
  • **H. pylori tests:** Urea breath test, stool antigen test (non-invasive), CLO test on biopsy (invasive).

Management (First Line)

• **Lifestyle Modifications:** Diet (e.g., low FODMAP for IBS), smoking cessation, alcohol reduction, weight loss (for GORD).
• **Pharmacological:**
  • **Acid Suppression:** PPIs (e.g., omeprazole) for GORD, PUD; H2RAs (e.g., famotidine).
  • **Motility Agents:** Prokinetics (e.g., metoclopramide) for nausea/vomiting; Laxatives (e.g., Movicol) for constipation; Anti-diarrhoeals (e.g., loperamide).
  • **Anti-inflammatory/Immunosuppressants:** 5-ASA (e.g., mesalazine) for IBD; corticosteroids (acute IBD flare); biologics (e.g., infliximab for severe IBD).
  • **H. pylori Eradication:** Triple therapy (PPI + two antibiotics, e.g., amoxicillin + clarithromycin/metronidazole for 7-14 days).
• **Surgical:** Appendicectomy (acute appendicitis), cholecystectomy (symptomatic gallstones), bowel resection (colorectal cancer, severe IBD, obstruction), hernia repair.
• **Supportive Care:** IV fluids for dehydration, anti-emetics, analgesia.

Exam Red Flags