Lipid Digestion and Absorption

Question 1

give 4 dietary lipids

Answer 1

1. triacylglycerols (TAGs)
2. fat-soluble vitamins (FSVs)
3. cholesterol and cholesteryl esters (CEs)
4. phospholipids

Question 2

which dietary lipid is considered “dietary fat” and is a major lipid component of the diet?

Answer 2

triacylglycerols (TAGs)

Question 3

in what 2 locations does TAG digestion occur?

Answer 3

stomach and small intestine

Question 4

describe TAG digestion in the stomach

Answer 4

gastric lipase removes one fatty acid (FA) from TAG to create a diacylglycerol (DAG) and a free FA

Question 5

describe TAG digestion in the small intestine (3)

Answer 5

1. SI secretes cholecystokinin (CCK) which acts on gallbladder and pancreas
2. gallbladder secretes stored bile into SI, where the bile acids surround the lipid and form small emulsification droplets
3. pancreas secretes pancreatic lipase and pancreatic colipase, where the colipase allows for lipase to have access to emulsification droplets and the lipase removes one FA from DAG or two FA from TAG to create a monoglycerol (MAG) and free FAs

Question 6

what is the purpose of the emulsification droplets produced by bile in the SI?

Answer 6

allow free lipid to travel through the aqueous digestive tract and to allow for enzymes to work

Question 7

what are the products of TAG digestion? (2)

Answer 7

1. MAGs

2. FAs

Question 8

what are emulsification droplets also called once digestion is complete?

Answer 8

mixed bile salt micelles

Question 9

what is the fundtion of mixed bile salt micelles?

Answer 9

transport lipids to brush border for absorption

Question 10

how does absorption of lipids occur? what does it result in?

Answer 10

occur via transporters along the brush border; results in entry of MAGs and FAs into cells

Question 11

upon entry into cells, where do the products of lipid digestion go? how do they get there?

Answer 11

to the endoplasmic reticulum via fatty acid binding protein (FABP)

Question 12

what is reesterification of TAGs?

Answer 12

in the endoplasmic reticulum, MAGs + FAs recombined to yield TAGs

Question 13

what are the reesterified TAGs packaged into?

Answer 13

chylomicrons, lipid transporters

Question 14

what do chylomicrons do?

Answer 14

leave the cell and enter the LYMPH

Question 15

does the liver see fatty acids first? why?

Answer 15

no the rest of the body does because FAs enter the lymph packaged into chylomicrons first, not the bloodstream

Question 16

describe lipid digestion in nonruminant herbivores, including specifics on horses

Answer 16

same as above listed with stomach and SI
horses have no gallbladder though, so there are just small amounts of bile constantly being secreted into the small intestine

Question 17

what is the big difference about lipid digestion in ruminants?

Answer 17

the microbes see the lipids first before lipase in the abomasum

Question 18

what do microbes do in ruminant lipid digestion? (2)

Answer 18

1. in the rumen they break down TAGs into glycerol and FAs

2. biohydrogenation of PUFAs

Question 19

what happens to the glycerol obtained from the breakdown of TAGs by rumen microbes?

Answer 19

the microbes convert it to VFAs which are then absorbed via the rumen wall

Question 20

do VFAs travel through the digestive tract of ruminants?

Answer 20

no because the are absorbed directly from the rumen wall

Question 21

what are fatty acids also called?

Answer 21

PUFAs: polyunsaturated fatty acids

Question 22

can microbes be around PUFAs?

Answer 22

no, they are toxic to microbes

Question 23

what do microbes do to PUFAs to make them less toxic?

Answer 23

biohydrogenate the PUFAs into the les toxic, saturated fatty acids (SFAs) by removing double bonds

Question 24

do saturated fatty acids move through the digestive tract after the rumen?

Answer 24

yes