Fat Absorption, Storage, and Lipolysis Regulation

lingual lipase, gastric lipase

Fat digestion begins in the mouth by — and is continued in the stomach by —

small intestine

In adults, most triacylglycerols, phospholipids, and cholesteryl esters are digested here

bile salts

These are synthesized in the liver, stored in the gallbladder, and are secreted into the duodenum. They emulsify fats.

cholesterol ester lipase or cholesterol esterase

These hydrolyse cholesteryl esters to release fatty acid and free cholesterol

lipase and colipase

After fat is emulsified by bile salts, these 2 pancreatic enzymes digest it.

colipase

Pancreatic lipase is activated by —

fatty acids, 2-monoacylglycerol

Pancreatic lipase hydrolyzes triacylglycerols to give — and —

intestinal epithelial cells

fatty acids and 2-monoacylglycerol are absorbed by —

triacylglycerols, chylomicrons

In the intestinal mucosal cells, — are re-syntheized from fatty acids and 2-monoacylglycerol, then packaged into —

fat

— soluble vitamins are absorbed along with dietary lipids

smooth ER, Golgi

triacylglycerols are reassembled in this organelle, then packaged along with cholesterol, phospholipids, and fat-soluble vitamins into nascent chylomicrons in the —

TAG, apo B-48, cholesterol, phospholipids, and fat-soluble vitamins

Components of nascent chylomicron

lymph, blood

chylomicrons are released into — then into —

mixed micelles

Long chain fatty acids (C12-C20), 2-monoacylglycerol, and bile salts are packaged into —

bile salts, micelles

Short and medium chain FAs (C4-C12) do not require — or — for absorption

ileum

Most bile salts are reabsorbed in the — and recirculated (enterohepatic circulation)

steatorrhea

Condition due to fat malabsorption that results in smelly oily stools

pancreatic lipase, bile salts

Steatorrhea is due to a deficiency of either — or —

fat-soluble vitamins and essential FAs

Steatorrhea inhibits the absorption of — in addition to fat

cystic fibrosis

Steatorrhea is found in patients with —

RNA editing by cytidine deaminase converts a C to a U, producing a stop codon

How Apo-B in the intestine is edited

it is 48% as long of the unedited protein produced in the liver

Apo-B48 is named that because —

microsomal triglyceride transfer protein (MTP); abetalipoproteinemia

Required to transfer lipid to apo-B48, deficiency in it is called —

chylomicrons, chylomicron remnants

Dietary triglycerides are transported from intestine to extra-hepatic tissues by — and dietary cholesterol is transported to the liver by —

VLDL, LDL

Cholesterol and triacylglycerol are transported from liver to extra-hepatic tissues by — and —

HDL

Cholesterol is transported from extrahepatic tissues to liver by —

HDL, mature chylomicrons

Nascent chylomicrons acquire Apo-CII and Apo-E from — in the bloodstream and become —

hydrolyzing triglycerides in circulating chylomicrons and VLDL into free fatty acids and glycerol

Lipoprotein lipase function

adipose

lipoprotein lipase stimulates the synthesis of —

It serves as an activator of LPL, enabling the enzyme to effectively hydrolyze triglycerides

Function of Apo-CII

to deliver dietary TAG to muscle and adipose and cholesterol to liver

Function of chylomicrons

presentation essentially the same

Presentation of familial lipoprotein lipase deficiency vs Apo C-II deficiency

portal blood, liver

Short and medium chain FAs are directly absorbed by the intestinal epithelial cells and transported by — to —

Free glycerol is not used to form TAGs. Glycerol-3-phosphophate is used, and adipocytes lack the enzyme to convert glycerol into glycerol-3-phosphate.

Why glycerol is returned to liver from adipocytes

Olestra

artificial fat substitute designed to allow individuals to obtain the taste and food consistency of fat without the calories from fat

The fatty acids attached to sucrose are resistant to hydrolysis by pancreatic lipase. So, Olestra passes through the intestine intact and is eliminated in the feces.

How Olestra works

inhibits pancreatic lipase activity, decreasing fat absorption (and consequently fat-soluble vitamin absorption)

How weight loss drug Orlistat works

albumin

Transports fatty acids released from adipose tissue into the blood

hormone sensitive lipase

Rate limiting enzyme for lipolysis

increase

Cortisol, thyroid hormone and growth hormone — the expression of hormone sensitive lipase.

inhibits

Insulin — lipolysis

They convert glucose into DHAP then into glycerol 3-phosphate. They cannot convert glycerol into glycerol 3-phosphate because they lack glycerol kinase

What adipocytes use to form TAGs instead of free glycerol

phosphorylating, dephosphorylating

Glucagon regulates key enzymes by — them. Insulin regulates the same enzymes by — them.

ketone bodies

In starved state, brain oxidizes — for energy and uses less glucose