Understanding Systole: The Heart's Contraction Phase

Systole is a fundamental component of the cardiac cycle and a key phase in the heart's pump function. This article aims to provide a comprehensive understanding of systole, its role in blood pressure measurement, and the physiological processes associated with it.

What is Systole?

During systole, the heart muscle contracts. This contraction is crucial as it propels blood from the heart into the large blood vessels of the circulatory system, which then directs the blood to every organ and tissue in the body. The systole period specifically refers to the ventricular contraction phase, which occurs between the first and second heart sounds (lub-dub) within the cardiac cycle.

The QRS complex on an electrocardiogram (ECG or EKG) marks the beginning of ventricular systole. Ventricular systole lasts typically between 0.3 to 0.4 seconds and involves the ejection of about 80 to 100 cubic centimeters of blood from each ventricle into the aorta and pulmonary trunk. During this phase, arterial blood pressure rises to its peak, known as systolic blood pressure, which in humans is normally around 90 to 120 millimeters of mercury (mmHg).

Blood Pressure Measurement

When doctors conduct a blood pressure check, the upper reading is the systolic pressure, and the lower reading is the diastolic pressure. For instance, a reading of 130/80 indicates that the systolic pressure is 130 mmHg and the diastolic pressure is 80 mmHg. This relationship between the systolic and diastolic pressures reflects the heart's pumping action during systole and its relaxation during diastole.

During systole, blood pressure is at its peak. It's important to understand the significance of the systolic pressure, as it provides insights into the force of each heartbeat. Elevated systolic blood pressure can indicate a higher risk of cardiovascular diseases. Monitoring systolic pressure is a critical aspect of maintaining heart health and overall well-being.

Contrast with Diastole

Diastole, the opposite phase of the cardiac cycle, is characterized by the relaxation of the heart muscle. During diastole, the heart refills with blood, which is a preparatory phase for the next contraction (systole). Unlike systole, during diastole, blood pressure decreases.

Atrial systole, occurring near the end of ventricular diastole, also plays a role in filling the ventricles. This phase is marked by the P wave on the ECG, indicating atrial contraction and subsequent filling of the ventricles with blood.

Additional Insights

A systole in the context of protozoans, such as amoebas, refers to the contraction of a specialized structure called the contractile vacuole, which helps in the regulation of water balance within the cell.

References

Verywell Health - Systole and Diastole
MedicineNet - Systole Definition and Grades
WebMD - Understanding BP Measurement