Lecture 25: Gastrointestinal 3 - SI & Colon

Question 1

Describe how carbohydrates, proteins, and lipids are digested and absorbed in the SI

Answer 1

Carbohydrates:Broken down by pancreatic amylase, then brush border carbohydrate hydrolases. enter through SGLT1, except for fructose which goes through GLUT 5. goes across basolateral membrane via GLUT2

Proteins: broken down into amino acids, then transporter into cell. pH and pepsin break it down in stomach, trypsin, chymotrypsin, elastase in the SI. brush border peptidases break down oligopeptides to amino acids.

Lipids: emulsified by bile to form micelles, broken down by gastric lipase to diacylglycerides and fatty acids, pancreatic lipase breaks triacylglycerides to free fatty acids. Diffuse across or go by help of MVM-FABP (microvillar membrane fatty acid binding protein) where they are reformed into chylomicrons, go through lymph system lacteal and enter into blood at the subclavian vein.

Question 2

Describe how salt and water are absorbed in the SI and colon

Answer 2

water follows electrolytes via osmosis

Na through NHE, Cl via Cl/HCO3 exchanger

Question 3

Explain how cholera affects the body

Answer 3

cholera clamps adenylyl cyclase on, production of cAMP, acts of CFTR to allow Cl to go out, which pulls out water by osmosis.

Question 4

What does peptide yy do?

Answer 4

slow down rate of gastric emptying and motility, sensor of lipid in the ileum or colon, secreted by mucosal L cells

Question 5

Where does secretion occur in the colon? where do fatty acids get absorbed? what about sodium?

Answer 5

sodium enters via ENaC, fatty acids through SMCT-1 (sodium coupled fatty acid transporter), secretion occurs in the crypts