THREE PRINCIPAL VENOUS SYSTEMS

follow, unlike the arterial system. However, the larger veins are commonly located parallel to the course taken by their counterpart in the arterial system. For instance, the renal vein parallels the renal artery, the common iliac vein parallels the common iliac artery, and so forth. THREE PRINCIPAL VENOUS SYSTEMS.— The three principal venous systems in the body are the pulmonary, portal, and systemic. · The pulmonary system is composed of four vessels, two from each lung, which empty into the left atrium. These are the only veins in the body that carry freshly oxygenated blood. · The portal system consists of the veins that drain venous blood from the abdominal part of the digestive 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. The blood in the portal system conveys absorbed substances from the intestinal tract to the liver for storage, 1-30 HM3F0136C LEFT INNOMINATE LEFT SUBCLAVIAN CEPHALIC BASILIC INTERNAL JUGULAR EXTERNAL JUGULAR RIGHT SUBCLAVIAN COMMON ILIAC FEMORAL CUBITAL MEDIAN INTERNAL ILIAC (HYPOGASTRIC) EXTERNAL ILIAC GREAT SAPHENOUS INFERIOR VENA CAVA SUPERIOR VENA CAVA RIGHT INNOMINATE Figure 1-36.—Principal vessels of the venous system.