31. GI Absorption Flashcards
How does secondary active transport work?
Requires a cotransporter protein to carry the substance across the membrane
What is the key to intestinal absorption?
Na+/K+ ATPase on the basolateral membrane
Why is the Na+/K+ ATPase necessary?
To move Na+ against its electrochemical gradient (out of cell)
How are carbohydrates absorbed?
Which types are absorbed?
Through secondary active transport and facilitated diffusion
Only monosaccharides are absorbed
Which carbohydrates are absorbed fasted?
Which are absorbed the slowest?
Galactose
Fructose
Glucose in the middle
What must occur before protein absorption can occur?
They must be converted into oligopeptides, which occurs in the stomach and intestine
How are proteins absorbed into the intestinal epithelia?
How are they transported into the blood?
Secondary active transport of AAs and di/tripeptides across apical surface
Active transport across basolateral membrane into blood
How are lipids absorbed?
Facilitated diffusion
How are lipids transported into lymph?
Form into chylomicrons in the intestinal epithelial cells and are transported into the lymph vessels through the basolateral membrane
How are chylomicrons transported into the blood?
Lose fatty acids by lipoprotein lipase and become a chylomicron remnant
How are fat soluble vitamins absorbed?
By binding to micelles. Require fats
Facilitated diffusion
What vitamins are fat soluble?
Vitamin D
Vitamin E
Vitamin K
Vitamin A
How does vitamin D deficiency affect calcium absorption?
Decreases by more than 75%
How is Ca2+ absorbed when dietary levels are high?
Paracellular, regulated by vitamin D receptor
How is Ca2+ absorbed when dietary levels are low?
Absorption facilitated by vitamin D
Facilitated diffusion, vesicular transport
