Introduction to GI: Peptic Ulcer Case

Introduction to GI: Peptic Ulcer Case

GI Functions

The GI system performs four interdependent functions: motility (propulsion and mixing of contents), secretion (enzymes, acid, bile, mucus), digestion (chemical breakdown of food), and absorption (transfer of nutrients to blood/lymph). Disruption of any one function typically impairs the others — the peptic ulcer case illustrates this clearly.

Clinical Case: Paralytic Ileus

A patient post-abdominal surgery develops paralytic ileus (loss of propulsive motility). Because motility is absent, secretions accumulate in the bowel lumen without being absorbed. This leads to progressive hypovolaemia (fluid sequestered in gut), demonstrated by BP 105/55 mmHg and tachycardia.

GI Wall Structure

The GI wall has four layers (from lumen outward): mucosa (epithelium + lamina propria + muscularis mucosae), submucosa (loose CT, submucosal/Meissner's plexus), muscularis externa (circular layer + longitudinal layer; myenteric/Auerbach's plexus between them), and serosa (visceral peritoneum) or adventitia.

Enteric nervous system (ENS): the intrinsic nervous system of the gut. Submucosal plexus (Meissner's): regulates secretion and local blood flow. Myenteric plexus (Auerbach's): regulates motility. The ENS can function independently of the CNS — it is sometimes called the "second brain."

GI Signalling

GI hormones are secreted into the bloodstream (endocrine): gastrin (G cells, pyloric glands → stimulates HCl), cholecystokinin/CCK (I cells, duodenum/jejunum → stimulates enzyme secretion + gall bladder contraction), secretin (S cells, duodenum → stimulates HCO3⁻ secretion), GIP (K cells → inhibits gastric acid + stimulates insulin). Paracrine signalling (local): histamine (ECL cells → stimulates parietal cells), somatostatin (D cells → inhibits acid + gastrin).

Gastric Glands

The gastric body/fundus contains oxyntic (acid-secreting) glands: parietal cells (secrete HCl and intrinsic factor), chief cells (secrete pepsinogen and gastric lipase), mucous neck cells (secrete mucus), enterochromaffin-like (ECL) cells (secrete histamine in response to gastrin). Pyloric glands (antrum): G cells (secrete gastrin) and mucus cells. Pepsinogen is activated to pepsin by the low pH (HCl).