GIS23 Absorption along the GI tract

Question 1

Outline the amounts of nutrients absorbed daily in the small intestine.

Answer 1

1. Carbohydrates: hundreds of grams
2. Fat: 100+ grams
3. Amino acid, ions: 50-100 grams each
4. Water: 7-8L

Question 2

List three structural characteristics of the small intestine which aid in absorption.

Answer 2

1. Valves of Kerckring (plicae circulares / circular folds): duodenum & jejunum
2. Villi
3. Microvilli => brush border
4. Long (2-7 M in length)

Question 3

Which transporter maintains the low intracellular concentration of Na+ in enterocytes?

Answer 3

Na+/K+ ATPase on basal surface

3 Na+ out
2 K+ in

Question 4

What forms the molecular basis of oral rehydration therapy?

Answer 4

Cotransport of Na+ and glucose is accompanied by transport of hundreds (260 per glucose molecule) of water molecules into enterocytes
=> ~5L water absorbed daily

Question 5

Which transporter facilitates downhill efflux of glucose from enterocytes?

Answer 5

GLUT2 on basal / serosal surface