Introduction Cholesterol Phospholipid Triglycerides Bile Salts T G

Introduction Cholesterol Phospholipid Triglycerides Bile Salts T G Emulsion Lipase Fatty acids +Monoglycrid+Diglycrid <10 carbone Absorbed > 10 C in Intestine Cells with cholesterol &phspholipid &M. G &D. G& Protein Chylomicrones

Digestion and Absorption of Lipids • 98% of ingested lipids are triacylglycerols (TAGs) • Digestion in the Mouth: enzymes are aqueous -little effect on lipids • Digestion in the Stomach: causes a large physical change: -Churned into droplets: “Chyme”

Gastric Lipase: Begins actual lipid digestion. ~10% of TAGs are hydrolyzed in the stomach. Chyme stimulates cholecystokinin (CCK) to release bile from gallbladder. Bile is an emulsifier

Pancreatic lipase (PL) hydrolyzes insoluble triglyceride by binding to the bile-salt micelles TAGs are partially hydrolyzed: 2 of the 3 F. A. s have ester linkages hydrolyzed and are released. Monoacylglycerol remains = glycerol and 1 fatty acid

Oil droplets will form spherical micelle shapes. Bile salts aid this process clumping fatty acids and monacylglycerols.

Fatty acid micelle: hydrophobic fatty acids & monoacylglycerols are in the interior. Bile salts on exterior. Micelles are small enough to penetrate membrane of intestinal cells. Free fatty acids & monoacylglycerols are reformed into triacylglycerols.

TAGs are combined with membrane & water soluble proteins to form a chylomicron, a lipoprotein. Chylomicrons carry TAGs from intestinal cells into bloodstream via the lymph system.

Lipid transport in the circulation Lipids are insoluble in plasma. In order to be transported they are combined with specific proteins to form lipoproteins: Proteins (apoproteins) Non polar lipids in Cholesterol core (TAG and cholesterol Apoproteins are only weakly associated with a particular ester) lipoprotein and are easily transferred to another lipoprotein of a different class. Apoproteins have various functions including: • Structural role • Binding sites for receptors Activators or co-enzymes for enzymes involved with lipid

Type Ia hyperlipoproteine mia Storage as TG adipose tissue Beta oxidation to

This animation shows how chylomicrons are metabolised once they enter the circulation from the lymphatic system Tissues B 48 E CM CII Taken up by liver (via LDL receptors) E CII HDL B 48 E CMR Lipoprotein lipase CII B 48 E CMR CII Capillary wall (endothelial surface)

Hepatic Lipase

This animation shows how VLDL are metabolised once they enter the circulation from the liver Tissues B 100 VLDL B 100 Some LDL taken up by liver (LDL receptors) E LDL CII Lipoprotein lipase Having lost TAG to tissues LDL contains a large proportion of cholesterol/cholesterol esters Some LDL taken up by other tissues (LDL receptors). LDL delivers cholesterol and TAG to the extra hepatic tissues. Capillary wall (endothelial surface)

VLDL metabolism Tissues B 100 Nascent VLDL Receptor mediated uptake E CII Capillary wall (endothelial surface) CII 75% LDL receptor mediated endocytosis Other tissues E HDL B 100 Remnant VLDL Lipoprotein lipase B 100 LDL CII Remnant VLDL 25% IDL Hepatic lipase E CII E

LDL receptor-mediated endocytosis