{"id":"1618","type":{"id":"7","name":"Physiologic Processes","urlId":"physiological-process","subtypes":[],"schema":"http:\/\/schema.org\/Article","numTerms":0},"subtype":{"id":"64","name":"Digestive Physiology","urlId":"digestive"},"urlId":"enterohepatic-circulation","role":"term","course":{"id":"3","urlId":"physiology","name":"Physiology"},"children":[],"name":"Enterohepatic Circulation","demo":0,"description":"The liver and gallbladder secrete and store bile to aid in digestion.\n\nAdditional roles of the liver: \n* Nutrient metabolism\n* Synthesis of plasma proteins\n* Hormone secretion and modification\n* Storage of essential molecules\n* Removal of old red blood cells\n* Detoxification\n\n## Bile\n\nBile is cholesterol-derived and alkaline.\n\nIt contains cholesterol, lecithin (phospholipids), bile pigments, and trace minerals.  \n\nBile is secreted by the liver and stored and concentrated in the gallbladder. \n\nIt is released into the digestive tract postprandially (after a meal) when the Sphincter of Oddi opens.\n\n\u003E ### **Enterohepatic Circulation \u0026 Bile Recycling**\n\nThe liver produces and releases bile into the hepatic ducts, which merge to form the common hepatic duct. \n\nReview [Biliary Tree](\/term\/gross-anatomy\/biliary-and-pancreatic-ducts)\n\nThe gallbladder stores bile; it sits below the liver, and is drained by the cystic duct; the cystic and common hepatic ducts merge to form the common bile duct. \n\nBile exits the biliary system of ducts and enters the duodenum of the small intestine; the Sphincter of Oddi (aka hepatopancreatic sphincter), regulates passage of bile from the common bile duct to the duodenum. \n\nBile secretion is triggered by hormones that act on the liver and gallbladder; both hormones are secreted by the duodenum in response to chyme.  \n\n**Secretin** acts on the liver to promote bile\u2019s release to the common hepatic duct; secretin is secreted in response to the presence of acidic chyme in the duodenum \u2013 the bicarbonate in bile neutralizes the acidity of chyme. \n\n**CCK (cholecystokinin)** stimulates gallbladder contraction and release of bile; it also works on the Sphincter of Oddi to allow bile to move from the common bile duct to the duodenum. CCK is secreted in response to fatty acids in the duodenum\u2013 as we\u2019ll see, bile salts emulsify lipids. \n\nBile salts are recycled in the enterohepatic circulation as follows:\n\nBile salts leave the ileum and are reabsorbed by nearby capillary beds that drain into the hepatic portal system; recall that the [hepatic portal system](\/term\/gross-anatomy\/veins-hepatic-portal-system) routes venous blood from the digestive system through the liver for processing. \n\nWhen the bile salts reach the liver, they are recycled and re-secreted into newly formed bile. \n\nA small portion, about 5%, of bile salts escape this pathway and are excreted in the feces.  The liver synthesizes new bile salts to account for this loss. 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