GI Questions 3 - Nutrient Digestion and Absorption 2

Question 1

What form does almost all ingested fat come in?

Answer 1

Triacylglycerols

Question 2

Where does the lipase that is responsible for the fat digestion in the small intestine come from?

Answer 2

Pancreas

Question 3

What makes fat digestion so slow?

Answer 3

Lipase is water soluble so digestion can only take place at the surface of the droplet

Question 4

What does lipase break triacylglycerols down into?

Answer 4

Monoglyceride + 2 fatty acids

Question 5

What is emulsification, and what does it require?

Answer 5

Dividing large lipid droplets into smaller droplets (~1 mm diameter) - increased surface area and accessibility to lipase action
Emulsification requires:
Mechanical disruption of large lipid droplets into small droplets (smooth muscle contraction grinds and mixes lumenal contents)
Emulsifying agents prevent small droplets reforming into large droplets

Question 6

What are the emulsifying agents, what makes them emulsifying agents, how do they work and where do they come from?

Answer 6

The emulsifying agents are bile salts and phospholipids. They are amphipathic molecules - i.e. polar (charged) and nonpolar portions. The nonpolar portions associate with the nonpolar interior of the lipid droplet leaving polar portions exposed at the water surface. Polar portions repel other small lipid droplets (also coated with bile salts/phospholipids) which prevents them reforming into large droplets. Bile salts and phospholipids are secreted in bile.

Question 7

What are micelles, how big are they and how are they absorbed?

Answer 7

Micelles are made up of bile salts, monoglycerides, fatty acids and phospholipids. They’re similar to emulsion droplets but much smaller (4-7um in diameter). Micelles themselves are not absorbed.