SMALL INTESTINE PHYSIOLOGY Priyanca Patel

What are the secretions of the exocrine pancreas and small intestine? There are 5 things to remember A pneumonic may help? – Warwick Males Are Horny Dicks… – Water – Mucus – Alkali – Hormones – Digestive enzymes

Mucus -Brunner’s glands in duodenal mucosa -Neutralises duodenal contents -Isotonic solution rich in HCO 3 - Water -Intestinal epithelium secretes Na +, Cl - and HCO 3 - and water follows by osmosis Hormones Some Medic Girls are Very Cliquey -Secretin -Motilin -Gastric Inhibitory Peptide (GIP) -Vasoactive intestinal peptide (VIP) -Cholecystokinin (CCK)

Digestive enzymes: -Trypsin -Chymotrypsin -Carboxypentidase -Pancreatic amylase -Lipases -Other enzymes inc. phospholipase, cholesterol esterases and ribonucleases

Where do the pancreatic secretions originate from? DUCT CELLS: – Secrete alkali – Simulated by secretin and potentiated by CCK and ACh (Vagal tone) ACINAR CELLS – Secrete enzymes into the duodenum – Stimulated by CCK and acetylcholines from parasympathetic, postganglionic neurons of Vagus REST & DIGEST

What is digested in the SI and where? Occurs in the duodenum and small intestine – FATS: Digested by pancreatic lipase  monoglceride and fatty acids – STARCH: completed by pancreatic amylase. Disaccharides  monosacchardies by brush border enzymes – PROTEINS: Broken down to peptide fragments by trypsin and chymotrypsin  amino acids by carboxypeptidase (pancreas) and aminopepsidase (luminal membrane of SI epithelial cells)

Digestion and absorption of fats 1.Emulsification of fats by -Bile salts -Phospholipids

2. Fats digested by pancreatic lipase - Products are held in micelles combined with the bile salts and phospholipids

3. Micelles diffuse into an “unstirred layer” next to the surface of epithelial cells - Fatty acids and monoglycerides then diffuse into the cell membrane - Once inside the cell, fatty acids and monoglycerides are reassembled into fats - Triglyceride droplets are packaged into chylomicrons (with cholesterol and proteins) - Chylomicrons are exported across the basolateral membrane and leave the intestinal vessel via its lymph vessel

How are monosaccharaides transported in the SI? Facilitated diffusion (GLUT5 & GLUT 2) and active transport (SGLT1)

OVERVIEW: Digestion in the SI