Enterohepatic circulation and Hepatic Portal circulation

in these slides we discuss about enterohepatic circulation, especially of bile acid ,also the hepatic portal circulation of blood passing through the liver to wards the heart via inferior vena cava and the return of such blood to the liver, and Porta caval Anastomosis(portosystemic Anastomosis) is also discussed.

1. ENTEROHEPATIC CIRCULATION AND HEPATIC PORTAL CIRCULATION By John Stephen

2. ENTEROHEPATIC CIRCULATION 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. Enterohepatic circulation is an especially important concept in the field of  toxicology  as many  lipophilic   xenobiotics  undergo this process causing repeated liver damage.

3. Bile acid:  An acid made by the liver that works with bile to break down fats. On a more technical level, bile acids are steroid carboxylic acids derived from  cholesterol . The primary bile acids are cholic and chenodeoxycholic acids. They are conjugated with glycine or taurine before they are secreted into the bile.

4. Bile salts these are potassium and Sodium salts of conjugated bile acid, bile acid is conjugated with taurine or glycine in the liver Bile ,  also called gall , greenish yellow secretion that is produced in the  liver  and passed to the  gallbladder  for concentration, storage, or transport into the first region of the  small intestine , the  duodenum . Its function is to aid in the  digestion  of  fats  in the duodenum. Bile is composed of bile acids and salts, phospholipids,  cholesterol , pigments, water, and electrolyte chemicals that keep the total solution slightly alkaline (with a pH 7 to 8)

5. Bilirubin ;The breakdown of red blood cells (RBCs) in the body produces bilirubin . The bilirubin travels to the liver and is stored in the gall blader . The body ultimately expels bilirubin in stools. Bilirubin is brown and yellow in color, and it is this pigment that makes feces brown. The RBCs have a lifespan of around 120 days and renew continually. RBCs contain hemoglobin , which helps transport oxygen around the body, and it is this that gets broken down into bilirubin and other substances. The bilirubin is carried to the liver by albumin , a simple protein.

6. Once in the liver, bilirubin becomes " conjugated ." This means it is water-soluble and can be excreted. Unconjugated bilirubin is toxic, but conjugated bilirubin is usually not, because it can be removed from the body, as long as nothing is interfering with its removal. If the liver is not working properly , it may be unable to make bilirubin water-soluble . This may result in too much bilirubin building up in the liver

7. Causes include: viruses, such as  hepatitis  A alcoholic liver disease some medicine overdoses, including acetaminophen autoimmunity, where a disorder of the immune system causes it to attack the cells of the body rather than those that cause disease

8. ENTEROHEPATIC CIRCULATION OF BILE SALT Bile salts are secreted into intestine where they are effectively reabsorbed and thus re used ,In this circulation 94% of bile salts are resent to the liver Bile acids are converted into bile salts in the liver by conjugating them with Glycine / Taurine ,then secreting them in Bile

9. The Bile salts present in Bile are reabsorbed by Na+-BILE SALT COTRANSPORTER which occurs mainly in the ileum This process is Active Transport since bile salts is actively transported out of ileal mucosa cells into portal blood and are then taken up by hepatocytes

10. Since bile salts are Hydrophobic , for them to travel in a portal blood , they are bound to a protein known as Albumin , which carries them in non covalent complex In Conclusion, ENTEROHEPATIC CIRCULATION is a continuos process of bile salts in a bile, their passage into the duodenum ,their absorption in the ileum, and then return to liver Bile salts (single molecule) is used up to 17 times before carried out in the faeces

11. HEPATIC PORTAL CIRCULATION The portal vein is the final common pathway for the transport of venous blood from the spleen, pancreas, gallbladder, and the abdominal part of the gastrointestinal tract. It is formed by the union of the splenic vein and the superior mesenteric vein posterior to the neck of the pancreas at the level of vertebra LII .

12. Ascending towards the liver, the portal vein passes posterior to the superior part of the duodenum and enters the right margin of the lesser omentum . On approaching the liver, the portal vein divides into right and left branches , which enter the liver

13. TRIBUTARIES TO THE PORTAL VEIN The inferior mesenteric vein: drains blood from the rectum, sigmoid colon, and descending colon The superior mesenteric vein: drains blood from the small intestine, cecum , ascending colon, and transverse colon. Posterior to the neck of the pancreas, the superior mesenteric vein joins the splenic vein to form the portal vein. o Tributaries to the superior mesenteric vein include jejunal , ileal , ileocolic , right colic, and middle colic veins.

14. Additional Tributaries include the following; . The right gastro- omental vein , draining the right part of the greater curvature of the stomach. . Gastric vein ; right and left gastric veins draining the lesser curvature of the stomach and abdominal esophagus . Cystic vein ; drains the biliary ducts and the neck of the gallbladder .

15. PORTO SYSTEMIC ANASTOMOSIS Porto systemic anastomosis also known as portal caval anastomosis , The hepatic portal system drains blood from the visceral organs of the abdomen to the liver In normal individuals, 100% of the portal venous blood flow can be recovered from the hepatic veins, whereas in patients with elevated portal vein pressure ( Portal Hypertension ), there is significantly less blood flow to the liver.

16. Causes of Portal Hypertension -liver cirrhosis( interhepatic ) -Thrombosis of Portal vein( extrahepatic ) The rest of the blood enters collateral channels, which drain into the systemic circulation at specific points

17. SITES FOR PORTOCAVAL ANASTOMOSIS Five sites of portal/systemic circulation : 1. Lower third of the Esophagus 2. Paraumbilical Area 3. Upper end of Anal canal 4. Retroperitonial 5. Bare area of liver

18. 1. Lower third of the Esophagus :The esophageal branches of the left gastric vein (portal tributaries) anastomose with the esophageal veins draining the middle third of theesophagus into the azygos veins. (systemic tributaries) 2. Paraumbilical Area They connect the left branch of the portal vein with the superficial veins of the anterior abdominal wall. (systemic tributaries )

19. 3. Anal canal The superior rectal veins (portal tributary) draining the upper half of the anal canal anastomose with the middle and inferior rectal veins (systemic tributaries), which are tributaries of the internal iliac and internal pudendal veins, respectively

20. 4. Retroperitonial The veins of the ascending colon, descending colon, duodenum, pancreas, and liver (portal tributary) anastomose with the renal, lumbar, and phrenic veins (systemic tributaries). 5.Bare area of liver There is some anastomosis between portal venous channels in the liver and azygous system of veins above the diaphragm across the bare area of liver.

21. CONSEQUENCES OF PORTO HYPERTENSION 1.Ascites This is the accumulation of fluid in peritoneal cavity 2.Hemorrhoids Hemorrhoids are painful, swollen veins in the lower portion of the rectum or anus 3.Caput Medusae  is the appearance of distended and engorged superficial epigastric veins, which are seen radiating from the umbilicus across the abdomen 4.Esophageal Varices is the abnormal, enlarged veins in the tube that connects the throat and stomach (esophagus). 

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