Lecture 35

Question 1

Describe the intestinal phase of digestion

Answer 1

regulates gastric emptying (via negative feedback caused by presence of chyme in the small intestine)
secretions: epithelial cells = mucus, digestive (brush border) enzymes
pancreas= HCO3, digestive enzymes
gallbladder=bile
digestion
absorption

Question 2

Describe the cells in the wall of the small intestine

Answer 2

has folds called plica, with projections off of it called villi. Each villi has enterocytes which have microvilli on it, which are where the digestive brush border enzymes are located.
the crypt epithelial cells secrete ions/water/hormones
the goblet cells secrete mucus
capillaries transport nutrients, the lacteal transports fats via the lymphatic system

Question 3

Describe the secretory functions of the pancreas

Answer 3

acinar cells secrete digestive enzymes into the pancreatic duct that goes to the bile duct, controlled by the sphincter of Oddi, duct cells secrete NaHCO3

Question 4

Describe how bile is secreted?

Answer 4

made in the liver, stored in the gall bladder

composed of bile salts, bile pigments, and cholesterol

Question 5

How are carbohydrates digested and absorbed?

Answer 5

amylase in the mouth, nothing in the stomach (low pH inactivates amylase), amylase in the SI, brush border enzymes on epithelial cells (lactase, maltase, sucrase)

glucose/galactose pumped across the apical membrane via the sodium glucose transporter (SGLT) which is driven by the Na/K ATPase. Gets across the basolateral membrane via GLUT2. Fructose passively diffuses across the apical membrane via GLUT5, basolateral membrane via GLUT2

Question 6

How are proteins digested and absorbed?

Answer 6

Digested via pepsin in the stomach, exo/endopeptidases cleave external/internal bonds

1) Di and tripeptides transported via H+ cotransporter, H+ gradient set up by Na/H+ ATPase, Na gradient set up by Na/K ATPase.
2) amino acids enter via cotransport with Na+, leave via exchange with Na+
3) longer chains of proteins are moved through via endo/exocytosis

Question 7

How are fats digested and absorbed?

Answer 7

lipases and colipase (a cofactor) break down TAG to 2 fatty accids, one glycerol+fatty acid (monoglyceride)
go through course emulsion in the stomach (fat droplets suspended within chyme) then bile salts break down the droplet into micelles (fine emulsion) these are then diffused into the cell and reformed as TAGs then sent to the Golgi for processing and packaging into chylomicrons (secretory vesicles) and eventually to the lacteal

Question 8

What is the function of the large intestine? what is the function of the bacteria in the large intestine?

Answer 8

1) absorb water, digest fiber, facilitate bacterial colonization, store waste in the rectum
2) digest fiber, kill pathogens, produce vitamin K