Why is a portal circulation a "strange" circulation?

Question

I know what the function of this circulation is, however my professor is asking us as to why it is a "strange" circulation? I can not figure this out...please help!

Answer 1

In most circulation, the blood goes from the heart to the aorta to the arteries, to the organ or tissue, to the veins and back to the heart.
In a portal circulation, the blood goes from the heart to the aorta to the arteries, to the organ or tissue, to a vein, then to another tissue or organ BEFORE it goes back to the heart.
An example of this is the blood that goes through the anterior mesenteric artery to the small intestine, goes through the mesenteric vein to the hepatic portal vein, and to the liver, before it returns to the heart.
This is because the blood coming from the intestines has a lot of sugar that it absorbed. The body tries to keep the level of sugar in the blood the same at all times. So, the blood goes to the liver, where it stores some of the sugar, before it goes back to the heart and through the rest of the circulation. Then, in the middle of the night, when you haven't eaten anything in a while (and the level of sugar in your blood is low), some of that sugar that was stored in the liver is released back to the blood.

Answer 2

To Date: None!