A Level Biology Practice Exam

What is the primary function of the sino-atrial node (SAN) in the heart?

1. To pump blood throughout the body

2. To initiate a wave of excitation triggering heart contractions

3. To control blood pressure

4. To receive oxygenated blood from the lungs

The correct answer is: To initiate a wave of excitation triggering heart contractions

The sino-atrial node (SAN) serves as the heart's natural pacemaker, playing a crucial role in coordinating heart rhythm. Its primary function is to initiate a wave of excitation, which triggers the contraction of the heart. This process begins when the SAN generates electrical impulses that spread through the atria, causing them to contract and push blood into the ventricles. The SAN's ability to generate these impulses is vital for maintaining a regular heartbeat, and it is influenced by various factors such as hormones and the autonomic nervous system. By ensuring that these electrical signals are properly initiated, the SAN effectively regulates the heart's rhythm, influencing overall blood circulation throughout the body. The other choices describe functions not associated with the sino-atrial node. The pumping of blood is performed by the heart's chambers (the ventricles), rather than by the SAN directly. Controlling blood pressure involves a complex interplay of various systems, including the autonomic nervous system and hormones, but is not the primary role of the SAN. Similarly, receiving oxygenated blood from the lungs is the responsibility of the heart's chambers, particularly the left atrium, rather than the SAN.