Atria are the two upper chambers that receive blood returning to the heart.

Atria are the two upper chambers that receive blood returning to the heart.

• A. Two lower chambers that pump blood into arteries
• B. The outer covering of the heart
• C. Two upper chambers that receive blood returning to the heart
• D. The valves between the atria and ventricles

Answer: (C)

Atria are the two upper chambers that receive blood returning to the heart. The right atrium collects deoxygenated blood from the body through the superior and inferior vena cavae (and coronary sinus), while the left atrium collects oxygenated blood from the lungs through the pulmonary veins. Their walls are thinner because they operate at lower pressures, simply gathering blood and passing it to the ventricles below through the atrioventricular valves (tricuspid on the right, mitral on the left). This description directly matches the idea that the atria are the receiving chambers. The other statements describe the ventricles, the heart’s outer covering, or the valves themselves, not the atria.

Atria are the two upper chambers that receive blood returning to the heart. The right atrium collects deoxygenated blood from the body through the superior and inferior vena cavae (and coronary sinus), while the left atrium collects oxygenated blood from the lungs through the pulmonary veins. Their walls are thinner because they operate at lower pressures, simply gathering blood and passing it to the ventricles below through the atrioventricular valves (tricuspid on the right, mitral on the left). This description directly matches the idea that the atria are the receiving chambers. The other statements describe the ventricles, the heart’s outer covering, or the valves themselves, not the atria.