Diastole: Definition & Importance

Instructor: Adrianne Baron

Adrianne has a master's degree in cancer biology and has taught high school and college biology.

We are going to discuss what diastole means and when it occurs. You will learn about the importance of diastole. There will be a quiz to check your understanding after the lesson.

What Does Diastole Mean?

You may have had the experience of lifting weights at some point in your lifetime. If you have done this or even watched someone else lift weights, then you know that there are two things that happen during weightlifting. The person contracts their arm muscles in order to carry out the function of lifting the weights. The other thing that happens is the person relaxing arm muscles in order to carry out the function of lowering the weights. This two part process would be considered one cycle of weightlifting.

The heart works in a similar way since it is also a muscle. The heart muscle contracts to carry out the function of pushing blood out and then it relaxes in order to allow blood back in. This is one heart cycle or heartbeat. When the heart muscle contracts this is called systole. The relaxation of the heart muscle is known as diastole.

Keep in mind that the heart has two upper chambers, called the atria, that contract and relax together. When the atria relax, it is atrial diastole. The heart also has two lower chambers, called the ventricles, that contract and relax together. Ventricular diastole is when the ventricles relax.

The Importance of Diastole

Blood moves in this direction through the heart during systole and diastole.
Diagram showing how blood flows through the heart

When the chambers of the heart are in systole, they are contracted and therefore the chambers are squeezed together which make the inside opening of the chambers close. This forces out all of the blood that is in the chambers. In order for the chambers to refill again, the heart muscles must be in diastole or relax in order to open the chamber back up. This makes space for more blood to come into the chambers. This is important because if diastole didn't occur, then there wouldn't be any blood to push out during the next systole.

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