What is the portal circulation?

Question

What is the portal circulation?

Answer 1

Portal circulation happens in a tissue when a vein enters the tissue and another vein leaves the tissue.  This happens in the liver for example.

Answer 2

A portal system is a special arrangement of blood vessels in which a capillary bed feeds into veins which in turn feed into another capillary bed. this is unusual as blood from veins usually drains into the heart and not another capillary bed. in the human body, there are two portal systems. the hepatic portal system, which directs blood from the intestines to the liver, and a hypophyseal portal system, which directs blood from the infundibulum to the anterior pituitary.

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