One of the composition of bile along with bile acids, phospholipids, cholesterol, pigments, water, and electrolyte chemicals. Bile salts and acids can be synthesized from cholesterol or extracted from the bloodstream by the liver.
Bile salts (conjugated bile acids) are composed of the salts of four different kinds of free bile acids (cholic, deoxycholic, chenodeoxycholic, and lithocholic acids). And each of these acids may in turn be conjugated with glycine or taurine by liver cells to form more complex acids and salts. Once secreted into the lumen of the intestine, they are modified by gut bacteria. They are partially dehydroxylated and their glycine and taurine groups are removed.
They pass from the liver into the duodenum, where they act as detergents to emulsify fat and reduce the surface tension on fat droplets to prepare them for the action of pancreatic and intestinal fat-splitting enzymes. The solubilized ingested fat and fat-soluble vitamins are prepared for digestion and absorption.
They are large, negatively charged ions that are not readily absorbed by the upper region of the small intestine. Consequently, they remain in the small intestine until most of the fat is digested. In the lower small intestine (ileum), the salts and acids are absorbed and passed back into the bloodstream until they are once again extracted by the liver (enterohepatic circulation).
They do not normally reach the colon. When they do, however, they may inhibit the absorption of water and sodium, causing a watery diarrhea.
Bile salts and acids are transported in a fluid that contains water, sodium, chloride, and bicarbonates. This fluid is produced in the liver, and it serves to neutralize hydrochloric acid passed from the stomach into the duodenum. Water-insoluble wastes that the liver removes from blood, such as cholesterol, steroids, drugs, and hemoglobin pigments (e.g. bilirubin), are carried in the fluid to the excretory system. Traces of other substances can also be found in bile including mucus, serum proteins, lecithin, neutral fats, fatty acids, and urea.
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