The hepatic portal system is strange but not unique. It is one of the two portal systems in the body. Most organs have an arterial supply, a single capillary bed, and a single venous drainage that delivers blood to the superior or inferior vena cava. The hepatic portal system is strange because the portal system is interposed between two capillary systems ( the digestive system and the liver) before the blood enters the final hepatic drainage ( right, middle and left hepatic veins) which finally returns the the blood to the inferior vena cava.
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Blood supply to most organs and systems involves an arterial blood supply, a capillary exchange net work and a single venous drainage that delivers blood to a vena cava. The hepatic portal system is strange-- but not unique-- in that it is interposed between two capillary beds--there is also a hypotahlamo-hypophyseal portal system between the hypothalamus and the anterior pituitary gland. The Hepatic Portal System: The first capillary network of this system is in organs of the digestive system.. Venous drainage from these organs is carried by tributaries that unite to form the hepatic portal vein. These tributaries include the splenic vein ( drains stomach and pancreas), the inferior mesenteric vein ( drains drains colon and rectum), and the superior mesenteric vein ( drains small intestine, ascending and transverse colon, and stomach). Blood from the portal vein and blood from he hepatic artery percolate together through the capillaries and sinusoid of the liver. The hepatocytes remove toxins and waste substances and process nutrients, while phagocytes remove pathogenic microorganisms and debris. The venous blood is then returned to the general circulation by the three hepatic veins--left, middle and right..