Lipid digestion and absorption

Chylomicron

A lipoprotein that transports dietary triglycerides.

What type of fat digestion occurs in the mouth?

Both mechanical (mastication) and chemical

Retinol esterase

Breaks FA from vitamin A. Vitamin A ester --> retinol + FA

pospholipase

Breaks off one FA from phospholipid to get lysophospholipid + FA.

What are the end products of fat digestion?

Fatty acids, glycerol, monoglyceride, lysophospholipid, cholesterol, fat soluble vitamins

Explain chemical fat digestion in the stomach

Gastric lipase breaks down TG-->monoglycerides, diglycerides + short chain and medium chain FA

Explain chemical fat digestion in the mouth

Lingual serous glands release lingual lipase to break ester bonds on triglycerides. TG --> Diglyceride + short chain and medium chain FA

Micelle

Lipid molecules and bile acids come together to form a micelle so the hydrophobic parts of lipids can be on the inside. This allows lipids can get through unstirred water layer.

VLDL

transport fat taken up or made by the liver

LDL

transports cholesterol to body tissues

What happens to mono-glycerides and fatty acids when they are in the cell?

Re-esterified into triglycerides

Lipoprotein lipase

breaks off the 3 fatty acids and glycerol

HDL

cholesterol back to the liver

Cholesterol esterase

separates cholesterol from FA. Cholesterol ester --> cholesterol + FA

What role does CCK play in fat digestion in the small intestine?

stimulates gallbladder to release bile and stimulates pancreas to release lipase and co-lipase.

Chylomicron metabolism

Chylomicrons are exocytosed into general circulation. Fed state: want to store energy. so fat tissues release Lipoprotein Lipase that breaks apart TG to free FA and glycerol. Cell uses FAs and glycerol released into circulation. Unfed state: Haven't eaten in a while, and just ate a meal. The tissue will release LPL. Cell will use FA for fuel (ATP) or stored as TG. Glycerol absorbed in the liver. When chylomicron doesn't have alot of TG left, it is called chylomicron remnant and it is endocytosed into the liver.

Explain fat digestion in the small intestine

Chyme containing large fat droplets enters small intestine and stimulates CCK and secretin. CCK stimulates gallbladder to release bile to emulsify fat. CCK also stimulates pancreas to release lipase and co-lipase. Micelles are broken down by pancreatic lipase with help of co-lipase. Secretin stimulates pancreas to release sodium bicarbonate.

What bonds does hydrolysis break?

Ester

What does mastication do?

Separates hydrophobic (TG, cholesterol esters, free cholesterol, fat soluble vitamins and phospholipids) from hydrophilic foods.

What role does secretin play in fat digestion in the small intestine?

Stimulates pancreas to release sodium bicarbonate

Pancreatic lipase

TG-->MG + FA

How does a chylomicron get into general circulation?

The chylomicron leaves the cell to the lacteal then is in lymphatic circulation. It goes through the thoracic duct to the subclavian vein to the heart, then into general circulation

What do the products of re-esterification form? and where?

They form a chylomicron in the smooth endoplasmic reticulum

Chylomicron remnant

When chylomicron only has 20% or so TG left and is then endocytosed into the liver

Co-lipase

a small protein that unfolds TG so pancreatic lipase can break ester bonds

Chylomicron composition

inside is full of TG, some retinol ester (and other fat soluble vitamins), and cholesterol ester. the outside is hydrophilic with phospholipid layer, some protein and some cholesterol

How are short chain fatty acids and medium chain fatty acids and glycerol are absorbed into the cell?

passive diffusion

What mechanical fat digestion occurs in the stomach?

peristalsis

What happens to LyPl, Vitamin A and cholesterol?

re-esterified into phospholipids, retinol ester, and cholesterol ester