Small Intestine Prof K Sivapalan Small Intestinal Motility

Small Intestine Prof. K. Sivapalan.

Small Intestinal Motility • Segmental movement [mixing 7/min in ileum] • Peristalsis [propagation average 1 cm/min]. • Stimulated by stretch of the wall (dietary fibers). – Obstruction causes over distention and violent peristalsis which causes colicky pain. • Facilitated by, – Parasympathetic stimuli – Gastro-enteric reflex. • Inhibited by, – Sympathetic stimuli. • Irritation to mucosa can cause peristaltic rush and diarrhoea. • Injury to peritoneum causes reflex inhibition and paralysis of the intestine- Paralitic ileus. • Migrating Motor Complex 2013 Small Intestine 2

Intestinal Secretions • Brunner’s glands in duodenum secrets thick mucus in response to acid to protect from acid. • Crypts of Liebercühn – water and electrolytes similar to ECF, 2000 ml/day [? Much more] – Enzyme enterokinase. – Cell division and migration to top of villilife span of the epithelial cell is 5 days • Control of crypts of Liebercühn – autonomics- no effect – VIP- vasodilatation, may stimulate. 2013 Small Intestine 3

Intestinal Villi • Surface area: – Intestine [cylinder]– Valvulae c. – Villi- 0. 33 M 2 1. 00 M 2 10. 0 M 2 • Microvilli 200 M 2 • Surface enzymes: – Disaccharidases – Peptidases – Nucleic acidases • Cells at the top face constant aberration and hypoxia 2013 Small Intestine 4

Fat Absorption • Fat is emulsified by bile salts and lipase digests it. • Micelles formed in the presence of bile salts. • Fatty substences diffuse into the mucosal cell. • Chylomicrons formed and released by exocytosis into ECF. • Chylomicrons are taken by the lymph vessels. 2013 Small Intestine 5

Absorption of CHO and Protein. • Na+ pushed into ECF by active transport • Na+ enters cell from lumen. • The channel is a cotransporter of glucose, maltose and amino acids, peptides. • This is secondary active transport - Importance of salt and glucose in rehydration. • Rate of absorption and dietary fibers 2013 Small Intestine 6

Circulation in Villus • Every villus has a central lacteal which transports chylomicrons. • Blood with oxygen goes towards the tip and nutrients away from the tip. • Arrangement of vessels sets up counter current flow preventing transport of oxygen to tip and nutrients out. • The muscle in the villus contracts from time to time and empties it into the circulation. 2013 Small Intestine 7

ILLEO-CAECAL Valve 2013 Small Intestine 8