BIOC192 Lecture 24 - Metabolism: Absorption and Transport of Fats Flashcards
what are 2 examples of molecules associated with fat metabolism?
1) triacylglycerol
2) cholesterol ester
what solubilises fat in the GI tract?
bile acids
where are bile acids synthesised from?
synthesised from cholesterol in the liver
where are bile acids stored?
stored in the gall bladder as bile
where are bile acids secreted?
secreted into the small intestine in response to cholecystokinin
what does it mean that bile acids are powerful detergents?
powerful detergents with hydrophobic and hydrophilic surfaces that form micelles with triacylglcerols to increase the surface area for digestion
what is the source of the hormone gastrin?
produced in the stomach
what is the source of the hormone secretin?
produced in the duodenum
what is the source of the hormone cholecystokinin?
produced in the duodenum
what is the major stimulus for production of the hormone gastrin?
protein-containing food in the stomach, also para-sympathetic nerves to the stomach
what is the major stimulus for production of the hormone secretin?
HCI in the duodenum
what is the major stimulus for production of the hormone cholecystokinin?
fats and amino acids in the duodenum
what are the major actions of the hormone gastrin?
stimulates the secretion of gastric juices
what are the major actions of the hormone secretin?
stimulates the secretion of alkaline bile and pancreatic fluids
what are the major actions of the hormone cholecystokinin?
stimulates release of pancreatic enzymes and stimulate the release of bile from the gal bladder
what is the digestion of lipids?
- lipids are emulsified by bile salts to form micelles
- pancreatic lipase/colipase enzyme system binds to lipid/aqueous interface of micelle and hydrolyses triacylglcerols
- pancreatic lipase hydrolyses fatty acids at position 1 and 3 of glycerol backbone of triacylglycerol
- smaller micelles form containing bile salts, free fatty acids, monoacylglycerol (and cholesterol)
- micelles are absorbed across the intestinal cell membrane
what does fat malabsorption lead to?
leads to excess of fat and fat soluble vitamins in the faeces
what is fat malabsorption caused by?
caused by conditions that interfere with bile or pancreatic lipase secretion
what is a potent inhibitor of pancreatic lipase?
xenical (orlistat)
what are lipoproteins?
they ‘help’ soluble lipids for transport in blood to tissues
what is the function of lipoproteins?
provide a ‘delivery system’ for transporting lipids into and out of cells
what are the 3 functions of apoproteins?
1) structural for assembly (apoB)
2) ligands for cell surface receptors (poE and apoB)
3) enzyme cofactors (apoCII for lipoprotein lipase)
what are the 4 components of the general lipoprotein structure?
1) phospholipids
2) triglycerides
3) esterified cholesterol
4) unesterified cholesterol
what are the 4 main lipoprotein classes?
1) chylomicrons
2) very low density (VLDL)
3) low density (LDL)
4) high density (HDL)
what are the 2 lipid transport pathways?
1) exogenous chylomicron pathway (dietary fat)
2) endogenous VLDL/LDL pathway (endogenously synthesised fat)
what forms chylomicrons?
triacylglycerols and other lipids combine with apoB in the ER to form chylomicrons
where are chylomicrons secreted from and where do they go?
secreted from the intestinal epithelial cells and enter in the bloodstream via the lymphatic system
how can chylomicrons affect plasma?
can give plasma a ‘milky’ appearance after a fat-rich meal
where is lipoprotein lipase found?
an enzyme found on the epithelial surface
what is the function of lipoprotein lipase?
hydrolyses TAG in lipoproteins to glycerol and fatty acids with the highest activities in the heart, skeletal muscle and adipose tissue
what is lipoprotein lipase activated by?
apoCII
what does a mutation or defect in lipoprotein lipase or apoCII cause?
leads to elevated levels of chylomicrons and plasma triglycerol
