THE CARDIAC CYCLE AND HEART SOUNDS

INTRODUCTION: The cardiac cycle is the sequence of events in one heartbeat. In its simplest form, the cardiac cycle is the simultaneous contraction of the two atria, followed a fraction of a second later by the simultaneous contraction of the two ventricles. Systole is another term for contraction. The term for relaxation is diastole. You are probably familiar with these terms as they apply to blood pressure readings. If we apply them to the cardiac cycle, we can say that atrial systole is followed by ventricular systole. There is, however, a significant difference between the movement of blood from the atria to the ventricles and the movement of blood from the ventricles to the arteries.

THE SEQUENCE OF BLOOD FLOW: Blood is constantly flowing from the veins into both atria. As more blood accumulates, its pressure forces open the right and left AV valves. Two-thirds of the atrial blood flows passively into the ventricles; the atria then contract to pump the remaining blood into the ventricles. Following their contraction, the atria relax and the ventricles begin to contract. Ventricular contraction forces blood against the flaps of the right and left AV valves and closes them; the force of blood also opens the aortic and pulmonary semilunar valves. As the ventricles continue to contract, they pump blood into the arteries. The ventricles then relax, and at the same time blood continues to flow into the atria, and the cycle begins again.

CHARACTERISTICS OF THE BLOOD FLOW: The important distinction here is that most blood flows passively from atria to ventricles, but all blood to the arteries is actively pumped by the ventricles. For this reason, the proper functioning of the ventricles is much more crucial to survival than is atrial functioning. The cardiac cycle is this precise sequence of events that keeps blood moving from the veins, through the heart, and into the arteries. The cardiac cycle also creates the heart sounds: Each heartbeat produces two sounds, often called lubdup, that can be heard with a stethoscope. The first sound, the loudest and longest, is caused by ventricular systole closing the AV valves. The second sound is caused by the closure of the aortic and pulmonary semilunar valves. If any of the valves do not close properly, an extra sound called a heart murmur may be heard.

RELATED;

1.  CHAMBERS AND CIRCULATION THROUGH THE HEART

2.  ANATOMY AND PHYSIOLOGY

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