absorption of carbs, proteins and lipids

Question 1

describe how water is absorbed

Answer 1

across the internal mucosa. water can move freely back & forth but net osmosis occurs whenever a concentration gradient is established between lumen and interstitial fluid.

Question 2

describe how glucose is absorbed

Answer 2

1. Glucose is co-transported with Na+ ions into the cells on a cotransporter SGLUT1
2. Glucose then exits the cell, to the interstitial fluid down the concentration gradient via GLUT2 into the portal circulation towards the liver.
3. The NA+ that entered with the glucose is actively pumped out into the interstitial fluid by NA+/K+ATPase, which maintains the NA+ gradient

Question 3

describe how fructose and galactose are absorbed

Answer 3

1. Galactose is transported into enterocytes via SGLT1
2. Fructose is transported into enterocytes by facilitated diffusion via GLUT5
3. Galactose and fructose exit enterocytes via GLUT2

Question 4

describe what chylomicrons and how they are formed

Answer 4

A chylomicron is a large lipoprotein that enters the lymphatic system before being released into the blood stream which transports them to the liver.

1. When short & medium fatty acid chains enter the enterocyte, they can be directly absorbed into the blood via capillary.
2. Long chain fatty acids are re-associated with the glycerol backbone & triglycerides are formed again.
3. Within the enterocyte triglycerides are joined by: protein carrier, cholesterol esters and phospholipids to form chylomicrons.

Question 5

describe lipid absorption

Answer 5

Bile salts emulsify lipids and pancreatic lipases breaks them down to free fatty acids and monoglycerides which are transported into enterocytes

Question 6

what is the difference between LDL and HDL

Answer 6

LDL: carry cholesterol and other lipids from the liver to tissues in the body

HDL: responsible for carrying cholesterol out of the bloodstream into the liver.

Question 7

how are proteins absorbed

Answer 7

Amino acids are transported into the epithelial cells by secondary active transport coupled with NA+ transport. Move into capillary bed my facilitated diffusion.