Cholehepatic shunt

Figure 2.3 Absorption of bile acids by the cholangiocyte in the cholehepatic shunt. Bile acids are absorbed at the apical membrane of the cholangioc5de by the apical sodium-dependent bile-acid transporter (ASBT) that causes cholehepatic shunting of bile acids back to the hepatocyte. Absorbed bile adds are exported across the basolateral membrane by multi-drug-resistance-associated protein 3 (MRP3), a truncated form of ASBT or by the het-eromeric organic solute (OST) a and p forms. Bile adds cause choleresis that is rich in bicarbonate ions secreted by the chloride/bicarbonate ion exchanger.

The tertiary bile acids are formed in the liver as well as in the gut. (s. fig. 3.3) Intestinally absorbed lithocholic acid is enzymatically converted to sulpholitho-cholic acid in the liver. Ketolithocholic acid is transformed to (hypercholeretic) ursodeoxycholic acid in both the intestine and the liver. When passing through the canaliculi, UDC is partly reabsorbed by epithelial cells and returned to the liver via the blood circulation (= cholehepatic shunt). (41) The latter is chemically and structurally identical to chenodeoxycholic acid, of which it is deemed to be the 7P-epimer ... 

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