CHO metabolism

Question 1

What are the 2 stages of CHO metabolism?

Answer 1

Luminal stage and membranous phase

Question 2

Describe what happens in the luminal phase

Answer 2

1. Amylase breaks down starch and glycogen into compounds containing 2-9 glucose units
2. a1-4 bonds are hydrolysed
3. Pancreatic juice contains a lot of amylase, starch degradation occurs rapidly in the SI
4. Products are maltose, glucose, isomaltose, a-limit dextrans, maltotriose

Question 3

Describe what happens during the membranous phase?

Answer 3

1. Membrane bound enzymes break down simple CHO to monosaccharides
2. Absorption of glucose and galactose linked to Na absorption
3. Na-K-ATPase pumps Na out of epithelial cells and into ECF, setting up an electrochemical gradient
4. Dietary Na diffuses down conc. gradient from lumen into cell releasing E for monosaccharide to be absorbed
5. Na and CHO bind to cotransporter protein and move into cells
6. Transport continues until all glucose/galactose is absorbed
7. Digestive juice contains a high Na conc. so even if dietary Na is low, absorption will still continue
8. Monosaccharides accumulate in epithelial cells, CHO move into blood via facilitated diffusion
9. Transported in portal vein to liver where stored as glycogen or released into general circulation as glucose