Tricuspid and mitral valves
The tricuspid and mitral valves are called atrioventricular, since they are located between the atria and ventricles in the right and left halves of the heart. They consist of a dense connective tissue and are covered with endocardium - a thin layer lining the inner surface of the heart. The upper surface of the valves is smooth, and on the lower there are connective tissue chords that serve to attach the leaflets. The tricuspid valve has three valves, and the mitral valve has two valves (it is also called bivalve). The mitral valve got its name because of the similarity in form with the bishop's miter.
Pulmonary artery valve
The pulmonary artery valve is located at the exit point of the pulmonary trunk from the right ventricle. The pulmonary trunk carries blood from the heart to the lungs. Directly above the valve flaps of the pulmonary artery are small cavities filled with blood and preventing the adherence of the valves to the wall of the pulmonary trunk when the valve is opened. During the systole of the atria, blood flows through the open tricuspid and mitral valves into the ventricles. During the systole of the ventricles, a sudden increase in pressure leads to the closure of the atrioventricular valves. This prevents the return of blood to the atria. Valve flaps are held by chords, which do not allow them to open due to pressure in the ventricles. After the closure of the atrioventricular valves, blood flows through the semilunar valves into the pulmonary trunk and the aorta. Semilunar valves open due to high pressure in the ventricles and collapse as soon as the systole ends and the diastole begins.
Heart Activity
Using a phonendoscope, you can hear that every heartbeat is accompanied by the appearance of two heart tones. The first tone appears at the time of closure of the atrioventricular valves, and the second - at the moment of closing the valve of the pulmonary artery of the aortic valve. The chords move away from the edges and the lower surface of the valves of the tricuspid and mitral valves, and then they are directed downward and attached to the papillary muscles that protrude into the ventricular cavity.
Principle of operation of chords
Chords prevent the inverting of the valves of the atrioventricular valves into the atrial cavity under the action of high blood pressure during ventricular systole. They are attached to the adjacent valves, which ensures their tight closure during ventricular systole and prevents the flow of blood back to the atrium. The aortic valve and the pulmonary artery valve are also called semilunar. They are located on the way out of the blood from the heart and prevent the return of blood to the ventricles during diastole. Each of these two valves consists of half-moon shaped leaves, similar to pockets. They consist of connective tissue and are covered with endothelium. Endothelium makes the valves smooth.