LIVER BILIARY TRACT 3 Hepato cytes lobules

BILE SECRETION

Normal adult produces 250 to 1100 ml. bile per day.

*  Vagal stimulation increase secretion

*  Stimulation of splanchnic nerves results in decreased bile

   flow

*  Bile  salts  are   very   effective   choleretics   (stimulate

   secretion).

Biliary Secretion

Lobules of the hepatocytes are the source of hepatic bile secretion. Blood flow to the hepatocytes comes from brahches of both the portal vein and the hepatic artery. Blood from the portal vein flows through sinusoids past the hepatocyte to the central vein where it drains into the hepatic veins and inferior vena cava. Only one layer of hepatocutes separates the sinusoids.

Bile is a solution of both organic and inorganic compounds.

The hepatocyte secretes two primary bile acids, cholic acid and chenodeoxycholic acid. These are synthesized in the hepatocyte from cholesterol and recycled through the enterohepatic circulation to conserve bile salts. Primary bile acids, are converted to secondary bile acid (deoxycholic acid and lithocholic acid) when in contact with bacteria in the GIT

Purpose of secretion of bile acids is to allow for the formation of micelles. Micelles are formed and the, bile acid form the outer layer with the fats in the centre so that they will be more soluble in the aqueous medium. The emulsion then move down the gastrointestinal tract and allow lipids that are ingested to freely move in and out of the micelles so that they can be presented to the enterocytes for absorption.

The pigment of bile give it its color, is bilirubin. Bilirubin is derived from the degradation of hemoglobin in the reticuloendothelial system. Because bilirubin itself is not soluble. It is conjugated primarily with glucuronide and occasionally with sulfate. Circulating bilirubin is bound to albumen from which it dissociates at the hepatocyte on the portal venous membrane. It enters the bile canaliculus as bilirubin diglucuronide.

The bile acids, are synthesized or reused by the hepatocutes as they are presented as conjugated and unconjugated bile acids from the portal circulation. The liver produces approximately 500 to 1000 ml of bile per day.

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