Enterohepatic circulation - wikipedia Enterohepatic circulation Enterohepatic circulation of drugs. Not to be confused with the hepatic portal system which directs nutrient rich blood from the intestines to the liver. This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. ( July 2011 ) Enterohepatic circulation refers to the circulation of biliary acids, bilirubin, drugs, or other substances from the liver to the bile, followed by entry into the small intestine, absorption by the enterocyte and transport back to the liver. Contents 1 Biliary acids 1.1 The circuit 1.2 Function 2 Bilirubin 3 Drugs 4 See also 5 References Biliary acids The circuit Hepatocytes metabolize cholesterol to cholic acid and chenodeoxycholic acid. These lipid - soluble bile acids are conjugated ( reversibly attached ) mainly to glycine or taurine molecules to form water soluble primary conjugated bile acids, sometimes called `` bile salts ''. These bile acids travel to the gall bladder during the interdigestive phase for storage and to the descending part of the duodenum via the common bile duct through the major duodenal papilla during digestion. 95 % of the bile acids which are delivered to the duodenum will be recycled by the enterohepatic circulation. Due to the pH of the small intestine, most of the bile acids are ionized and mostly occur as their sodium salts which are then called `` primary conjugated bile salts. '' In the lower small intestine and colon, bacteria dehydroxylate some of the primary bile salts to form secondary conjugated bile salts ( which are still water - soluble ). Along the proximal and distal ileum, these conjugated primary bile salts are reabsorbed actively into hepatic portal circulation. Bacteria deconjugate some of the primary and secondary conjugated bile salts back to lipid - soluble bile acids, which are passively absorbed into hepatic portal circulation. Finally, the conjugated bile acids which remained un-ionized conjugated bile acids are passively absorbed. Venous blood from the ileum goes straight into the portal vein and then into the liver sinusoids. There, hepatocytes extract bile acids very efficiently, and little escapes the healthy liver into systemic circulation. The net effect of enterohepatic recirculation is that each bile salt molecule is reused about 20 times, often multiple times during a single digestive phase. Function The presence of biliary acids in the intestines helps in digestion of fats and other substances. Bilirubin Bilirubin is conjugated with glucuronic acid in the liver by the enzyme glucuronyltransferase, making it soluble in water. Much of it goes into the bile and thus out into the small intestine. Although 95 % of the secreted bile is reabsorbed by the small intestine, conjugated bilirubin is not reabsorbed in small intestine. All conjugated bilirubin in the large intestine is metabolised by colonic bacteria to urobilinogen, which is then further oxidized to urobilin and stercobilin. Urobilin, stercobilin and their degradation products give feces its brown color. However, just like bile, some of the urobilinogen reabsorbed is resecreted in the bile which is also part of enterohepatic circulation. The rest of the reabsorbed urobilinogen is excreted in the urine where it is converted to an oxidized form, urobilin, which gives urine its characteristic yellow color. Drugs Enterohepatic circulation also means that some molecules which would not otherwise be very toxic can become so because of this recycling process. See also Enteroenteric circulation References Jump up ^ Lipoproteins : Lipid Digestion & Transport by Joyce J. Diwan. Rensselaer Polytechnic Institute. Retrieved June 2012 Jump up ^ Kuntz, Erwin ( 2008 ). Hepatology : Textbook and Atlas. Germany : Springer. p. 38. ISBN 978 - 3 - 540 - 76838 - 8. Physiology of the gastrointestinal system GI tract Upper Exocrine Chief cells Pepsinogen Parietal cells Gastric acid Intrinsic factor Foveolar cells HCO Mucus Goblet cells Mucus Processes Swallowing Vomiting Fluids Saliva Gastric acid Lower Enteric nervous system Submucous plexus Myenteric plexus Endocrine / paracrine G cells gastrin D cells somatostatin ECL cells Histamine enterogastrone : I cells CCK K cells GIP S cells secretin Enteroendocrine cells Enterochromaffin cell APUD cell Fluids Intestinal juice Processes Segmentation contractions Migrating motor complex Borborygmus Defecation Either / both Processes Peristalsis ( Interstitial cell of Cajal Basal electrical rhythm ) Gastrocolic reflex Digestion Accessory Fluids Bile Pancreatic juice Processes Enterohepatic circulation Abdominopelvic Peritoneal fluid Biology portal Medicine portal Retrieved from `` https://en.wikipedia.org/w/index.php?title=Enterohepatic_circulation&oldid=782463275 '' Categories : Hepatology Angiology Digestive system Hidden categories : Articles needing additional references from July 2011 All articles needing additional references Talk Contents About Wikipedia Català Deutsch Español Français Nederlands 日本 語 Português Русский Suomi Svenska Українська Edit links This page was last edited on 27 May 2017, at 02 : 11. 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Question: where is bile reabsorbed in the digestive system
Answer: the enterocyte