The heart's beating process is a carefully orchestrated sequence of electrical and mechanical events, resulting in the pumping of blood throughout the body. The heartbeat consists of the contraction of the atria, followed by the ventricles, causing blood to be pumped to the body. Here's a step-by-step breakdown:
1. Initiation at the Sinoatrial (SA) Node
- The process begins at the SA node, located in the right atrium. This node is often referred to as the heart's natural pacemaker.
- The SA node generates electrical impulses rhythmically. These impulses trigger the heart's contractions.
2. Atrial Contraction
- The electrical impulse spreads across both atria, causing them to contract. This contraction pushes blood into the ventricles.
3. Atrioventricular (AV) Node Delay
- The electrical impulse then reaches the AV node, located between the atria and ventricles.
- The AV node briefly delays the impulse. This delay allows the atria to fully contract and empty their blood into the ventricles before ventricular contraction begins.
4. Ventricular Contraction
- From the AV node, the electrical impulse travels through the specialized fibers called the Bundle of His and through bundle branches to transmit the impulse to the ventricular muscle, resulting in ventricular contraction. This rapid conduction ensures synchronized contraction of the ventricles.
- The ventricles contract, pumping blood out of the heart to the lungs (from the right ventricle) and to the rest of the body (from the left ventricle).
5. Repolarization and Relaxation
- After contraction (systole), the heart muscle repolarizes (recovers its electrical charge) and relaxes (diastole).
- During diastole, the ventricles fill with blood from the atria, preparing for the next heartbeat.
Summary Table: Heartbeat Steps
| Step | Description |
|---|---|
| 1. SA Node Firing | The SA node generates an electrical impulse. |
| 2. Atrial Contraction | The atria contract, pushing blood into the ventricles. |
| 3. AV Node Delay | The AV node delays the impulse, allowing full atrial contraction. |
| 4. Ventricular Contraction | The electrical impulse travels through the Bundle of His and bundle branches, causing ventricular contraction. |
| 5. Repolarization/Relaxation | The heart muscle relaxes and refills with blood. |
