Bile Salt Recycling in Enterohepatic Circulation
Enterohepatic Circulation
The liver and gallbladder secrete and store bile to aid in digestion.
Additional roles of the liver:
The liver produces and releases bile into the hepatic ducts, which merge to form the common hepatic duct.
Review Biliary Tree
The 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.
Bile 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.
Bile secretion is triggered by hormones that act on the liver and gallbladder; both hormones are secreted by the duodenum in response to chyme.
Secretin acts on the liver to promote bile’s release to the common hepatic duct; secretin is secreted in response to the presence of acidic chyme in the duodenum – the bicarbonate in bile neutralizes the acidity of chyme.
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– as we’ll see, bile salts emulsify lipids.
Bile salts are recycled in the enterohepatic circulation as follows:
Bile salts leave the ileum and are reabsorbed by nearby capillary beds that drain into the hepatic portal system; recall that the hepatic portal system routes venous blood from the digestive system through the liver for processing.
When the bile salts reach the liver, they are recycled and re-secreted into newly formed bile.
A 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.
- Nutrient metabolism
- Synthesis of plasma proteins
- Hormone secretion and modification
- Storage of essential molecules
- Removal of old red blood cells
- Detoxification
Bile
Bile is cholesterol-derived and alkaline.
It contains cholesterol, lecithin (phospholipids), bile pigments, and trace minerals.
Bile is secreted by the liver and stored and concentrated in the gallbladder.
It is released into the digestive tract postprandially (after a meal) when the Sphincter of Oddi opens.
Enterohepatic Circulation & Bile Recycling