Systole

Systole is the part of the cardiac cycle during which the heart contracts and pumps blood from the chambers into the arteries. This term is usually used in reference to the action of the ventricles.

Overview

The process of systole involves the contraction of the heart muscles, specifically the ventricles, to pump blood into the body's circulatory system. This is in contrast to diastole, the phase of the cardiac cycle during which the heart relaxes and fills with blood.

Phases of Systole

Systole is divided into two phases: isovolumetric contraction and ventricular ejection.

Isovolumetric Contraction

During isovolumetric contraction, the ventricles begin to contract with the closure of the mitral valve and tricuspid valve, which prevents backflow of blood into the atria. However, the aortic valve and pulmonary valve are also closed, so the blood volume in the ventricles remains constant.

Ventricular Ejection

In the ventricular ejection phase, the aortic and pulmonary valves open due to the increased pressure in the ventricles. Blood is then ejected from the ventricles into the aorta and pulmonary artery.

Measurement

The duration of systole can be measured using an electrocardiogram (ECG), which records the electrical activity of the heart. The QRS complex on an ECG corresponds to the depolarization of the ventricles, which initiates systole.

Clinical Significance

Abnormalities in systole can lead to various heart conditions. For example, systolic heart failure occurs when the heart is unable to pump blood effectively during systole. Systolic hypertension refers to high blood pressure during systole.

See Also

• Diastole
• Cardiac cycle
• Heart
• Blood pressure

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