What is the role of the SA node?

• A. To initiate electrical impulses that regulate heartbeats
• B. To anchor valve leaflets
• C. To pump blood
• D. To regulate blood pressure

Answer: (A)

The main idea is that the SA node acts as the heart’s natural pacemaker, initiating the electrical impulses that set the rhythm of the heartbeat. Located in the right atrium near where the superior vena cava enters, its pacemaker cells generate spontaneous depolarizations, producing an impulse that automatically regulates heart rate. Once the SA node fires, the impulse spreads through the atrial muscle, causing atrial contraction, then moves to the AV node and down through the ventricular conduction system to trigger ventricular contraction. This pacing can be adjusted by the autonomic nervous system: sympathetic stimulation speeds up the rate and conduction, while parasympathetic (vagus) activity slows it down. In essence, the SA node’s primary role is to establish and regulate the timing of heartbeats.

The other options don’t fit this role: anchoring valve leaflets is the job of chordae tendineae; pumping blood is accomplished by the ventricles; regulating blood pressure involves overall cardiac output and vascular resistance, not the SA node’s pacing function.