What is an atrium and its function?

• A. A chamber that pumps blood to the lungs
• B. A small chamber in the upper heart; Accept blood and move it with pressure into ventricles
• C. A chamber that stores bile
• D. A valve controlling flow

Answer: (B)

An atrium is one of the two upper heart chambers that receives blood returning to the heart and helps move it into the ventricles. The right atrium collects deoxygenated blood from the body via the superior and inferior vena cavae (and coronary sinus), while the left atrium collects oxygenated blood from the lungs via the pulmonary veins. The atria have thin walls and operate at lower pressure, acting as reservoirs that deliver blood to the ventricles, including a small but important final push known as the atrial kick during filling. This description matches the idea of a small chamber in the upper heart that accepts blood and moves it with pressure into the ventricles. The other options describe the ventricle (pumps blood to the lungs), a bile-storing organ, or a valve, which are not the atria.