PY4.1-12 | Gastro-intestinal Physiology — Summary & Reflection

KEY TAKEAWAYS

Key Takeaways — Gastro-intestinal Physiology (PY4.1–PY4.12)

• Functional anatomy: Alimentary canal = 7.6m tube; 4-layer wall; ENS = "second brain" (500M neurons in Meissner's + Auerbach's plexuses).

• GI hormones: Gastrin (acid), Secretin (HCO₃⁻), CCK (enzymes + bile), GIP (anti-acid + insulin), Motilin (MMC), Ghrelin (hunger), Somatostatin (universal inhibitor).

• Secretions: All four secretions (saliva, gastric, pancreatic, intestinal) follow a pattern: composition → mechanism → functions → regulation. Master this pattern for any secretion you're asked about.

• Digestion & absorption: Carbohydrates → SGLT-1/GLUT-5 → portal blood; Fats → micelles → chylomicrons → lacteals/lymph; Proteins → amino acids → portal blood. B12 needs intrinsic factor → terminal ileum.

• Movements: Peristalsis (propulsion), segmentation (mixing), mass peristalsis (gastrocolic reflex), MMC (fasting housekeeper). Defecation reflex = S2–S4 parasympathetic + voluntary external sphincter.

• Liver: Bile (emulsifier, not enzyme) + >500 metabolic functions. LFTs test synthetic (albumin, PT), hepatocellular (ALT), and cholestatic (ALP) function.

• Gut-Brain Axis: ENS + vagus + microbiome → bidirectional. Explains IBS, stress ulcers, and newer drug targets (GLP-1 agonists, psychobiotics).

• Applied physiology: PUD (H. pylori, NSAIDs), GERD (LOS incompetence), vomiting (CTZ + vomiting centre), diarrhoea (4 types), paralytic ileus (absent peristalsis), Hirschsprung's (no ganglion cells).

• Clinical examination: Inspection → Palpation → Percussion → Auscultation. Liver palpated from right iliac fossa, spleen from right iliac fossa. Ascites = shifting dullness + fluid thrill.

REFLECT

Kolb Reflection Cycle — GI Physiology

Take 10 minutes to reflect on what you studied today:

1. Concrete Experience (CE): Recall a moment from your own life — a meal that made you feel uncomfortably full, an episode of "butterflies" before an exam, or diarrhoea during travel. Describe the experience briefly.

1. Reflective Observation (RO): Based on what you have learned today, which physiological mechanisms explain that experience? (Consider: gut hormones, gut-brain axis, autonomic effects, or motility changes.)

1. Abstract Conceptualisation (AC): Connect this to a clinical scenario. If a patient presents with similar symptoms that are chronic and recurring, which conditions would you consider? What investigations would you order?

1. Active Experimentation (AE): What will you do differently in your next clinical encounter because of what you learned today? (Example: When taking a GI history, I will ask specifically about meal timing and symptom relation.)