Bile Acids Are Reabsorbed from the Ileum by a Sodium Co-Transport System
All components of the micelle diffuse into the enterocytes except the bile acids. Bile acids remain in the lumen of the gut, being separated from the other micellar elements as absorption proceeds.
By the time bile acids reach the ileum, they are in a relatively free state, devoid of other lipids. Localized in the ileum is a specific bile acid transport system. This system operates by sodium co-transport and results in the nearly complete reabsorption of bile acids. After absorption, bile acids are transported directly back to the liver by the portal vasculature. The liver efficiently extracts bile acids from the portal blood, so normally the concentration of bile acids in the nonportal blood (systemic circulation) is small. The bile acids extracted by the liver are recycled into the bile. This recycling process occurs repeatedly, so the entire mass of bile acids within the body is circulated through the intestine several times per day.
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