Hepatic portal system - wikipedia Hepatic portal system The hepatic portal vein and its territory Microscopic section through a small portal vein branch inside the liver ( × 250 magnified ) In human anatomy, the hepatic portal system is the system of veins comprising the hepatic portal vein and its tributaries. It is also called the portal venous system, although it is not the only example of a portal venous system, and splanchnic veins, which is not synonymous with hepatic portal system and is imprecise ( as it means visceral veins and not necessarily the veins of the abdominal viscera ). Contents 1 Function 2 Clinical relevance 3 See also 4 References 5 Further reading 6 External links Function The portal venous system is responsible for directing blood from parts of the gastrointestinal tract to the liver. Substances absorbed in the small intestine travel first to the liver for processing before continuing to the heart. Not all of the gastrointestinal tract is part of this system. The system extends from about the lower portion of the esophagus to the upper part of the anal canal. It also includes venous drainage from the spleen and pancreas. Many drugs that are absorbed through the GI tract are substantially metabolized by the liver before reaching general circulation. This is known as the first pass effect. As a consequence, certain drugs can only be taken via certain routes. For example, nitroglycerin can not be swallowed because the liver would deactivate the medication, but it can be taken under the tongue or transdermally ( through the skin ) and thus is absorbed in a way that bypasses the portal venous system. Inversely, dextromethorphan, a cough suppressor, is best taken orally because it needs to be metabolised by the liver into dextrorphan in order to be effective. This latter principle is that of most prodrugs. The use of suppositories is a way to bypass partially the portal vein : the upper 1 / 3 of the rectum is drained into the portal vein while the lower 2 / 3 are drained into the internal iliac vein that goes directly in the inferior vena cava ( thus bypassing the liver ). Blood flow to the liver is unique in that it receives both oxygenated and ( partially ) deoxygenated blood. As a result, the partial gas pressure of oxygen ( pO ) and perfusion pressure of portal blood are lower than in other organs of the body. Blood passes from branches of the portal vein through cavities between `` plates '' of hepatocytes called sinusoids. Blood also flows from branches of the hepatic artery and mixes in the sinusoids to supply the hepatocytes with oxygen. This mixture percolates through the sinusoids and collects in a central vein which drains into the hepatic vein. The hepatic vein subsequently drains into the inferior vena cava. The hepatic artery provides 30 to 40 % of the oxygen to the liver, while only accounting for 25 % of the total liver blood flow. The rest comes from the partially deoxygenated blood from the portal vein. The liver consumes about 20 % of the total body oxygen when at rest. That is why the total liver blood flow is quite high, at about 1 litre a minute and up to two litres a minute. That is on average one fourth of the average cardiac output at rest. Large veins that are considered part of the portal venous system are the : Hepatic portal vein Splenic vein Superior mesenteric vein Inferior mesenteric vein The superior mesenteric vein and the splenic vein come together to form the actual hepatic portal vein. The inferior mesenteric vein connects in the majority of people on the splenic vein, but in some people, it is known to connect on the portal vein or the superior mesenteric vein. Roughly, the portal venous system corresponds to areas supplied by the celiac trunk, the superior mesenteric artery, and the inferior mesenteric artery. Clinical relevance Portal hypertension is a condition in which the blood pressure of the portal venous system is too high. It is often the result of cirrhosis of the liver. See also Systemic venous system Pulmonary venous system References Jump up ^ Splanchnic circulation. Online Medical Dictionary. URL : http://cancerweb.ncl.ac.uk/cgi-bin/omd?splanchnic+circulation. Accessed on : October 22, 2008. Further reading William F. Ganong. `` Review of Medical Physiology 22nd Edition. '' Veins of the abdomen and pelvis To azygos system ascending lumbar subcostal IVC ( Systemic ) To IVC or left renal vein inferior phrenic hepatic central veins of liver liver sinusoid suprarenal renal gonadal ovarian ♀ / testicular ♂ pampiniform plexus ♂ lumbar common iliac Common iliac Unpaired median sacral vein Internal iliac posterior : iliolumbar superior gluteal lateral sacral anterior : inferior gluteal obturator uterine ♀ uterine plexus ♀ vesical vesical plexus prostatic plexus ♂ deep of penis ♂ / clitoris ♀ posterior scrotal ♂ / labial ♀ vaginal plexus / vein ♀ middle rectal internal pudendal inferior rectal bulb of penis ♂ / vestibule ♀ rectal plexus External iliac inferior epigastric deep circumflex iliac vein Portal vein ( Portal ) Splenic short gastric left gastroepiploic pancreatic inferior mesenteric superior rectal left colic Superior mesenteric right gastroepiploic pancreaticoduodenal jejunal ileal middle colic right colic ileocolic appendicular Direct cystic left gastric / esophageal right gastric paraumbilical External links Hepatic portal system Kimball Pages, Hepatic portal system VIRTUAL Liver, an interactive liver anatomy tool ( Contains rich media ; Flash player and Javascript required ) Retrieved from `` https://en.wikipedia.org/w/index.php?title=Hepatic_portal_system&oldid=821223680 '' Categories : Veins Abdomen Hidden categories : All articles with dead external links Articles with dead external links from October 2012 Talk Contents About Wikipedia Español Italiano Kurdî Polski Português Svenska Українська Edit links This page was last edited on 19 January 2018, at 03 : 37. 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Question: the hepatic portal system is composed of blood vessels that bring
Answer: blood from parts of the gastrointestinal tract to the liver