Aortic Semilunar Valve: Definition & Function

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  • 0:01 What Is the Aortic…
  • 0:43 How Does the Heart Work?
  • 2:02 Function of the Aortic…
  • 3:17 Problems with Aortic…
  • 4:30 Lesson Summary
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Lesson Transcript
Instructor: Amanda Robb

Amanda holds a Masters in Science from Tufts Medical School in Cellular and Molecular Physiology. She has taught high school Biology and Physics for 8 years.

This lesson is about the aortic semilunar valve in the heart. We'll explain what the semilunar valve is, how it keeps us alive, and what happens to people with a defective semilunar valve.

What Is the Aortic Semilunar Valve?

What keeps your body moving? How do you stay alive during exercise, even though you're asking your body to do so much? The answer is the amazing organ called your heart! The heart pumps blood throughout the body to deliver the oxygen and nutrients needed to make energy. Your body has to have the energy to keep moving! The heart has different sections, or chambers. These chambers must be separated so that blood can flow in a specific pattern. Small doors in between the chambers, called valves, do this job. A specific valve that allows blood to flow from the heart to the body is called the aortic semilunar valve. Here we see the heart with the aortic semilunar valve boxed in red.

How Does the Heart Work?

To learn more about the semilunar valve, let's take a look at how blood flows through the heart. Blood enters the heart through the inferior and superior vena cava. These vessels bring blood that has been used by the body back to the heart so that it can get more oxygen. The blood flows into the right atrium, the first chamber of the heart. The blood collects there until the tricuspid valve opens, allowing it to flow to a larger chamber called the right ventricle. After all the blood enters the ventricle, the tricuspid valve slams shut, preventing blood from flowing back into the right atrium. This is very important because it causes blood to flow in only one direction through the heart and blood vessels.

The right ventricle pumps the blood to the lungs through another valve, called the pulmonary semilunar valve, and then it returns to the left atrium. The blood flows through the bicuspid valve into the left ventricle. Again, when all the blood is in the left ventricle, the bicuspid valve slams shut to prevent blood from flowing backwards.

Next, the left ventricle pumps blood through the aortic semilunar valve into the aorta. The aorta is the largest blood vessel in your body and carries blood with oxygen from the heart to the body. The semilunar valve prevents blood from flowing back into the left ventricle and keeps it moving towards the body. Here is a diagram of blood flow through the heart.

Bloodflow Image

Function of the Aortic Semilunar Valve

All valves function to prevent blood backflow into the heart, acting like doors between the chambers. Imagine if you had a tube of toothpaste. The bottom end is sealed, right? This is analogous to the valve in the heart. It seals one chamber from another. Then imagine you squeeze the toothpaste. The toothpaste only comes out the cap end, right? Right! But, if we cut the seal off of the bottom and squeezed; toothpaste would seep from both ends, and we would have a mess!

The same thing happens with the valves. If the valve didn't shut once the blood enters the next chamber, as the chamber squeezed, or contracted, to pump the blood, the blood would go in both directions. This would push the blood backwards. It's very important that blood flows only one way, so we can keep fresh blood with oxygen going towards the body, and blood with no oxygen coming back to the heart to get more oxygen. Let's look at this diagram of blood flowing backwards through the heart, which happens if there is a problem with the aortic semilunar valve.

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