Lipid Digestion and Absorption Flashcards
give 4 dietary lipids
- triacylglycerols (TAGs)
- fat-soluble vitamins (FSVs)
- cholesterol and cholesteryl esters (CEs)
- phospholipids
which dietary lipid is considered “dietary fat” and is a major lipid component of the diet?
triacylglycerols (TAGs)
in what 2 locations does TAG digestion occur?
stomach and small intestine
describe TAG digestion in the stomach
gastric lipase removes one fatty acid (FA) from TAG to create a diacylglycerol (DAG) and a free FA
describe TAG digestion in the small intestine (3)
- SI secretes cholecystokinin (CCK) which acts on gallbladder and pancreas
- gallbladder secretes stored bile into SI, where the bile acids surround the lipid and form small emulsification droplets
- 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
what is the purpose of the emulsification droplets produced by bile in the SI?
allow free lipid to travel through the aqueous digestive tract and to allow for enzymes to work
what are the products of TAG digestion? (2)
- MAGs
2. FAs
what are emulsification droplets also called once digestion is complete?
mixed bile salt micelles
what is the fundtion of mixed bile salt micelles?
transport lipids to brush border for absorption
how does absorption of lipids occur? what does it result in?
occur via transporters along the brush border; results in entry of MAGs and FAs into cells
upon entry into cells, where do the products of lipid digestion go? how do they get there?
to the endoplasmic reticulum via fatty acid binding protein (FABP)
what is reesterification of TAGs?
in the endoplasmic reticulum, MAGs + FAs recombined to yield TAGs
what are the reesterified TAGs packaged into?
chylomicrons, lipid transporters
what do chylomicrons do?
leave the cell and enter the LYMPH
does the liver see fatty acids first? why?
no the rest of the body does because FAs enter the lymph packaged into chylomicrons first, not the bloodstream
describe lipid digestion in nonruminant herbivores, including specifics on horses
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
what is the big difference about lipid digestion in ruminants?
the microbes see the lipids first before lipase in the abomasum
what do microbes do in ruminant lipid digestion? (2)
- in the rumen they break down TAGs into glycerol and FAs
2. biohydrogenation of PUFAs
what happens to the glycerol obtained from the breakdown of TAGs by rumen microbes?
the microbes convert it to VFAs which are then absorbed via the rumen wall
do VFAs travel through the digestive tract of ruminants?
no because the are absorbed directly from the rumen wall
what are fatty acids also called?
PUFAs: polyunsaturated fatty acids
can microbes be around PUFAs?
no, they are toxic to microbes
what do microbes do to PUFAs to make them less toxic?
biohydrogenate the PUFAs into the les toxic, saturated fatty acids (SFAs) by removing double bonds
do saturated fatty acids move through the digestive tract after the rumen?
yes
