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Circulatory System in anatomy and physiology. The course taken by the blood through the arteries, capillaries, and veins back to the heart. In humans and the higher vertebrates, the heart is made up of four chambers. The right and left auricles, or atria, and t ....

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.... pulmonary and systematic circulations described above, a subsidery to the venous system exists, known as portal circulation. A certain amount of blood from the intestine is collected into the portal vein and carried to the liver. Coronary circulation is the means by which the heart tissues themselves are supplied with nutrients and oxygen and are freed of wastes. Just beyond the semiluna valves, two coronary arteries branch from the aorta. Heart action consists of systole and relaxation of the muscular walls of the atria and ventricles. During the period of relaxation, the blood flows from the veins into the two atria. This action is sudden an ....