Bile salts are steroids with detergent properties which are used to emulsify lipids in foodstuff passing through the intestine to enable fat digestion and absorption through the intestinal wall. They are secreted from the liver stored in the gall bladder and passed through the bile duct into the intestine when food is passing through.
Biosynthesis represents the major metabolic fate of cholesterol, accounting for more than half of the 800mg/day of cholesterol that the average adult uses up in metabolic processes. By comparison, steroid hormone biosynthesis consumes only about 50 mg of cholesterol per day. Much more that 400 mg of bile salts is required and secreted into the intestine per day, and this is achieved by re-cycling the bile salts.
Most of the bile salts secreted into the upper region of the small intestine are absorbed along with the dietary lipids that they emulsified at the lower end of the small intestine. They are separated from the dietary lipid and returned to the liver for re-use. Re-cycling thus enables 20-30g of bile salts to be secreted into the small intestine each day.
The most abundant of the bile salts in humans are cholate and deoxycholate, and they are normally conjugated with either glycine or taurine to give glycocholate or taurocholate respectively. The conjugation is important in identifying the bile salt for re-cycling back to the liver.