Bile salts and their function in lipid digestion

Question 1

What are bile salts?

Answer 1

Bile salts (aka bile acids) act like biological emulsifiers
Derivatives of cholesterol (e.g. taurocholic (taurine) acid and glycholic acid (glycine))
They have a hydrophilic face and hydrophobic face

Question 2

How do bile salts promote emulsification?

Answer 2

Hydrophobic portion binds to and disperses large triglyceride lipid droplets
Hydrophilic portion prevents large lipid droplets from reforming
Increases surface area for triglyceride lipase to act on

Question 3

Define emulsification

Answer 3

The break of large lipid droplets into small uniformly distributed droplets

Question 4

What is a micelle?

Answer 4

A very small lipid aggregate with hydrophilic head groups pointing outwards and hydrophobic tails inwards
Made of bile salts, fatty acids, monoglycerides, phospholipids, cholesterol and fat soluble vitamins

Question 5

Why is it important that bile salts promote micelle formation?

Answer 5

Micelle formation results in efficient digestion and absorption of lipids and lipid-soluble vitamins

Question 6

What is the role of micelles in the digestion of lipids?

Answer 6

Continuously break down and reform each time contents are released
Some are able to diffuse across the intestinal lining
TGs reform in the intestinal lining and are packaged into chylomicrons which enter the blood via lymph

Question 7

What are the three main steps in lipid digestion?

Answer 7

1. Bile salts emulsify fat globules in the intestines
2. Bile salts form micelles with free fatty acids produced from the digestion of emulsion droplets by lipase
3. The absorbed FFAs form triglycerides and are packaged into chylomicrons for secretion in lacteals

Question 8

How are bile salts recycled?

Answer 8

Via enterohepatic circulation
Transporters move bile salts from the digestive tract into the intestinal capillaries where they are then transported to the liver via the portal vein
Hepatocytes take up bile salts from the portal blood and increase bile salt secretion into the bile canaliculi

Question 9

What percentage of bile salts are recycled via the enterohepatic circulation and what percentage is excreted in faeces?

Answer 9

95% recycled

5% excreted