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What is the primary function of the AV node in the heart?

  1. Slows the signal of the SA node for atrial filling

  2. Increases heart rate during exercise

  3. Regulates blood flow from the ventricles

  4. Stimulates the contraction of the ventricles

The correct answer is: Slows the signal of the SA node for atrial filling

The primary function of the AV node, or atrioventricular node, is to slow down the electrical impulses from the SA node (sinoatrial node) before they travel to the ventricles. This delay is critical as it allows the atria to fully contract and push blood into the ventricles before the ventricles contract. If the impulse from the SA node were to reach the ventricles too quickly, it could lead to ineffective filling of the ventricles and inefficient blood circulation. Therefore, the AV node plays a key role in coordinating the timing of the heart's contractions, ensuring effective pumping of blood throughout the body. The other options reflect functions that are not primarily associated with the AV node. For instance, while the heart rate can increase during exercise, it is largely regulated by the SA node and the autonomic nervous system rather than the AV node itself. The AV node does not directly regulate blood flow from the ventricles; rather, it assists in the timing of contractions. Additionally, while ventricular contraction occurs after the delay initiated by the AV node's function, the actual stimulation of ventricular contraction is primarily the role of the bundle of His and the Purkinje fibers, not the AV node itself.