This document summarizes gastrointestinal secretions from several organs. The pancreas secretes enzymes like lipase, amylase and proteases to digest fat, carbohydrates and proteins. The gallbladder stores and concentrates bile produced by the liver which contains bile salts that emulsify fats to aid digestion. The small intestine produces mucus, enzymes to further break down nutrients, and bicarbonate to neutralize acid. The large intestine secretes mucus and bicarbonate to protect its walls. Hormones like CCK and secretin regulate secretions from the pancreas and bile ducts.

1. Gastrointestinal physiology GIT Secretions (Cont). Dr.M.A.M.Shaikhani.

7. Bile secretion: It helps : fat digestion by saponification & emulsification of fats. Essential for excretion of several important waste products from blood as billirubin & cholesterol. The amount is 1000ml./day.Composition of bile:about 50% are bile salts + billirubin,cholesterol,lecithin & plasma electrolytes. In the gall bladder water & large amounts of electrolytes except Ca++ are reabsorbed by gall bladder mucosa, but the other constituents bile salts,cholesterol & lecithin are not reabsorbed so become highly concentrated .

8. The Gallbladder Figure 24.21a, b

9. Figure 24.21a, b Bile Salts and Emulsification fat globule Water (polar) bile salts fat droplets bile salt phospholipids triglycerides Increases surface area for attack by lipases. polar coating

13. Gall bladder Cholesterol Large intestine Ileum Duodenum Liver Bile salts Stomach Bile salts Bile salts Bile salts Bile salts Bile salts Sphincter of Oddi Portal circulation These salts are reabsorbed in the ileum and returned to the liver where they are once again secreted into bile  only 3-4 g of bile salts in body, thus highly recycled = active transport