Does the hepatic portal system form capillary beds? If so, is the capillary bed coordinated with that of arterial capillaries?
What review paper might I look in?
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2 Answers
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In anatomy, a "portal circulation" is simply when you have a capillary bed that is interposed between two venous circulations BEFORE blood flows back to the heart. There are a couple of places in the body where this occurs, including the liver (hepatic portal system) and the pituitary (hypophyseal portal system).
To answer your question... yes, the hepatic portal circulation drains into the liver sinusoids, which is one large capillary circulation.
The hepatic arteries and portal vein give off branches that make up the portal triad which delivers blood (both arterial and venous blood) to the functional units of the liver which are the hepatic lobules.
The hepatic portal system drains into the liver and forms a highly fenestrated network of capillary beds within the liver parenchyma. In the case of the hepatic portal circulation, the flow through the liver sinusoids is considered this capillary bed. In humans, the flow of blood that makes up the hepatic portal circulation is mostly venous blood from the gastrointestinal tract. This allows blood to flow through the liver for clearance of substances like drugs and hormones before those substances reach the peripheral circulation. Specifically, arterial blood flows to the majority of the stomach, small intestine and colon from the celiac, superior and inferior mesenteric arteries. This arterial blood flows through the capillary beds in the mesenteric circulation (i.e. the capillary beds around the intestinal enterocytes) and then into the major veins that drain the intestinal tract. There are two major veins that drain the intestinal tract, the superior and inferior mesenteric veins. The inferior mesenteric vein drains into the splenic vein and then the splenic vein and superior mesenteric veins merge to form the portal vein of the liver. Once blood flows into the portal vein it flows through the hepatic sinusoids (another capillary bed) before flowing out of the hepatic veins into the inferior vena cava, and then back into the heart.
The figure below is a picture of the intestinal veins from Gray's Anatomy (wikipedia) that form the hepatic portal vein, the superior and inferior mesenteric as well as the splenic vein. In the figure the older term lienal vein is used instead of splenic vein. The latin word for spleen is lineal.
The picture below is a schematic of the hepatic lobule that receives its blood from a portal triad. In the center of the lobule is the "central vein". The blood flows from the portal triad to the central vein, and then the central veins coalesce to form the hepatic veins (which then drain into the inferior vena cava). The picture below is available from this website, along with some other text and picture for more information.
And another nice picture from wikipedia on "hepatic lobules".
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As for a "freely available review" that you asked for, I can't find any with better pictures from PubMed that what is already in this answer.
answered Mar 1, 2016 at 3:07
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This picure is from Junqueira histology book:
as it shows a branch of hepatic portal vain and a branch of hepatic artery form hepatic sinusoid which is some sort of capillaries. hope it helps :)
