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Introduction of Semilunar Valve

The heart is one of the most important organs of the human body and it is made up of complex and intricate parts that help in the proper and correct functioning of the organ. One of the most important parts of the heart would have to be the valves that are present. The human heart always consists of two atria and two ventricles. These four chambers play a very important role in blood circulation. The atria take blood from all the parts of the body with the help of superior vena cava and inferior vena cava. The blood is being pumped into the lungs from the ventricles. The heart has valves that control the movement of blood inside the body. The sounds are only produced when they open. 


The heart is about the size of a closed fist, that functions in a way as the body’s circulatory pump. It takes in deoxygenated blood through the veins and delivers it to the lungs for the oxygenation process. It then pumps it into the arteries which provide oxygen and nutrients to the body tissues by transporting the blood throughout the body. The heart is located in the thoracic cavity medial to the lungs, and is posterior to the sternum.


The Valves of the Heart

To prevent blood from flowing backwards back into the heart, a system of one-way valves are present in the heart. The heart valves can be broken down to two types: atrioventricular and semilunar valves.


Atrioventricular valves - The atrioventricular (AV) valves are located in the middle of the heart between the atria and ventricles and allow blood to flow from the atria into the ventricles. The valve on the right side of the heart is called the tricuspid valve. It is made of three cusps that separate to allow blood to pass through and connect to block the regurgitation of the blood. The AV valve located on the left side of the heart is called the bicuspid valve because it has two cusps.


Semilunar valves - The semilunar valves, for the crescent moon shape of their cusps, are located in a place between the ventricles and the arteries that carry blood away from the heart. The semilunar valve located on the right side of the heart is the pulmonary valve of blood. The semilunar valve located on the left side of the heart is the aorta. It prevents the aorta from regurgitating the blood back to the left ventricle. The semilunar valves are kind of  smaller than the AV valves.


These are the structures that ensure the proper and even flow of blood in the correct direction in the body of a human being. These valves are composed mainly of different connective tissues and also have another very important part known as the endocardium. The endocardium is an inner layer that is present in the heart. In this article, students are going to learn more about the semilunar valves.


The electrocardiogram is a non-invasive device that measures and monitors the electrical activity of the heart through the skin. The device produces a distinctive waveform in response to the electrical changes taking place within the heart. The sounds of a normal heartbeat are caused by the blood pushing on the valves of the heart. During a normal heartbeat, these sounds always repeat in a matter of regular pattern of lubb dupp pause. Any sound such as liquid rushing indicates a problem in the heart. The cause of these sounds are defects in the atrial or ventricular septum or leakage in the valves. 


Semilunar Valves of the Heart

We all know that valves of the heart have a very important function to play and that is to ensure even and proper blood flow into the heart and that too in one direction. Well, there are 4 types of valves and they are divided into 2 different groups known as the atrioventricular valves and the semilunar valves.


The atrioventricular valves are the ones that are composed of the mitral or the bicuspid valve and the tricuspid valve. These are located mostly in the corresponding ventricles and the atria, hence the name.


The Semilunar valves compose of the aortic valve and the pulmonary valve. These valves are located right between the ventricles as well as the artery that is corresponding to them. The main function of the pulmonary and the aortic Semilunar valve is to regulate the blood flow that leaves our heart.


Semilunar Valves Location

When it comes to the Semilunar valves of the heart, there are some details that students need to know about. For example, the location of these semilunar valves is right between the outflow vessels of the heart and the ventricles. The closing happens right at the beginning of the diastole or the ventricular relaxation. This is what makes the second sound of the heart. We will be going into some more detail about the Semilunar valves that will provide a deeper understanding of the topic to the students.


What are the 2 Semilunar Valves?

We all are familiar with the fact that there are 2 different types of valves that make up the semilunar valves. These valves are known as the pulmonary and the aortic Semilunar valves.


  • Pulmonary Semilunar Valves: 

One of the most important things to keep in mind about the pulmonary Semilunar valves is that these are situated right between the pulmonary trunk (also known as the pulmonary orifice) and the right ventricle of the heart. There are 3 different cusps that are a part of the pulmonary valve and these are the anterior, left, and right cusps. These cusps are named by the position that they tend to have in a fetus before the rotation of the heart takes place.


  • Aortic Semilunar valves: 

Another part of the Semilunar valves of the heart would have to be the aortic Semilunar valves. These are the valves that are situated right between the ascending aortas (or more commonly known as the aortic orifice) and the left ventricle of the heart. This particular valve also consists of 3 different cusps which are known as the posterior, left, and right cusps.


With the left as well as the right aortic tissue, the right and left coronary arteries are formed. During the recoiling of the blood that happens in the ventricular diastole, the blood is filled in the aortic sinuses and it can enter the coronary arteries from there so that it can be supplied to the myocardium. This is one of the main semilunar valves function examples that you need to know about. We are going to be talking more about it later.


The structure of the aortic and pulmonary Semilunar valves is pretty much the same. There are certain sides that are present in each of the valves and they are connected to the walls that are present in the outflow vessels. These vessels are dilated in order to form the particular sinus.


Semilunar Valves Function

Here we are going to discuss further the semilunar valve function. Well, these valves help in determining the correct direction and method of blood passage that happens between the main arteries and ventricles of the body. Hence, it also has a very important role to play in transporting the blood from the heart to other important organs of the body. These valves make sure that the blood flow is even and is transported without any difficulty. A proper understanding of the Semilunar valves can allow scientists and doctors to come up with several important clinical therapies that can help in the treatment process for certain degenerative and congenital diseases.

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FAQs on Semilunar Valve

1. What are the 2 Semilunar Valves?

We all know that there are 4 different valves that are present in the human heart. These are further divided into 2 categories known as the atrioventricular valves and the Semilunar valves. The Semilunar valves are further divided into 2 different types. These types are known as the pulmonary semilunar valve and the aortic semilunar valve. These valves are made up of certain connective tissues and these help in the regulation of the blood that is further pumped into all of the important organs of the human body. The structure of these valves are pretty much the same and they both consist of 3 different cusps each that further help give them the defining structure that they have.

2. Where are the Semilunar Valves Located?

There are 2 important valves that make up the entire semilunar valves section of the heart and these are known as the pulmonary and the aortic semilunar valve. One of the important things to know about the locations of these essential semilunar valves is that these are situated right in the middle of the outflow vessels that are present in the heart and the important ventricles. There is closing right in the starting of the diastole which is also known as ventricular relaxation. This act assists in the formation of the second sounds that the heart tends to make.

3. What is the function of a semilunar valve?

The function of a semilunar valve is to carry the blood to the distant parts of the body. It also prevents the flow of blood from the aorta and pulmonary artery to the ventricles of the heart. The pulmonary semilunar valve functions in a way that it opens as a result of ventricular contraction allowing the blood to flow towards the aorta and pulmonary arteries. When ventricles relax, the semilunar valves close because the pressure decreases to produce the second heart sound. 

4. What are the differences in semilunar valves between humans and other animals?

The shape and structure of semilunar valves of humans and other animals are slightly different. The muscles in the valves are lesser in humans, as compared to other animals. The aortic valve is wider in humans. The membranous septum between the aortic and mitral valve is not present when it comes to sheep. It differs in length in various species.

5. What is the Atrioventricular valve? How is it different from a semilunar valve?

The atrioventricular valves divide into the two atria and ventricles. They don’t let the backflow of blood from ventricles to atria. Semilunar valves separate arteries and prevent the backflow of blood from the arteries to ventricles. Semilunar valves are composed of cusps, atrioventricular valves are made of leaflets.  Semilunar valves are never attached to the walls of arteries, while atrioventricular valves are attached to the walls of ventricles.


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