What is the primary function of the sinoatrial (SA) node in the heart?

The sinoatrial (SA) node's primary function is to control the heart rate. It serves as the natural pacemaker of the heart, generating electrical impulses that initiate each heartbeat. This electrical activity first causes the atria to contract, pushing blood into the ventricles. The rate at which the SA node fires impulses determines how fast or slow the heart beats, hence directly influencing heart rate.

While initiating heart muscle contractions is a secondary aspect of its function, as the contractions result from the signals generated, the main role revolves around the regulation of the heart's rhythm and frequency. Additionally, the SA node does not regulate blood pressure directly; blood pressure is influenced by a combination of factors including cardiac output and vascular resistance. Similarly, while the SA node plays a role in coordinating electrical signals, its primary and most crucial function is the control of heart rate, thereby ensuring effective blood circulation throughout the body.