0
Q
Uptake of primary and secondary bile acids into liver via enterohepatic circulation
A
- reabsorption of about 95% of bile salts
- transported from ileum to liver by portal vein, conjugated to albumin
- liver converts both primary and secondary bile acids to bile salts and secretes them into bile
1
Q
Cholestyramine & bile acid sequestrants
A
- bind bile acids in gut and prevent their reabsorption by ileum
- increased excretion of bile salts in feces & disruption of enterohepatic circulation, forcing the liver to divert more cholesterol to bile acid synthesis
- decrease the amount of cholic acid present in liver, removing inhibition on 7-alpha-hydroxylase and allowing more cholesterol to be converted to bile acids
- these bile acids sequestrants used in rx of hypercholesterolemia
2
Q
Intestinal a.a. absorption
A
Absorption rapid in duodenum & jejunum but slow in ileum
- Dipeptides: transported into enterocytes by H+ co-transport
- Free aa: absorbed across intestinal mucosa by
- Absored aa transported into portal vein and metabolized by liver or enter general circulation
3
Q
Intestinal monosaccharide absorption
A
- does not require insulin
- Transport from lumen to enterocyte:
- Glucose & Galactose: Na+ co-transport (SGLT-1 & SGLT-2)
- Fructose: GLUT5 (facilitated diffusion), independent of sodium
- GLUT2 transport from enterocyte to portal circulation for all monosaccharides
4
Q
Intestinal fat absorption
A
- end products of lipid digestion
- free fatty acids
- 2 monoacyglycerols
- free cholesterol
5
Q
Micelles
A
- bile salts combine with fat digestates to form micelles
- micelles are small spherical cylindrical globules composed of about 20-40 molecules of bile salts
- develop as each bile salt molecule contains a highly fat soluble sterol nucleus and a highly water soluble polar group
- sterol nucleus takes up fatty acids, monoglycerides, and cholesterol, forming a small fat globule in middle of micelle
- once at brush border, the lipids diffuse out of micelles and are taken up by mucosal cells
- bile salts are not absorbed and remain in intestinal lumen
6
Q
Resynthesis of TAG & cholesteryl ester
A
After being absorbed by intestinal mucosal cell, mixture of lipids taken up by sER where resynthesis of TAG and re-esterification of cholesterol takes place. Main enzymes involved in this process are as follow:
- Fatty acyl CoA synthetase (thiokinase): FA -> Fatty Acyl CoA
- TAG Synthase: Monoacylglycerols -> TAG
- Acyltransferases: Lysophospholipids -> Phospholipids
- Acyl CoA: Cholesterol acyltransferase -> Re-esterification of cholesterol
7
Q
Formation of chylomicrons in intestinal mucosal cells
A
- assembled in intestinal mucosal cells
- carry the digested and absorbed lipids to peripheral tissues
- chylomicrons released into lymph and then enter circulation
- rapidly modified to ApoE and ApoC-II in plasma
- ApoC-II is activator for lipoprotein lipase which hydrolyses the TAG w/in the chylomicron to FA and glycerol
8
Q
Absorption of glucose into intestinal mucosal cells
A
Transport from lumen to enterocyte: Glucose & Galactose: Na+ co-transport (SGLT-1 & SGLT-1)
