PY4.1-12 | Gastro-intestinal Physiology — Glossary

The continuous muscular tube (~7.6 m) from mouth to anus through which food passes for digestion and absorption.

Propulsive wave of contraction preceded by relaxation that moves contents along the GIT, mediated by Auerbach's plexus.

Mixing contractions of the small intestine that churn contents without net forward propulsion, enhancing digestion and absorption.

A network of 500 million neurons in the gut wall that can function autonomously; often called the 'second brain'.

Submucosal nerve plexus in the gut wall that controls glandular secretion and mucosal blood flow.

Myenteric nerve plexus between the longitudinal and circular muscle layers that controls GIT motility.

GI hormone secreted by G cells of the gastric antrum that stimulates HCl and pepsinogen secretion.

GI hormone from duodenal I cells that causes gallbladder contraction, pancreatic enzyme secretion, and delays gastric emptying.

GI hormone from duodenal S cells triggered by acid; stimulates bicarbonate-rich pancreatic secretion and inhibits gastric acid.

Enzyme in saliva that begins starch digestion by breaking it into maltose; inactivated by gastric acid.

Inactive zymogen secreted by chief cells; activated to pepsin by HCl at pH < 2 to digest proteins.

Glycoprotein secreted by parietal cells essential for vitamin B12 absorption in the terminal ileum; deficiency causes pernicious anaemia.

The enzyme on parietal cell apical membrane that secretes H+ in exchange for K+; target of PPI drugs.

Brush border enzyme that activates trypsinogen to trypsin, initiating the cascade of pancreatic enzyme activation.

Amphipathic molecules synthesised from cholesterol in the liver that emulsify dietary fats into micelles for lipase action.

Recycling of bile salts: secreted into duodenum, reabsorbed in terminal ileum (95%), returned to liver via portal vein; cycles 6-8 times daily.

Small aggregates of bile salts surrounding digested fat products that deliver them to the brush border for absorption.

Lipoprotein particles assembled in enterocytes that transport absorbed dietary lipids via lacteals and lymphatic system into blood.

Sodium-glucose co-transporter on the apical membrane of enterocytes that absorbs glucose and galactose by secondary active transport.

Cyclical pattern of GIT contractions during fasting (every 90 minutes, mediated by motilin) that sweeps residual contents and bacteria distally.

Condition caused by incompetent lower oesophageal sphincter allowing acid reflux; can progress to Barrett's oesophagus.

Coordination centre in the dorsal vagal complex of the medulla that integrates inputs from CTZ, vagal afferents, and vestibular system to trigger emesis.

Coordinated reflex triggered by rectal distension: intrinsic (myenteric) and parasympathetic (S2-S4) reflexes relax the internal sphincter; voluntary relaxation of external sphincter completes the act.

Brush border disaccharidase that splits lactose into glucose and galactose; deficiency causes lactose intolerance.

Functional unit of the liver: hexagonal structure with a central vein, portal triads at corners, and hepatocyte plates between sinusoids.