Lipid Digestion Flashcards
Triglyceride components
1 Glycerol backbone and 3 fatty acids
Lipid digestion in the mouth
Lingual lipases in the mouth hydrolyze fatty acids less than or equal to 12 carbons.
Lipid digestion in the stomach
Gastric lipases in the stomach hydrolyze fatty acids with less than or equal to 12 carbons.
After exiting the stomach, fat globules enter the small intestine. What do the fat globules interact with here?
Bile salts, which are released from the gall bladder (synthesized in the liver from cholesterol)
Bicarbonate, which is a buffer released from the pancreas.
Pancreatic lipase hydrolyzes triglycerides into monoglycerides and 2 free fatty acids
What occurs when bile salts interact with fat globules in the small intestine?
Bile salts are amphipathic molecules that emulsify fat globules and break them into smaller droplets. This increases the surface area of lipids and makes them more accessible to digestive enzymes.
Eventually, bile salts will surround fat droplets (either droplets of single FA or monoglycerides) to form micelles.
What are micelles
Micelles are a core of lipids surrounded by bile salts. The micelles transport lipids through the intestinal lumen to the epithelial lining of the small intestine and are absorbed into the enterocytes by simple diffusion.
Pancreatic lipase
An enzyme released from the pancreas that hydrolyzes triglycerides into a monoglyceride (glycerol backbone + 1 FA) and 2 free fatty acid
What happens once micelles reach the epithelial lining of the small intestine and are absorbed into the enterocytes by simple diffusion?
Once inside the enterocyte, TAG is reformed and packaged into chylomicrons. Chylomicrons are too large to enter blood capillaries directly, so they must enter the lymph and travel through veins and arteries until they reach blood capillaries.
What are chylomicrons
A core of lipids surrounded by lipoproteins. They transport lipids through the lymph, veins, and arteries until they reach the capillaries.
Once chylomicrons reach capillaries, what happens?
In the capillaries-
- Lipoprotein lipase (LPL) hydrolyzes triglycerides into FA and glycerol.
- Glycerol returns to liver to be reused
- Fatty acids enter cells to be used as energy source or stored as triglycerides in adipose tissue. - Chylomicron remnants are transported to the liver.
Where is VLDL packaged?
Very low density lipoproteins are packaged in the liver. VLDL is composed of lipids (mainly cholesterol).
Two fates of VLDL once it reaches the blood stream
LPL can either digest the VLDL and release the FA to the cells and the glycerol to the liver OR it can be converted into LDL if needed.
LDL
Low density lipoprotein that carries cholesterol to the cells. Too much is bad and can cause plaque buildup, occlusion and stroke/heart attack.
HDL
High density lipoproteins are considered good. They clean up excess cholesterol and take it back to the liver.
