27.25 : Bile

Bile is a crucial bodily fluid, characterized by its yellow-green color and alkaline nature. Produced in the liver, it is transported through the common hepatic duct into either the cystic duct, leading to the gallbladder, or directly into the common bile duct. The flow of bile is regulated by the sphincter of Oddi located at the entrance of the duodenum. When this sphincter is closed, bile is redirected to the gallbladder for storage and concentration.

Bile is released when dietary fats enter the duodenum, stimulating the gallbladder to contract and the sphincter of Oddi to relax. This action propels bile into the small intestine, where it plays a pivotal role in digestion. Bile salts aid in lipid digestion by forming micelles, which emulsify dietary lipids, making them easier to break down and absorb. Moreover, the alkaline properties of bile counterbalance the acidity of stomach chyme.

Bilirubin, a yellow pigment derived from the breakdown of hemoglobin in aging red blood cells, is another significant component of bile. Once metabolized in the small intestine, bilirubin is converted into stercobilin, the compound responsible for the brown hue of human feces.

Additionally, bile comprises various electrolytes, cholesterol, triglycerides, and phospholipids.