The heart pumps blood through a rhythmic cycle of contractions and relaxations, driven by its muscular walls. This process ensures oxygen-rich blood reaches the body's tissues and oxygen-poor blood is returned to the lungs for re-oxygenation.
The Cardiac Cycle: A Step-by-Step Process
The heart's pumping action, known as the cardiac cycle, involves four key phases:
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Diastole (Relaxation): The heart muscles relax, allowing the chambers (atria and ventricles) to fill with blood. The atria receive blood returning from the body and lungs.
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Atrial Systole (Atrial Contraction): The atria contract, pushing blood into the ventricles. This is a relatively passive process, priming the ventricles for the major pumping event.
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Ventricular Systole (Ventricular Contraction): The ventricles contract powerfully, forcing blood out of the heart. The left ventricle pumps oxygen-rich blood to the body through the aortic valve and the aorta (the body's main artery, as noted in the Cleveland Clinic article). Simultaneously, the right ventricle pumps oxygen-poor blood to the lungs via the pulmonary valve and pulmonary artery (as referenced in the provided text).
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Second Diastole (Relaxation): The ventricles relax, and the cycle begins anew. The heart valves (mitral, tricuspid, pulmonary, and aortic) ensure one-way blood flow throughout the process. The myocardium, a thick muscular layer, is crucial for this squeezing and relaxing action (as explained by the British Heart Foundation).
The Role of Heart Valves
Heart valves are essential for directing blood flow in the correct direction. They prevent backflow, ensuring efficient pumping. The references mention several key valves:
- Mitral Valve: Allows oxygen-rich blood to flow from the left atrium to the left ventricle.
- Aortic Valve: Allows oxygen-rich blood to flow from the left ventricle to the aorta.
- Pulmonary Valve: Allows oxygen-poor blood to flow from the right ventricle to the pulmonary artery.
Understanding the Chambers
The heart has four chambers working in coordination:
- Right Atrium: Receives oxygen-poor blood returning from the body.
- Right Ventricle: Pumps oxygen-poor blood to the lungs.
- Left Atrium: Receives oxygen-rich blood from the lungs.
- Left Ventricle: Pumps oxygen-rich blood to the body. This chamber is the strongest, as it needs to propel blood throughout the entire body.
