What are the semilunar valves?
There are four heart valves that regulate blood in the human body. They act as doorways between the heart’s lower chambers and upper chambers, which are the atria and the ventricles.
Two of the valves control blood coming into the heart and two of them pump blood out. The valves that pump blood out are known as the semilunar valves. The aortic valve is the left semilunar. The pulmonary valve is the right semilunar.
Because the leaflets (cusps) of the pulmonary and aortic valves take the shape of half-moons, the valves are said to be “semilunar.”
What do the semilunar valves look like?
The semilunar valves are malleable, pocket-like structures that are made up of reinforced connective tissue and are covered by endocardium. This prevents inversion of the heart valves.
The aortic valve lies between the left ventricle and the heart’s aorta. The pulmonary valve separates the pulmonary artery and the right ventricle. Each of the valves is supported by a fibrous annulus or ring of tissue and features cusps that meet tightly (coapt) when the valves close.
Both the aortic valve and the pulmonary valve have three leaflets. Unlike the atrioventricular valves, though, they do not have chordae tendineae that attach to papillary muscles. Instead, they open and close due to blood pressure within the heart between the atria and the ventricles.
What are the functions of the semilunar valves? How do they function?
The semilunar valves facilitate blood flow from the ventricles to the aortic and pulmonary arteries when the valves open and prevent blood from regurgitating into the ventricles when they close.
The aortic valve regulates blood that enters the aorta from the left ventricle, while the pulmonary valve regulates blood entering the pulmonary artery from the right ventricle. Both valves open and close according to pressure differences between the heart’s atria and ventricles.
When the ventricles relax, atrial pressure increases, forcing open the atrioventricular valves and allowing blood into the ventricles. When the ventricles contract, ventricular pressure increases, causing the AV valves to shut and the semilunar valves to open, which allows blood to pass through.