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steroid monocarboxylic acids, derivatives of cholanic acid that are formed in the liver of man and animals and secreted with bile into the duodenum.
In the liver, bile acids are formed predominantly from cholesterol. Bile acids, which are present in different proportions in the bile of different animals, differ only in the number and spatial arrangement of their hydroxyl groups. Human bile contains principally cholic acid and small quantities of deoxycholic, lithocholic, and chenodeoxycholic acids. Very few bile acids are found in a free state in the bile; a large proportion of them are bound in the form of so-called conju-gate acids, such as glycocholic and taurocholic acid, which are formed as a result of the addition of bile acids to glycine and taurine.
Bile acids promote the digestion of fats in the intestinal tract; they activate the lipase of the pancreatic and intestinal juices and promote the emulsification of fats, stimulating their absorption in undecomposed form; they increase the speed of absorption of poorly soluble calcium salts of fatty acids by forming readily soluble complexes with them; and they greatly intensify intestinal peristalsis. In the intestinal tract a large proportion of the bile acid undergoes reverse absorption, and through the portal-vein system it enters the liver, where it is completely retained. The total bile-acid con-tent in the blood averages 0.8 mg percent; in the bile of the liver, 0.9–1.8 percent; and in cystic bile, 5.7–10.8 percent. When there is a considerable increase in the bile-acid content of the blood, the bile acids begin to be discharged with the urine. A decrease in bile-acid content is almost always accompanied by the precipitation of cholesterol, the principal constituent of gallstones.
G. A. SOLOV’EVA