Which of the following statements is correct in reference to heart function?

• A. The sinoatrial node acts as the natural pacemaker of the heart.
• B. The atrioventricular node directly stimulates the ventricles to contract.
• C. The right atrium receives oxygenated blood from the lungs.
• D. The left ventricle pumps blood into the pulmonary circulation.

Answer: (A)

Verified step by step guidance

1. Identify the role of the sinoatrial (SA) node in heart function. The SA node is known as the natural pacemaker of the heart because it initiates the electrical impulses that set the rhythm for the heart to beat.
2. Understand the function of the atrioventricular (AV) node. The AV node receives impulses from the SA node and relays them to the ventricles, but it does not directly stimulate the ventricles to contract. Instead, it passes the impulse to the bundle of His and Purkinje fibers, which then stimulate ventricular contraction.
3. Clarify the blood flow into the right atrium. The right atrium receives deoxygenated blood from the body through the superior and inferior vena cavae, not oxygenated blood from the lungs.
4. Examine the role of the left ventricle. The left ventricle pumps oxygenated blood into the systemic circulation through the aorta, not into the pulmonary circulation.
5. Conclude by identifying the correct statement: The sinoatrial node acts as the natural pacemaker of the heart, which is the accurate description of its function in heart physiology.