How do we absorb and digest fat

• stomach using lipase which is an enzyme that breaks down the tri glycerides to diglycerides

• Most absorption in SI.

• CCK is released and stimulates the release of bile from the gallbladder and the release of more lipase from the pancreas

• CCK levels can be lower with eating disorders (anorexia)

• Hydrolizes the tris to monos

• Phospholipase – helps to digest phospholipids in duodenum and jejunum (main place where fat is absorbed)

• After absorbed they are reformed into triglycerides and then into lipoproteins

• Lipoproteins are called chylomicrons  these are produced by the small intestine. Enter the blood through the lymphatic system. Once in the blood stream it is broken down into fatty acid and glycerol

• The enzyme in blood vessels breaks down the chylomicrons (lipoprotein lipase)

• TAG  FA + glycerol

• Takes upwards of 2 – 10 hours

Serum  coagulated blood

Plasma  not coagulated blood

VLDL  liver produces the most, liver will surround the lipid with a shell and that is the VLDL

Lipoprotein lipase will break down the TAG  fat + glycerol

The remaining part now is LDL  and this is mainly cholesterol

Most of the LDL is taken up by the cells of the liver. If you eat a diet that tends to be low in saturated fat and cholesterol it will encourage the liver to take up the LDL. If you do the opposite it inhibits the liver’s ability to take up LDL.

Scavenger Pathway for cholesterol uptake  it is designed to reduce the LDL that is in the blood stream. The cells can actually digest the LDL, but what they do after the digestion they tend to deposit it on the wall of blood vessels creating plaque. Tend to deposit the waste on damaged blood vessels. This is why high fat diets are contributing to plaque.

The damage is not sustained on the straight away vessels, but occurs at turns and junctions.

Fruits and vegetables will help decrease the LDL. Along with high anti-oxidant levels.

HDL  has the highest amount of protein (making it the denser than all of the rest)

• Picks up cholesterol from the blood and is carried back to the liver where it is excreted. High HDL levels is GOOD. Low HDL levels are correlated with increased risk of problems.

VLDL  mostly TAG

LDL  Mostly cholesterol

HDL  most protein, not cholesterol

Category: Biochemistry Notes