SN4 SHORT NOTE 5M ★ High-yield

Enumerate the gastrointestinal hormones. Give their sources, stimuli and actions.

Physiology · 1st Professional — Pre-Clinical

Introduction

Gastrointestinal hormones = peptides secreted by endocrine cells scattered through the gut mucosa, which regulate secretion, motility and growth of the digestive tract.

The Four Established Hormones

Hormone	Cell & site	Stimulus	Chief actions
Gastrin	G cell — antrum	Peptides, distension, vagus (GRP)	↑ HCl; ↑ gastric motility; trophic to gastric mucosa
Secretin	S cell — duodenum	Acid, pH < 4.5	↑ Pancreatic bicarbonate; ↓ gastric acid and emptying; ↑ bile
CCK	I cell — duodenum, jejunum	Fatty acids, amino acids	↑ Pancreatic enzymes; contracts gall bladder; relaxes sphincter of Oddi; ↓ gastric emptying; satiety
GIP	K cell — duodenum, jejunum	Glucose, fat, amino acids	↑ Insulin release (incretin); ↓ gastric acid

Secretin was the first hormone ever discovered — Bayliss and Starling, 1902

Other Regulatory Peptides

Peptide	Source	Action
Motilin	M cells, upper small intestine	Initiates the migrating motor complex in fasting
Somatostatin	D cells	Universal inhibitor — suppresses nearly every GI hormone and secretion
VIP	Enteric neurones	Smooth muscle relaxation; ↑ intestinal secretion
GLP-1	L cells, ileum	Incretin — ↑ insulin, ↓ glucagon, ↓ appetite
Ghrelin	Stomach	Hunger hormone — ↑ appetite; rises before meals
Guanylin	Intestinal mucosa	↑ Cl− secretion

The Incretin Effect

Oral glucose → GIP and GLP-1 released from gut → ↑ Insulin secretion → Insulin response is greater after oral than after intravenous glucose

Accounts for 50–70% of the insulin response to a meal
Basis of GLP-1 agonists (liraglutide) and DPP-4 inhibitors (sitagliptin) in type 2 diabetes

Applied Aspects

Zollinger–Ellison syndrome — gastrinoma → very high gastrin → intractable multiple peptic ulcers and diarrhoea
Carcinoid syndrome — serotonin-secreting tumour → flushing, diarrhoea, wheeze; diagnosed by urinary 5-HIAA
VIPoma — watery diarrhoea, hypokalaemia and achlorhydria (WDHA / Verner–Morrison syndrome)
Octreotide, a somatostatin analogue, is used to treat these tumours and variceal bleeding

All questions in Gastrointestinal System

Every Physiology chapter →