digestion and absorption of lipids

summarise the process of lipid digestion:

• starts in mouth and stomach, but most takes place in duodenum and ileum

• bile salts (not an enzyme!) emulsify lipids

• then lipase hydrolyses ester bonds

describe the digestion of lipids:

• bile salts neutralise stomach acid and emulsify large lipid globules → smaller lipid droplets

• this increases SA for lipase to act on - triglycerides → fatty acids and monoglycerides

• bile salts surround FA chains and monoglycerides to form micelles, making the FA chains more water soluble

describe the process of absorption of triglycerides:

• micelles contain bile salts, fatty acids and triglycerides

• micelles make fatty acids more water soluble and carry fatty acids to epithelial lining of ileum

• micelles are broken down to release fatty acids and monoglycerides

• micelles maintain a higher concentration of fatty acids to the lining of the ileum

• fatty acids and monoglycerides diffuse into the epithelial cells that line the ileum

• triglycerides reform inside the cell’s ER

• triglycerides are packaged in the Golgi w/ cholesterol and proteins to form chylomicrons for transport

• chylomicrons are released from the epithelial cells by exocytosis into lacteals (lymphatic vessels in the villi)

• chylomicrons are transported via lymph vessels in the lymphatic system to the blood

where is lipase produced?

pancreas

where are bile salts produced and stored? how are they secreted into the duodenum and ileum?

• produced in liver, stored in gall bladder

• secreted into duodenum and ileum via bile duct

why can fatty acids diffuse across the epithelial lining?

non charged/non polar

explain the advantages of lipid droplet and micelle formation:

• droplets increase SA for lipase action

• ∴ faster hydrolysis of triglycerides

• micelles carry fatty acids and glycerol to intestinal epithelial cell