Blood returning to the mammalian heart in a pulmonary vein drains first into the

(a) right ventricle.
(b) right atrium.
(c) left ventricle.
(d) vena cava.
(e) left atrium.

(E) left atrium.

Explanation:

Pulmonary veins are veins that carry oxygenated blood from the lungs to the heart (left atrium). These veins are part of the pulmonary circuit:

Venae cavae are a vessels (vena cava interior and superior) that carry deoxygenated blood from the body to the right atrium. From the right atrium through the tricuspid valve the blood goes into the right ventricle. Then, from the right ventricle through the pulmonary valve the blood goes into the main pulmonary artery which carries deoxygenated blood to the lungs (to recieve oxygen). Oxygenated blood from the lungs travels to the heart: two pulmonary veins from each lung to the left atrium.

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