Enterohepatic circulation is necessary for the secretion of:
Ref: Pal GK. Biliary secretion. In: Textbook of Medical Physiology. Ahuja Publishing House. 2007; 31: 265. A Ganong v Review of Medical Physiology, 21" edition.Explanation:"Primary function of enterohepatic circulation is to maintain total bile acid pool of the body "Bile MetabolismBile is made up of the bile salts, bile pigments, and other substances dissolved in an alkaline electrolyte solutionAbout 500 ml is secreted per day.Some of the components of the bile are reabsorbed in the intestine and then excreted again by the liver (enterohepatic circulation).The glucuronides of the bile pigments, bilirubin and biliverdin. are responsible for the golden- yellow color of bile.The bile salts are sodium and potassium salts of bile acids, and all those secreted into the bile are conjugated to glycine or taurine, a derivative of cysteine. Blood FlowArteriovenous Oxygen Difference (mL/L)Oxygen ConsumptionResistance (R units )aPercentage of TotalRegionMass(kg)mL/minmL/l00 g/min mL/minmL/100 g/minAbsoluteper kgCardiac OutputOxygen ConsumptionLiver2 5150057 734512.03.59 427 820.4Kidneys0.31260420.014186.04.31.323.37.2Brain1.475054.052453.37.210.113.618.4Skin3.646212.825120 311.742.18.64.8Skeletal muscle31.08402.760500.26.4198.415 520.0Heart muscle0.325084.0114299.721 46.44 711.6Rest of body23.83351 4125440 216.1383 26.217 6whole body63.054008.6462500.41053.0100.0100 0The bile acids are synthesized from cholesterol.The two principal (primary ) bile acids formed in the liver are:- Cholic acid- Chenodeoxvcholic acid.Colonic bacteria convert primary bile acids intoSecondary bile sacids.Cholic acid - Deoxycholic acidChenodeoxycholic acid - Lithocholic acid.Bile acids reduce surface tension along with phospholipids and monoglycerides.They are responsible for the emulsification of fat preparatory to its digestion and absorption in the small intestineThey are amphipathic, ie. they have both hydrophilic and hydrophobic domains:The bile salts tend to form cylindrical disks called micelles, with the hydrophilic surfaces facing out and ihe hydrophobic surfaces facing in.Above a certain concentration called the critical micelle concentration, all bile salts added to a solution form micelles.The micelles play an important role in keeping lipids in solution and transporting them to the brush border of the intestinal epithelial cells, where they are absorbed90-95% bile salts are absorbed from the small intestine.Some are absorbed by nonionic diffusion, but most are absorbed from the terminal ileum by an extremely efficient Na+-bile salt cotransport system powered by basolateral Na+-K+ ATPase.The remaining 5-10% of the bile salts enter the colon and are converted to the salts of deoxycholic acid and lithocholic acid.Lithocholate is relatively insoluble and is mostly excreted in the stools; only 1% is absorbed, but deoxycholate is absorbed.The absorbed bile salts are transported back to the liver in the portal vein and reexcreted in the bile (enterohepatic circulation).Those lost in the stool are replaced by synthesis in the liverThe normal rate of bile salt synthesis is 0.2- 0.4 g/d.The total bile salt pool of approximately 3.5 g
Bile
Gastric fluid
Intestinal secretions
Pancreatic secretions
Liver and Gall Bladder