Large lipid droplets present an obstacle to digestion in the water environment of the small intestine, so bile salts emulsify them to form smaller droplets.
Bile salts have hydrophobic and hydrophilic sides (they are amphipathic molecules):
- The hydrophobic portion is a cholesterol precursor, composed of mainly non-polar hydrocarbons that can interact with lipid droplets.
- The hydrophilic side is studded with polar hydroxyl and carboxyl groups, which can be exposed to the aqueous environment.
Fat emulsification: large lipid droplets, which are hydrophobic, are exposeed to bile salts and phospholipids. These emulsifying agents break the large droplet into smaller droplets of triglycerides.
Now, digestion can occur: lipase, with the help of colipase, can break
triglycerides into their smaller components: a monoglyceride (glycerol) and two fatty acids.
These small molecules can be absorbed by the small intestine in the form of micelles.
Micelles are water-soluble units that act as holding stations for the lipids for transport out of the small intestine.
They have a spherical arrangement: the fatty acids and triglycerides are on the inside, and the bile salts are on the outside. We use double-sided arrows to show that these micelles are continuously formed and broken.
