Hepatic portal system
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202069916
2008-03-30T15:50:44Z
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[[Image:Gray591.png|right|thumb|Diagram showing the hepatic portal vein and its territory.]]
[[Image:Gray1093.png|right|thumb|Microscopic section through a small portal vein branch inside the liver (x250 magnified).]]
In [[human anatomy]], the '''hepatic portal system''' is the system of [[vein]]s that comprises 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]].
==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]] cannot be swallowed because the the liver would inactivate the medication, but it can be taken under the [[tongue]] and thus is absorbed in a way that bypasses the portal venous system.
Blood flow to the liver is unique in that it receives both oxygenated and deoxygenated blood. As a result, the partial pressure of oxygen (pO<sub>2</sub>) 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 [[Liver sinusoid|sinusoids]]. Blood also flows from branches of the [[hepatic artery]] and mixes in the sinusoids to supply the hepatocytes with oxygen. This mixture [[percolation|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]].
Large veins that are considered part of the ''portal venous system'' are the:
*[[Hepatic portal vein]]
*[[Splenic vein]]
Roughly, the portal venous system corresponds to areas supplied by the [[celiac trunk]], the [[superior mesenteric artery]], and the [[inferior mesenteric artery]].
==Pathology==
[[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==
*[[Portal vein]]
*[[Hepatic portal vein]]
*[[Systemic venous system]]
*[[Pulmonary venous system]]
==References==
*William F. Ganong. "Review of Medical Physiology 22nd Edition."
*[http://www.rnceus.com/ld/portsys.htm Hepatic portal system]
*[http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/G/GITract.html Kimball Pages, Hepatic portal system]
[[Category:Veins]]
[[Category:Abdomen]]
{{circulatory-stub}}
{{Veins of the torso}}
[[pl:Układ wrotny wątroby]]
[[pt:Sistema porta hepático]]