Transcription: The heart is a pump which must circulate blood through two different but interconnected vascular systems. The smaller of these systems is the pulmonary system. Blood returning from the upper part of the body is delivered to the right atrium of the heart by the superior vena cava, one of the body's two largest veins, while blood returning from the lower part of the body is delivered to the right atrium by the other major vein, the inferior vena cava. Contraction of the right atrium in each cardiac cycle forces blood into the right ventricle. This is followed by contraction of the right ventricl ...
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