This article discusses portal venous systems in general. For the system involving the liver, see
Hepatic portal system.In the
circulatory system of animals, a portal venous system occurs when a
capillary bed drains into another capillary bed through
veins. Both capillary beds and the
blood vessels that connect them are considered part of the portal venous system.They are relatively uncommon as the majority of capillary beds drain into the
heart, not into another capillary bed. Portal venous systems are considered venous because the blood vessels that join the two capillary beds are either
veins or
venules.
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