What is the Difference Between Diastole and Systole

The main difference between diastole and systole is that diastole occurs when the heart relaxes after contraction, whereas systole occurs when the heart contracts to pump the blood out. 

Diastole and systole are two phases of the heart. They allow the heart to pump blood throughout the body.    

Key Areas Covered

1. What is Diastole
– Definition, Types, Function
2. What is Systole
– Definition, Types, Function
3. Similarities Between Diastole and Systole
– Outline of Common Features
4. Difference Between Diastole and Systole
– Comparison of Key Differences

Key Terms 

Diastole, Systole, Atrial Diastole, Ventricular Diastole, Atrial Systole, Ventricular Systole

Difference Between Diastole and Systole - Comparison Summary

What is Diastole

Diastole is the relaxed phase of the cardiac cycle. It allows the refilling of the heart. Typically, the heart rate is 75 beats per minute (bpm). Therefore, one heartbeat lasts for less than one second. The time for the dilation or diastole is 0.5 sec. There are two types of diastoles: atrial diastole and ventricular diastole. In the atrial diastole, the atrium undergoes relaxation, while in the ventricular diastole, the ventricles undergo relaxation. Ventricular diastole has two phases: early ventricular diastole and late ventricular diastole. During the early ventricular diastole, the pressure of the systole drops, opening the mitral valve between the left atrium and left ventricle. It allows the blood in the left atrium to flow into the left ventricle.

Compare Diastole and Systole

Figure 1: Early Ventricular Diastole

Likewise, the tricuspid valve also opens during the early ventricular diastole, flowing the blood in the right atrium to the right ventricle. In the late ventricular diastole, the contraction of the two atrial chambers forces the additional blood flow to the ventricles. During the atrial diastole, the left and the right atria relax and refill with blood.   

What is Systole

Systole is the other phase of the cardiac cycle in which the chambers of the heart contract following the refilling. Ventricular systole takes 0.3 sec. There are two types of systoles: arterial systole and ventricular systole. Arterial systole occurs at the end of the ventricular diastole. Its characteristic feature is the contraction of the myocardium of the left and right atria. During the atrial contraction, the ventricular pressure becomes low, allowing the atrioventricular valves to open: the mitral and tricuspid valves. It flows the blood from the atria to the ventricles.

Diastole vs Systole

Figure 2: Ventricular Systole

Moreover, ventricular systole is the consequence of contractions of the myocardium of the two ventricles. During the ventricular contractions, the pressure inside the ventricles increases, which closes the atrioventricular valves. Also, the pressure rise in the ventricular chambers causes the opening of the pulmonary valves and the aortic valve, respectively, in the right ventricle and in the left ventricle. Additionally, it pumps blood into the pulmonary artery and aorta, respectively. 

Similarities Between Diastole and Systole

  • Diastole and systole are two phases that occur in the heart.
  • They allow to pump blood throughout the body.

Difference Between Diastole and Systole

Definition

Diastole refers to the phase of the heartbeat when the heart muscle relaxes and allows the chambers to fill with blood. In contrast, systole refers to the heartbeat phase when the heart muscle contracts and pumps blood from the chambers into the arteries.

Phase

Diastole is the relaxation of the heart, while systole is the heart’s contraction.

Blood Pressure

Diastolic blood pressure is 80 mm Hg, while systolic blood pressure is 120 mm.

Time

Diastole takes 0.5 sec, while systole takes 0.3 sec. 

Types

Atrial diastole and ventricular diastole are the two types of diastoles, while atrial systole and ventricular systole are the two types. 

Effect on the Heart Muscle

Diastole brings the heart chambers to their normal size to receive blood, while systole decreases the volume of the heart chambers to force the blood out. 

Conclusion

In brief, diastole and systole are two phases of the heart that help to pump blood throughout the body. Diastole is the relaxation of the heart. The diastolic blood pressure is 80 mm of Hg. Importantly, diastole brings the heart chambers to their normal size to receive blood. In comparison, systole is the contraction of the heart. The systolic blood pressure is 120 mm of Hg. Systole reduces the volume of the heart chambers to force the blood out. Therefore, the main difference between diastole and systole is the effect on the heart muscle.

References:
  1. MediLexicon International. (n.d.-c). Understanding blood pressure: What is normal?. Medical News Today. 
Image Courtesy:
  1. Heart diasystole” By Wapcaplet, Reytan. – Own work (CC-BY SA 3.0) via Commons Wikimedia
  2. Heart systole” By Wapcaplet, Reytan, Mtcv – Own Work (CC-BY SA 3.0) via Commons Wikimedia

About the Author: Lakna

Lakna, a graduate in Molecular Biology & Biochemistry, is a Molecular Biologist and has a broad and keen interest in the discovery of nature related things

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