Editing Circulatory system (section)

====Portal veins====
{{Main|Portal venous system}}

The general rule is that arteries from the heart branch out into capillaries, which collect into veins leading back to the heart. [[Portal venous system|Portal veins]] are a slight exception to this. In humans, the only significant example is the [[hepatic portal vein]] which combines from capillaries around the [[gastrointestinal tract]] where the blood absorbs the various products of digestion; rather than leading directly back to the heart, the hepatic portal vein branches into a second capillary system in the [[liver]].