The components of the enterohepatic cycle are the liver, biliary tract, intestine and the portal venous system. Ninety per cent to 95 % of the bile acids entering the gut are actively absorbed in the terminal ileum by a Na-anion co-transporter. The energy for uptake of bile acids is provided by a Na+/K+- ATPase located on the basolateral membrane of the enterocyte. Approximately 500-700 mg are lost per day in the faeces. This is replaced by hepatic synthesis.
There is a total bile acid pool of 2-5 g in the liver. Twenty to 30 g per day of bile acid enters the duodenum, i.e. the bile acid pool recycles 6-10 times in 24 hours through the enterohepatic circulation.
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