GASTROINTESTINAL SYSTEM
1. ANATOMY OF THE GASTROINTESTINAL SYSTEM
1.1 General Features of the GI System
✔ Derived from endoderm (mucosa) and mesoderm (muscle, serosa, blood supply).
✔ Major Functions:
- Digestion → Breakdown of food into absorbable molecules.
- Absorption → Uptake of nutrients into the bloodstream.
- Secretion → Enzymes, mucus, and hormones for digestion and motility.
- Excretion → Removal of waste products via feces.
- Immune Function → Gut-associated lymphoid tissue (GALT).
1.2 Divisions of the GI System
✔ Divided into Upper and Lower GI Tract based on anatomical and functional roles.
1.2.1 Upper GI Tract
✔ Mouth (Oral Cavity) → Mastication, saliva production, taste perception.
✔ Pharynx → Common pathway for food and air, contains tonsils for immune defense.
✔ Esophagus → Muscular tube with upper and lower esophageal sphincters (UES, LES).
✔ Stomach → Acidic environment for protein digestion, churns food into chyme.
1.2.2 Lower GI Tract
✔ Small Intestine → Primary site for digestion and absorption.
✔ Large Intestine (Colon) → Water absorption, stool formation, gut microbiota.
✔ Rectum & Anus → Waste elimination, controlled by internal and external anal sphincters.
1.3 Layers of the GI Tract (From Inner to Outer)
✔ Mucosa → Epithelium, lamina propria (GALT), muscularis mucosa.
✔ Submucosa → Dense connective tissue, Meissner’s plexus (secretion control).
✔ Muscularis Externa → Inner circular and outer longitudinal muscles, Auerbach’s plexus (motility).
✔ Serosa (Adventitia in Some Areas) → Outermost protective layer, peritoneal covering.
1.4 Accessory Organs of Digestion
✔ Salivary Glands → Parotid, submandibular, sublingual (produce enzymes like amylase).
✔ Liver → Bile production, detoxification, glycogen storage, protein synthesis.
✔ Gallbladder → Stores bile, releases it via common bile duct.
✔ Pancreas → Exocrine (enzymes like lipase, amylase) & endocrine (insulin, glucagon) functions.
2. PHYSIOLOGY OF THE GASTROINTESTINAL SYSTEM
2.1 Regulation of GI Motility
✔ Controlled by Enteric Nervous System (ENS) and Autonomic Nervous System (ANS).
✔ Myenteric (Auerbach’s) Plexus → Controls peristalsis & motility.
✔ Submucosal (Meissner’s) Plexus → Regulates secretion & blood flow.
✔ Key Movements:
- Peristalsis → Propels food forward.
- Segmentation → Mixing movements for digestion.
- Mass Movements → Large bowel contractions before defecation.
2.2 Digestion & Absorption
✔ Carbohydrates → Digested by amylase, absorbed as monosaccharides.
✔ Proteins → Pepsin & pancreatic proteases break them into amino acids.
✔ Fats → Emulsified by bile, digested by lipases into fatty acids.
✔ Vitamins & Minerals:
- Vitamin B12 → Absorbed in the ileum via intrinsic factor.
- Iron → Absorbed in the duodenum.
2.3 Hormonal Regulation of Digestion
✔ Gastrin → Stimulates acid secretion in the stomach.
✔ Cholecystokinin (CCK) → Stimulates gallbladder contraction & pancreatic secretion.
✔ Secretin → Stimulates bicarbonate secretion from pancreas.
✔ Ghrelin → Increases appetite.
✔ Leptin → Decreases appetite.
3. PATHOLOGY OF THE GASTROINTESTINAL SYSTEM
3.1 Esophageal Disorders
✔ Gastroesophageal Reflux Disease (GERD) → Acid reflux due to LES dysfunction.
✔ Achalasia → Failure of LES relaxation, "bird’s beak" sign on barium swallow.
✔ Esophageal Cancer → Squamous cell carcinoma (upper) vs. Adenocarcinoma (lower).
3.2 Stomach Disorders
✔ Gastritis → Inflammation due to H. pylori or NSAIDs.
✔ Peptic Ulcer Disease (PUD) → Duodenal (pain relieved by food) vs. Gastric ulcers.
✔ Gastric Cancer → Associated with H. pylori, smoking, nitrates.
3.3 Intestinal Disorders
✔ Malabsorption Syndromes:
- Celiac Disease → Gluten intolerance, villous atrophy.
- Lactose Intolerance → Deficiency of lactase enzyme.
✔ Inflammatory Bowel Disease (IBD): - Crohn’s Disease → Skip lesions, transmural inflammation, granulomas.
- Ulcerative Colitis → Continuous lesions, mucosal inflammation, crypt abscesses.
✔ Colorectal Cancer → Right-sided (bleeding), left-sided (obstruction).
3.4 Hepatobiliary & Pancreatic Disorders
✔ Hepatitis → Viral (A, B, C, D, E), autoimmune, alcoholic.
✔ Cirrhosis → Liver fibrosis, portal hypertension, ascites.
✔ Cholelithiasis (Gallstones) → Cholesterol (most common) vs. Pigment stones.
✔ Pancreatitis → Acute (enzymatic autodigestion) vs. Chronic (irreversible damage).
4. CLINICAL EXAMINATION OF THE GASTROINTESTINAL SYSTEM
4.1 History Taking
✔ Dysphagia → Difficulty swallowing (oropharyngeal vs. esophageal).
✔ Abdominal Pain → Localized vs. generalized (visceral or somatic).
✔ Altered Bowel Habits → Diarrhea, constipation, steatorrhea.
✔ GI Bleeding → Hematemesis (upper GI), melena (black stool), hematochezia (fresh blood in stool).
4.2 Physical Examination
✔ Inspection → Jaundice, distension, scars, striae, caput medusae.
✔ Palpation → Organomegaly (liver, spleen), tenderness (McBurney’s point for appendicitis).
✔ Percussion → Shifting dullness (ascites), liver span measurement.
✔ Auscultation → Bowel sounds (hyperactive in obstruction, absent in ileus).
4.3 Special Tests
✔ Murphy’s Sign → Positive in acute cholecystitis.
✔ Rovsing’s Sign → Positive in appendicitis.
✔ Psoas Sign → Indicates retrocecal appendicitis.
✔ Courvoisier’s Sign → Painless jaundice + enlarged gallbladder (pancreatic cancer).
5. HIGH-YIELD PG EXAM PEARLS
✔ GERD Treatment → PPI > H2 blockers > Lifestyle changes.
✔ Crohn’s vs. UC → Cobblestone (Crohn’s) vs. Lead-pipe (UC) appearance.
✔ Acute Pancreatitis Causes → Gallstones, Alcohol (most common).
✔ Cirrhosis Marker → AST > ALT (alcoholic liver disease).
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