There are four different valves present in the heart. These are –
- Mitral valve
- Tricuspid valve
- Aortic valve
- Pulmonary valve
The mitral valve lies between the left atrium and left ventricle. The tricuspid valve lies between the right atrium and the right ventricle.
The aortic valve lies at the origin of the aorta and the pulmonary valve lies at the origin of the pulmonary artery.
Each of these valves serve to allow blood to flow in one direction alone. However, in certain clinical conditions, the heart valve function may be affected causing it to either become too narrow or start to leak.
A narrowed heart valve is called a ‘stenosed’ valve while a leaking heart valve is called a ‘regurgitant’ valve.
Structure of the heart valves
Each of the heart valves is made of strong connective tissue which appear as flaps. There may be multiple flaps in a valve and each of these are called leaflets. For example, the mitral valve has two leaflets while the tricuspid valve has three leaflets.
Surrounding each of these leaflets is a strong ring of fibrous tissue called the annulus. One edge of each leaflet is attached to the annulus and the other end is called the free edge. The role of the annulus is to maintain the shape of the valve and its integrity.
In the case of the mitral and the tricuspid valve, each of these valves is connected indirectly to the heart muscle through a network of fibrous strands called chordae tendinae. These chordae are in turn attached to a small muscular outgrowths from the wall of the ventricle called the papillary muscles. Together, the valve, annulus, chordae tendinae and papillary muscles are called the valvular apparatus.
Working of the heart valves
As the heart valves allow for blood flow from one chamber to the other, there has to be a particular pressure at which they either open or close.
Let us take the right atrium for example. The right atrium and the right ventricle are separated by the tricuspid valve. When the blood reaches the right atrium through the superior and inferior vena cava, the right atrium is gradually filled up with blood. This blood is prevented from passing into the right ventricle during the early stages of filling by the tricuspid valve.
However, when the pressure within the right atrium is sufficiently elevated, the tricuspid valve opens up and allows blood to flow down through the valve into the right ventricle. Once the pressure in the right ventricle is sufficiently highly, the valve closes and prevents any more blood from reaching the ventricle from the right atrium.
Similarly, the left ventricle when sufficiently full pumps blood into the aorta through the aortic valve. While the left ventricle is being filled by blood from the left atrium, the pressure in the left ventricle builds up.
When the left ventricle contracts, it exerts sufficient amount of pressure on the aortic valve that allows blood to flow into the aorta. When the pressure in the aorta exceeds that of the left ventricle sufficiently, the aortic valve closes and prevents any blood from coming back into the left ventricle from the aorta.
During the normal cardiac cycle, both the atria (right and left) get filled up at the same time. Once the pressures within the atrium are sufficiently high, the top part of the heart contracts and blood is pushed through the valves into the ventricles.
Once the ventricles have sufficient amount of blood within them, these valves close. The ventricles then contract and the pulmonary and aortic valves open up allowing blood to flow up the respective blood vessels. Once the ventricles are emptied, the valves close.
This pattern of contraction and blood flow occurs constantly on a regular basis.