The heart is divided into four chambers (see fig. 1). The two upper chambers are the atria, and are separated into the right and left atrium by a wall of tissue called the atrial septum. The two lower chambers are the ventricles, and are separated into the right and left ventricle by the ventricular septum.
The right atrium receives blood from the body via the superior vena cava and the inferior vena cava (see fig. 2). Blood flows from the right atrium to the right ventricle. The blood is then pumped by the right ventricle to the lungs where it picks up oxygen. Blood returns to the left atrium, flows into left ventricle and then is pumped out to the body.
Figure 1: Chambers of the heart.
Figure 2: The right atrium with superior and inferior vena cava.
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