1. Small Intestine Prof. K. Sivapalan.

2. 2013Small Intestine2 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

3. 2013Small Intestine3 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 villi- life span of the epithelial cell is 5 days Control of crypts of Liebercühn - –autonomics- no effect –VIP- vasodilatation, may stimulate.

4. 2013Small Intestine4 Intestinal Villi Surface area: –Intestine [cylinder]-0.33 M 2 –Valvulae c.-1.00 M 2 –Villi-10.0 M 2 Microvilli-200 M 2 Surface enzymes: –Disaccharidases –Peptidases –Nucleic acidases Cells at the top face constant aberration and hypoxia

5. 2013Small Intestine5 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.

6. 2013Small Intestine6 Absorption of CHO and Protein. Na + pushed into ECF by active transport Na + enters cell from lumen. The channel is a co- transporter of glucose, maltose and amino acids, peptides. This is secondary active transport - Importance of salt and glucose in re- hydration. Rate of absorption and dietary fibers

7. 2013Small Intestine7 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.

8. 2013Small Intestine8 ILLEO-CAECAL Valve