Nutrient Digestion 2 (Fats, Vitamins and Minerals) Flashcards
What form is almost all ingested fat in?
Triacylglycerol
What enzyme is responsible for all fat digestion in the small intestine?
Pancreatic lipase
What are triacylglycerols present as?
Large lipid droplets which are insoluble in water
Why is digestion of fats really slow?
Digestion can only take place at the surface of the droplet because the lipase is water-soluble
What is emulsification?
Dividing of large lipid droplets into smaller droplets
What is the benefit of emulsification?
Increased surface area and increased accessibility to lipase action
What are the 2 main requirements of emulsification?
Mechanical disruption of large lipids into small droplets
Emulsifying agent to prevent small droplets reforming into large droplets
How does mechanical disruption work?
Smooth muscle contraction grinds and mixes lumenal contents
How does emulsifying agent work?
Non-polar portions associate with non-polar interior of lipid droplet leaving polar portions exposed at water surface
Polar portions repel other small lipid droplets prevents them reforming into large droplets
What are emulsifying agents?
Bile salts and phospholipids secreted in bile
Amphiphatic molecules
How is absorption enhanced?
Micelles
What are micelles?
Bile salt + monoglycerides + fatty acids + phospholipids
Similar to emulsion droplets but smaller
What happens when micelles breakdown?
Release of small amounts of free fatty acids and monoglycerides into solution which causes diffusion across plasma membrane of absorbing cells
Dynamic equilibrium between fatty acids and monoglycerides in solution and in micelles - retains most of fat digestion products in solution while constantly replenishing supply of free molecules for absorption
Are micelles absorbed?
No
What happens to fatty acids and monoglycerides after they enter epithelial cells?
They enter smooth endoplasmic reticulum where they form back into triacylglycerols by enzymes
