What is enterohepatic circulation?

• A. The hormonal regulation of bile production in the liver.
• B. The recycling pathway in which bile acids are reabsorbed from the intestine and returned to the liver for reuse.
• C. The process of bilirubin conjugation in the liver.
• D. The direct secretion of bile acids into the colon.

Answer: (B)

Entrohepatic circulation is the recycling loop of bile acids: bile acids produced by the liver are released into the gut to aid digestion, then most are reabsorbed from the intestine and returned to the liver to be reused. After aiding fat digestion in the small intestine, particularly in the ileum, bile acids travel back through the portal vein to hepatocytes and are secreted again into bile. This recycling helps conserve bile acids and keep their pool fairly stable. A small amount is excreted in feces, which is the way the body loses bile acids; when loss increases, the liver ramps up synthesis from cholesterol to replace them. The other options don’t describe this cycle: hormonal regulation of bile production isn’t about reusing bile acids, bilirubin conjugation is a separate liver process, and bile acids aren’t directly secreted into the colon.