Digestion of Fat, Vitamins and Minerals Flashcards
What form is almost all ingested fat in?
Triacylglycerol
What is responsible for all fat digestion in the small intestine?
Pancreatic lipase
How does triacylglycerol present?
Large lipid droplets which are insoluble in water
What is lipase?
A water soluble enzyme
What does lipase break triacylglycerol into?
Monogylceride and 2 fatty acids
Why is the digestion of fat very slow?
Digestion can only take place at the surface of triacylglycerol droplets
Emulsification
Dividing large lipid droplets into smaller droplets
What is the purpose of emulsification?
To increase the surface area and accessibility to lipase action
What does emulsification require?
- Mechanical disruption
- Emulsifying agent
How does mechanical disruption take place in emulsification?
Large lipid droplets mechanically disrupted into small droplets as smooth muscle contraction grinds and mixes luminal contents
What does the emulsifying agent do?
Prevents small droplets reforming into large droplets
What forms emulsifying agents?
Bile salts and phospholipids secreted in bile
What are emulsifying agents?
Amphiatic molecules (polar and non-polar portions)
How do the amphiatic molecules work as emulsifying agents?
- The non-polar portions associate with non-polar interior of liquid droplet leaving polar portions exposed at water surface
- Polar portions repel other small lipid droplets to prevent reforming into large droplets
How is absorption lipase digestion products enhanced?
By the formation of micelles
What are micelles?
Made up of:
- Bile salt
- Monoglycerides
- Fatty acids
- Phospholipids
How do micelles compare in size to emulsion droplets?
Much smaller
How are the components of micelles arranged?
- Polar portions of molecules a micelle surface
- Non-polar portions form micelle core
What does micelle breakdown result in?
Release of small amounts of free fatty acids and monoglycerides into solution leading to diffusion across plasma membrane of absorbing cells
What does the dynamic equilibrium between fatty acids and monoglycerides in solution and in micelles result in?
Retains most of fat digestion products in solution while constantly replenishing supply of free molecules for absorption
What does not get absorbed with the products of lipase digestion?
Micelles
What happens to fatty acids and monoglycerides after entering epithelial cells?
They enter smooth endoplasmic reticulum where they are reformed into triacylglycerols
What is responsible for the reforming of triacylglycerols?
Enzymes located in the smooth endoplasmic reticulum
What happens to triacylglycerol droplets after they are reformed?
Emulsified by coating of amphiphatic proteins
