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Digestion In The Intestine Notes

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Lecture 9 Digestion in the intestine

Secretions in the intestine o Duodenum
 1 litre per day, pH 7.6
 Composition: mucus, water enterokinase, water etc. o Liver
 0.5 litres per day, pH 7.4
 Composition: bile acids, cholesterol, phospholipids etc. o Pancreas
 1~2 litres per day, pH 7.8-8.4 (very alkaline, secretes lots of HCO3-)
 Composition: salts and enzymes (enteropeptidase) Secretions of the pancreas o Endocrine- insulin and glucagon o Exocrine- salts and water, enzymes o Functions of pancreatic juices
 Salts and water (HCO3-, NaCl, Water)= make right environment for enzymes
 Enzymes (proteases, lipases, a-amylases)= digest major classes of foodstuffs o Structure of the pancreas
 Like a bunch of grapes
 Main collecting duct= large stalk; Interlobular duct= small stalk; Acinar=
 Acinar cells fall of zymogen granules for secretory purposes o Movement of newly synthesised proteins through secretory pathway (in Acinar cell)
 Rough ER-->Golgi-->Condensing vacuoles-->Zymogen granules
 5-15g of protein each & every day o Secretion of enzymes
 Key stimulators: CCK & Secretin (lesser role but does give rise to cAMP)
 Cause the release of vesicles by exocytosis
 CCK acts on receptor on basolateral membrane giving rise to IP3 and DAG in cell that leads to exocytosis of materials into lumen (enteric NS acting on M3 receptors has same effect)
 Secretin receptors activated to give rise to cAMP, Somatostatin inhibits this
 Things released into lumen:

• Proteases (Trypsin, chymotrypsin, carboxypeptidases)= as Zymogens

• Lipases & a-amylases= as enzymes o Composition of pancreatic juice made by both Acinar & duct lining epithelial cells
 Acinar cells

• "Leaky" epithelium

• Active/inactive enzymes & Cl1 secreted transcellularly

• Na+ and H20 secreted paracellularly
 Duct-lining epithelial cells

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