bile

Meaning: Bile is made by hepatocytes in the liver, stored and concentrated in the gallbladder, and released through the common bile duct into the duodenum. Its main digestive components are bile salts, made from cholesterol. Bile salts are amphipathic, so they coat large fat globules and break them into tiny droplets (emulsification). This raises the surface area available to pancreatic lipase, and bile salts also form micelles that carry fatty acids and fat-soluble vitamins (A, D, E, K) to the intestinal wall for absorption. Bile also carries bilirubin, a breakdown product of heme, out of the body in feces.

On the MCAT: Expect questions on the pathway and its control. Fat in the duodenum triggers cholecystokinin (CCK), which makes the gallbladder contract. A typical prediction question asks what happens if the bile duct is blocked or the gallbladder is removed: fat digestion and absorption fall, stools contain extra fat, and uptake of fat-soluble vitamins drops. Most bile salts are reabsorbed in the ileum and returned to the liver.

Common confusion: Bile is made in the liver, not the gallbladder, which only stores and concentrates it. Bile salts are not enzymes and do not break covalent bonds. Emulsification is a physical change, while lipase does the chemical hydrolysis of triglycerides.