While the heart is responsible for maintaining blood circulation with its pumping action, four heart valves ensure that blood always flows in the same direction. The two semilunar valves are each located in the initial region of the large arterial outflow vessels of the two ventricles. The pulmonary valve serves as the outlet valve of the right chamber to feed the pulmonary circulation, and the aortic valve is the outlet valve of the left chamber to fill the systemic circulation.
What is the pocket valve?
A total of four heart valves ensure that the blood in the pulmonary and systemic circulation always has the same direction. The two heart valves that direct blood flow from the atria to the ventricles are designed as so-called leaflet valves. They serve as outlet valves for the atria and simultaneously as inlet valves for the ventricles. Both leaflet valves are closed during the tension and contraction phase (systole), while the two pocket valves, the pulmonary valve (valva trunci pulmonalis) in the right ventricle and the aortic valve (valvae aortae) in the left ventricle open during systole. To prevent blood from the arterial pressure vessels from flowing back into the ventricles, they close during the subsequent relaxation phase of the ventricles (diastole). The closure of the pocket valves maintains a residual diastolic pressure in the arterial vessels. This is the lower value of blood pressure. In contrast to the two leaflet valves, which differ somewhat anatomically because they are equipped with 2, and 3 leaflets, respectively, the two pocket valves are largely identical in design.
Anatomy and structure
The attachments of the two pocket flaps occur as early as the 5th to 7th week of gestation. The three crescent-shaped pockets of each valve develop from the intima, the innermost layer of the arterial outlets in both ventricles. At the end of each pocket is a small nodule (nodulus valvulae semilunaris) embedded in a valve leaflet. The nodules serve to support valve function. At the entrance of the short arterial pulmonary trunk in the right ventricle, the truncus pulmonalis, the right leaflet (valvula semilunaris dextra), the left leaflet (valvula semilunaris sinistra), and the anterior leaflet (valvula semilunaris anterior) develop. The aortic valve, located at the entrance of the aorta in the left ventricle, is also the two right and left semilunar leaflets and the leaflet located toward the ventricular septum (valvula semilunaris septalis). Since the two arterial branches of the coronary arteries are located directly in the indentation of the left and right pocket of the aortic valve, respectively, they are called right coronary, left coronary, and acoronary pocket (without coronary branch) in German usage. Both pocket valves are basically identical in construction, but the aortic valve is designed to be more robust than the pulmonary valve due to its higher stress. Occasionally, the aortic valve is formed of only two leaflets, which can be attributed to a genetically determined anomaly of the valve anatomy, without necessarily resulting in a serious functional defect. However, the risk that this will result in stenosis, a narrowing of the valve cross-section, later in life is significantly higher than with a normally formed valve.
Function and Tasks
The main roles and functions of the pocket valves are to prevent backflow of blood into the ventricles during diastole and to maintain diastolic blood pressure in the arterial vasculature of the systemic and pulmonary circulation. Both functions require that during the systolic phase of the ventricles, the pocket valves release a sufficiently large cross-sectional area to fill the arterial vasculature with the intended amount of blood and that the systolic blood pressure can be correctly adjusted. If the pocket valves are narrowed, this is called stenosis, and if they are not closed properly during the diastolic phase, this is called insufficiency. Insufficiency can be divided into different classes depending on its severity.Proper functionality of the leaflet valves in conjunction with proper functionality of the two leaflet valves, each separating the atria from the ventricles, is one of several prerequisites for normal cardiac performance and for preventing cardiac muscle thickening (hypertrophic cardiomyopathy) because of constant excessive demands due to existing stenoses or insufficiencies.
Diseases
Basically, stenoses or insufficiencies or combinations of both defects can occur in all 4 heart valves. In the case of stenosis, the heart valves release an insufficiently large cross-sectional area for blood flow, requiring the heart to pump at a higher rate to compensate. In valvular insufficiency, the corresponding heart valve no longer closes properly, so that in the case of the pocket valves, blood flows back into the ventricles from the aorta or from the trunk of the pulmonary arteries during diastole. This is also sufficient cause for the ventricles to respond with increased pumping, which in the long run can lead to hypertrophy of the myocardium, as in the case of stenosis. Stenosis or insufficiency of the pocket valves may be acquired by disease or may exist as congenital valvular defects from birth and be caused by genetic defects. Aortic valve stenosis is relatively common and accounts for about 43 percent of all valvular heart defects in Europe. Stenosis may result from inflammatory processes or it may be due to calcification of the three pockets. Reasons for the development of aortic valve insufficiency are mostly inflammatory processes, in the course of which there is a partial degradation of the pocket valves or which causes a widening of the aortic valve leaflet. Pulmonary valve defects are extremely rare. The most frequent cause of a stenosis at the pulmonary valve with a corresponding narrowing is genetic factors, which usually carry other more or less serious heart defects from birth. Insufficiency of the pulmonary valve is also relatively rare. Leakage of the pulmonary valve may develop gradually in pulmonary hypertension or in dilatation or outpouching of one of the pulmonary arteries.
