Portal venous system

This article is about the portal venous systems in general. For the system involving the liver, see Hepatic portal system.
General diagram of a portal venous system, for example, this occurs in the hypophyseal portal system between the hypothalamus and the anterior pituitary gland.

In the circulatory system of vertebrates, a portal venous system occurs when a capillary bed pools into another capillary bed through veins, without first going through the heart. Both capillary beds and the blood vessels that connect them are considered part of the portal venous system.

Most capillary beds drain into venules and veins which then drain into the heart, not into another capillary bed. 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.[1] Unqualified, portal venous system usually refers to the hepatic portal system. For this reason, portal vein most commonly refers to the hepatic portal vein.

The functional significance of such a system is that it transports products of one region directly to another region in relatively high concentrations. If the heart were involved in the blood circulation between those two regions, those products would be spread around the rest of the body.

  1. ^ Saladin, Kenneth S. (2011). Human anatomy (3rd ed.). New York: McGraw-Hill. p. 571. ISBN 9780071222075.