follow, unlike the arterial system. However, the largerveins are commonly located parallel to the coursetaken by their counterpart in the arterial system. Forinstance, the renal vein parallels the renal artery, thecommon iliac vein parallels the common iliac artery,and so forth.THREE PRINCIPAL VENOUS SYSTEMS.—The three principal venous systems in the body are thepulmonary, portal, and systemic.The pulmonary system is composed of fourvessels, two from each lung, which empty into the leftatrium. These are the only veins in the body that carryfreshly oxygenated blood.The portal system consists of the veins thatdrain venous blood from the abdominal part of thedigestive tract—the spleen, pancreas, and gallbladder,but not the lower rectum—and deliver it to the liver.There, it is distributed by a set of venous capillaries. Theblood in the portal system conveys absorbed substancesfrom the intestinal tract to the liver for storage,1-30HM3F0136CLEFTINNOMINATELEFTSUBCLAVIANCEPHALICBASILICINTERNALJUGULAREXTERNALJUGULARRIGHTSUBCLAVIANCOMMONILIACFEMORALCUBITALMEDIANINTERNAL ILIAC(HYPOGASTRIC)EXTERNALILIACGREATSAPHENOUSINFERIORVENA CAVASUPERIORVENA CAVARIGHTINNOMINATEFigure 1-36.—Principal vessels of the venous system.
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