![heart blood flow heart blood flow](http://4.bp.blogspot.com/-YL_YK0RBNQ8/UXk9cwY6yhI/AAAAAAAABCg/EMJriQm9vuU/s1600/Heart-Circulation.jpg)
Most circulatory pathways in a fetus are like those in the adult but there are some notable differences because the lungs, the gastrointestinal tract, and the kidneys are not functioning before birth. The capillaries, where the gaseous exchange occurs, merge into venules and these converge to form larger and larger veins until the blood reaches either the superior vena cava or inferior vena cava, which drain into the right atrium. Major Systemic VeinsĪfter blood delivers oxygen to the tissues and picks up carbon dioxide, it returns to the heart through a system of veins. The descending aorta is further subdivided into the thoracic arota and abdominal aorta. This geography divides the aorta into three portions: ascending aorta, arotic arch, and descending aorta. The aorta ascends from the left ventricle, curves posteriorly and to the left, then descends through the thorax and abdomen. Major Systemic ArteriesĪll systemic arteries are branches, either directly or indirectly, from the aorta. The internal iliac artery supplies the pelvic viscera. Branches of the external iliac artery provide the blood supply for the lower extremity. Lumbar arteries provide blood for the muscles and spinal cord. The celiac, superior mesenteric, suprarenal, renal, gonadal, and inferior mesenteric arteries branch from the abdominal aorta to supply the abdominal viscera. The subclavian arteries provide the blood supply for the upper extremity. Blood supply for the brain is provided by the internal carotid and vertebral arteries. The brachiocephalic, left common carotid, and left subclavian arteries branch from the aortic arch. The coronary arteries are the only vessels that branch from the ascending aorta. From the tissue capillaries, the deoxygenated blood returns through a system of veins to the right atrium of the heart. Systemic circulation carries oxygenated blood from the left ventricle, through the arteries, to the capillaries in the tissues of the body. It carries oxygen and nutrients to the cells and picks up carbon dioxide and waste products. The systemic circulation provides the functional blood supply to all body tissue. Then it returns the oxygen-rich blood to the left atrium.
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Pulmonary circulation transports oxygen-poor blood from the right ventricle to the lungs, where blood picks up a new blood supply. The left ventricle is the pump for the systemic circuit, which provides the blood supply for the tissue cells of the body. The pump for the pulmonary circuit, which circulates blood through the lungs, is the right ventricle. The blood vessels of the body are functionally divided into two distinctive circuits: pulmonary circuit and systemic circuit.