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por·tal sys·tem
/ˈpôrdl ˈsistim/noun
- 1. the system of blood vessels consisting of the portal vein with its tributaries and branches.
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In human anatomy, the hepatic portal system or portal venous system is the system of veins comprising the portal vein and its tributaries. The other portal venous systems in the body are the renal portal system , and the hypophyseal portal system .
The hypophyseal portal system is a system of blood vessels in the microcirculation at the base of the brain, connecting the hypothalamus with the anterior pituitary. Its main function is to quickly transport and exchange hormones between the hypothalamus arcuate nucleus and anterior pituitary gland. The capillaries in the portal system are ...
There are three portal systems, two venous: the hepatic portal system and the hypophyseal portal system; and one arterial (one capillary system between two arteries): the renal portal system. Unqualified, portal venous system usually refers to the hepatic portal system.
The portal vein is not a true vein, because it conducts blood to capillary beds in the liver and not directly to the heart. It is a major component of the hepatic portal system, one of three portal venous systems in the human body; the others being the hypophyseal and renal portal systems.
A renal portal system is a portal venous system found in reptiles, and fish excluding hagfish and lampreys. It is not found in mammals . [1] Its function is to supply blood to renal tubules when glomerular filtration is absent or downregulated.
The causes for portal hypertension are classified as originating in the portal venous system before it reaches the liver (prehepatic causes), within the liver (intrahepatic) or between the liver and the heart (post-hepatic). The most common cause is cirrhosis (chronic liver failure).
Portal venous pressure is the blood pressure in the hepatic portal vein, and is normally between 5-10 mmHg. [1] Raised portal venous pressure is termed portal hypertension, [2] and has numerous sequelae such as ascites and hepatic encephalopathy. [3] [4]
Illustration showing the hepatic portal vein system. The first pass effect (also known as first-pass metabolism or presystemic metabolism) is a phenomenon of drug metabolism at a specific location in the body which leads to a reduction in the concentration of the active drug before it reaches the site of action or systemic circulation.
Porto-systemic anastomosis Portal caval system. A portacaval anastomosis or portocaval anastomosis is a specific type of circulatory anastomosis that occurs between the veins of the portal circulation and the vena cava, thus forming one of the principal types of portasystemic anastomosis or portosystemic anastomosis, as it connects the portal ...
The Solar System is the gravitationally bound system of the Sun and the objects that orbit it. It was formed 4.6 billion years ago when a dense region of a molecular cloud collapsed, forming the Sun and a protoplanetary disc .
