Why is the hepatic portal system in biology considered to be "portal"?

Question

This question is on systemic circulation, I can't find the answer in my text, medical dictionaries, web, etc. Any help would be appreciated.

Why is the Hepatic Portal System - Portal?

Answer 1

In absolute definition, a portal system is a capillary bed connected to another capillary bed -- but I think this definition doesn't really explain too much. Instead, I would prefer to say that a portal system is kind of like a circulation loop OUTSIDE of the main systemic circulation.

Normally, circulation occurs as originating in the heart, to artery, to capillary bed, to vein, and back to the heart. Well, a portal system has an "artery" leading to it from a capillary bed. In the hepatic portal system, it receives blood from the GI capillary bed in order to sort and filter out many things absorbed from the GI-tract, like food, drugs, etc. This occurs within the hepatic capillary bed, and then returns back to systemic circulation through a vein. In this way, it has its own circulatory loop (i.e. artery, capillary, vein) outside of systemic circulation.

The hypophyseal portal system (i.e. pituitary portal) is similar, but its purpose is to allow endocrine hormones flow from the hypothalamus to the anterior pituitary gland. In this portal system, "arteries" from the hypothalamic capillary bed carry hormones to the capillary bed in the anterior pituitary, with veins that then subsequently lead back to systemic circulation, after the appropriate signals have been delivered. In this way, it is analogous to the hepatic portal system because a circulatory loop (artery, capillary bed, vein) has been set up outside of the systemic circulation.

I know it's difficult to conceptualize -- all I can tell you is to keep thinking about it, and eventually the picture will fall into place. I hope this helped you out some!

Answer 2

Define Hepatic Portal Vein

Answer 3

A portal vein is a vein that connects two systems of capillary beds. Regular veins arise in capillary beds and lead to the heart. In contrast to these, a portal vein does not take blood directly to the heart, but instead, takes blood to second capillary bed system.

In the human body, there are two main instances of portal systems:

Hepatic portal vein - often referred to simply as the portal vein, this vein routes blood from the capillary beds of the gastrointestinal tract into the capillary beds of the liver.

The portal venous system of the pituitary gland.

I hope this helps.

Rick the Pharmacist

Answer 4

First, let's make some definitions clear.

1. Portal = entrance
2. Hepatic Portal System = a venous portal system in which the portal vein receives blood via its tributaries from the capillaries of most of the abdominal viscera and drains it into the hepatic sinusoids

The only thing I can think of is because it's the ENTRANCE to the liver.

funny how it's IMPOSSIBLE to read the minds of those who ask questions. I would hope this answer would suffice.

If asked why the hepatic portal veins are different from other veins ... it's because most veins drain blood to the HEART. The hepati portal veins drain blood to the LIVER.

Answer 5

yup I have right before ending my first marriage. I even had a friend that was interested in helping me. But I was just really starved for attention, confused about my life and well a bit curious. I didn't want to end up hurting her in my confused state so I didn't allow anything to begin. She was sweet and if I was going to switch I would give her a call.