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The portal vein is not a true vein, because it conducts blood to capillary beds in the liver and not directly to the heart. It is a major component of the hepatic portal system , one of three portal venous systems in the human body; the others being the hypophyseal and renal portal systems.
Blood flow to the liver is unique in that it receives both oxygenated and (partially) deoxygenated blood. As a result, the partial gas pressure of oxygen (pO 2) and perfusion pressure of portal blood are lower than in other organs of the body. Blood passes from branches of the portal vein through cavities between "plates" of hepatocytes called ...
The human hepatic portal system delivers about three-fourths of the blood going to the liver.The final common pathway for transport of venous blood from spleen, pancreas, gallbladder and the abdominal portion of the gastrointestinal tract [2] (with the exception of the inferior part of the anal canal and sigmoid colon) is through the hepatic portal vein.
The portal vein and its branches supply most of the blood and nutrients from the intestine to the liver. [6] Cirrhosis (a form of chronic liver failure) is the most common cause of portal hypertension; other, less frequent causes are therefore grouped as non-cirrhotic portal hypertension.
In humans, the only significant example is the hepatic portal vein which combines from capillaries around the gastrointestinal tract where the blood absorbs the various products of digestion; rather than leading directly back to the heart, the hepatic portal vein branches into a second capillary system in the liver.
The diagnosis of portal vein thrombosis is usually made with imaging confirming a clot in the portal vein; ultrasound is the least invasive method and the addition of Doppler technique shows a filling defect in blood flow. PVT may be classified as either occlusive or nonocclusive based on evidence of blood flow around the clot. [5]
Gastric varices are dilated submucosal veins in the lining of the stomach, which can be a life-threatening cause of bleeding in the upper gastrointestinal tract.They are most commonly found in patients with portal hypertension, or elevated pressure in the portal vein system, which may be a complication of cirrhosis.
A countercurrent exchange system is utilized between the venous and arterial capillaries. Lowering the pH levels in the venous capillaries causes oxygen to unbind from blood hemoglobin because of the Root effect. This causes an increase in venous blood oxygen partial pressure, allowing the oxygen to diffuse through the capillary membrane and ...