Lipid Digestion and Absorption

Learning Objectives and Guiding Questions

Reading assignment: Meisenberg, pp 281-282; 361-362.

1. Describe the role of emulsification in fat digestion. Increase surface area

A. Where is the site of enzymatic activity in fat digestion? Interface between fat droplets and aqueous medium

B. Where in the gut does fat digestion occur? Small intestine

C. How are emulsions stabilized in the gut (prevented from reforming into fat droplets)?

Stabilized by fatty acid released early phases of digestion

2. Describe the specificity of lipase action.

Specific for long chain fatty acids esterified to alpha position of glycerol

A. What are the products of lipase digestion? Monoglycerides and long chain free fatty acids (FFA)

B. What is the lipase effect on medium chain triglycerides? No effect; unhydrolyzed

3. Describe the composition of mixed micelles. Bile acid and phospholipid

A. What property of bile acids and phospholipids allows them to form mixed micelles? Polar and nonpolar ends aggregate

B. How are free fatty acids and monoglycerides absorbed into mucosal cells? Passive diffusion

C. If triglycerides are going to be resynthesized anyway, why are they digested in the first place? Too big; can't get across cell membrane

4. Describe a chylomicron.

85% triglycerides, some cholesterol and cholesterol esters; found in chyle, formed by lymphatic system draining intestine; transport all dietary lipids into circulation

5. Explain the transport of chylomicrons from the mucosal cell to the bloodstream.

By lymphatic drainage

A. What vein does the thoracic duct empty into? Left subclavian

B. What is in a chylomicron besides triglycerides? Cholesterol and cholesterol esters