fat metabolism II

are lipids hydrophobic or hydrophillic?

hydrophobic

are digestive enzymes hydrophobic or hydrophillic?

hydrophilic

what kind of environment do digestive enzymes operate in?

aqueous

where does fat digestion indirectly start in?

the mouth

what gland releases lingual lipase?

serous gland

where does fat actually start to get broken in?

the stomach

what is lingual lipase activated by?

stomach acid

lingual lipase is responsible for how much digestion in the stomach?

10-30% of fat digestion

how many fatty acids does lingual lipase cleave?

one fatty acid resulting in a diglyceride

where does gastric lipase come from?

secreted by chief cells in the gastric mucosa

how many fatty acids does gastric lipase cleave?

one fatty acid resulting in a diglyceride

what kind of chain fatty acids do lingual and gastric lipase act on?

short and medium chain fatty acids

do lingual lipase and gastric lipase requie bile to emulsify fat?

no, but they must be emulsified to some extent in the stomach

what mechanism mechanically emulsifies contents?

stomach contractions

how does undigested fat affect gastric emptying?

delays it

what needs to occur to digest long chain fatty acids?

• lower acidity

• more specialized lipases

• more emulsification

what is acidity neutralized by?

bicarbonate secreted by the pancreas

where is pancreatic lipase released from?

pancreas

what home stimulates the gall bladder to release bile salts?

cholecystokini (CCK)

what does emulsification result in?

droplets of fat with hydrophobic ends facing inward and an increased surface are the outside for digestion (micelles)

what does pancreatic lipase break TG into?

• diglycerides, monoglycerides, free fatty acids, and glycerol

• glycerol and free fatty acids contribute to emulsification by precipitating with calcium to form a calcium “soap”

what are the end products of lipase digestion?

• free fatty acids and monoglycerides

• short chain fatty acids and medium chain fatty acids can diffuse across the brush border

what forms are fat absorbed in?

free fatty acids and monoglycerides

what is required for the activation of pancreatic lipase?

• protein colipase

• calcium ions

• bile salts

what does colipase do?

acts as an anchor that allows lipase to attach to the molecule and cleave fatty acids

what is pancreatic lipase activated by?

trypsin

where are phospholipids digested?

the small intestine

what are phospholipid hydrolyzed by?

a specific esterase, phospholipase a2

what are the characteristics of phospholipase a2?

• secreted by the pancreas

• is activated in the intestine by trypsin

• breaks down dietary phospholipids and phosphatidylcholine released from the bile

what are the end products of phospholipid digestion?

1 free fatty acid and lysophospholipid (lysolecithin)

what are incorporated into micelles?

free fatty acids and lysophospholipid

what is cholesterol in food combined with?

fatty acids

can cholesterol esters be absorbed?

no, they are hydrolyzed into free cholesterol and fatty acids

where is cholesterol esterase secreted?

pancreas

does cholesterol need to be digested?

no and once free incorporated into micelles

what affect do phytosterols have on micelles?

they can displace cholesterol from micelles and decrease its absorption

digestion of fats primarily occurs where?

small intestin

what is released when fat enters the small intestine?

bile from the gallbladder

what emulsifies fat?

bile

how does bile emulsify fats?

it breaks down large fat globules into smaller droplets, increasing the surface area for enzymes to act upon

what acts on the fats after bile?

pancreatic lipase breaks them down into monoglycerides and fatty acids

what do monoglycerides and fatty acids combine with?

they combine with bile salts to form micelles

what do micelles do?

they help transport fat breakdown products to the surface of the intestinal cell for absorption

what are the fat breakdown products?

• monoglycerides

• fatty acids

• fat-soluble vitamins