BIOC192 Lecture 24 - Metabolism: Absorption and Transport of Fats

Question 1

what are 2 examples of molecules associated with fat metabolism?

Answer 1

1) triacylglycerol

2) cholesterol ester

Question 2

what solubilises fat in the GI tract?

Answer 2

bile acids

Question 3

where are bile acids synthesised from?

Answer 3

synthesised from cholesterol in the liver

Question 4

where are bile acids stored?

Answer 4

stored in the gall bladder as bile

Question 5

where are bile acids secreted?

Answer 5

secreted into the small intestine in response to cholecystokinin

Question 6

what does it mean that bile acids are powerful detergents?

Answer 6

powerful detergents with hydrophobic and hydrophilic surfaces that form micelles with triacylglcerols to increase the surface area for digestion

Question 7

what is the source of the hormone gastrin?

Answer 7

produced in the stomach

Question 8

what is the source of the hormone secretin?

Answer 8

produced in the duodenum

Question 9

what is the source of the hormone cholecystokinin?

Answer 9

produced in the duodenum

Question 10

what is the major stimulus for production of the hormone gastrin?

Answer 10

protein-containing food in the stomach, also para-sympathetic nerves to the stomach

Question 11

what is the major stimulus for production of the hormone secretin?

Answer 11

HCI in the duodenum

Question 12

what is the major stimulus for production of the hormone cholecystokinin?

Answer 12

fats and amino acids in the duodenum

Question 13

what are the major actions of the hormone gastrin?

Answer 13

stimulates the secretion of gastric juices

Question 14

what are the major actions of the hormone secretin?

Answer 14

stimulates the secretion of alkaline bile and pancreatic fluids

Question 15

what are the major actions of the hormone cholecystokinin?

Answer 15

stimulates release of pancreatic enzymes and stimulate the release of bile from the gal bladder

Question 16

what is the digestion of lipids?

Answer 16

• 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

Question 17

what does fat malabsorption lead to?

Answer 17

leads to excess of fat and fat soluble vitamins in the faeces

Question 18

what is fat malabsorption caused by?

Answer 18

caused by conditions that interfere with bile or pancreatic lipase secretion

Question 19

what is a potent inhibitor of pancreatic lipase?

Answer 19

xenical (orlistat)

Question 20

what are lipoproteins?

Answer 20

they ‘help’ soluble lipids for transport in blood to tissues

Question 21

what is the function of lipoproteins?

Answer 21

provide a ‘delivery system’ for transporting lipids into and out of cells

Question 22

what are the 3 functions of apoproteins?

Answer 22

1) structural for assembly (apoB)
2) ligands for cell surface receptors (poE and apoB)
3) enzyme cofactors (apoCII for lipoprotein lipase)

Question 23

what are the 4 components of the general lipoprotein structure?

Answer 23

1) phospholipids
2) triglycerides
3) esterified cholesterol
4) unesterified cholesterol

Question 24

what are the 4 main lipoprotein classes?

Answer 24

1) chylomicrons
2) very low density (VLDL)
3) low density (LDL)
4) high density (HDL)

Question 25

what are the 2 lipid transport pathways?

Answer 25

1) exogenous chylomicron pathway (dietary fat)

2) endogenous VLDL/LDL pathway (endogenously synthesised fat)

Question 26

what forms chylomicrons?

Answer 26

triacylglycerols and other lipids combine with apoB in the ER to form chylomicrons

Question 27

where are chylomicrons secreted from and where do they go?

Answer 27

secreted from the intestinal epithelial cells and enter in the bloodstream via the lymphatic system

Question 28

how can chylomicrons affect plasma?

Answer 28

can give plasma a ‘milky’ appearance after a fat-rich meal

Question 29

where is lipoprotein lipase found?

Answer 29

an enzyme found on the epithelial surface

Question 30

what is the function of lipoprotein lipase?

Answer 30

hydrolyses TAG in lipoproteins to glycerol and fatty acids with the highest activities in the heart, skeletal muscle and adipose tissue

Question 31

what is lipoprotein lipase activated by?

Answer 31

apoCII

Question 32

what does a mutation or defect in lipoprotein lipase or apoCII cause?

Answer 32

leads to elevated levels of chylomicrons and plasma triglycerol