The mitral valve is one of a total of 4 heart valves. It separates the left atrium from the left ventricle. As a leaflet valve, the mitral valve consists of an anterior leaflet and a posterior leaflet. It prevents the backflow of blood from the left ventricle into the left atrium during systolic contraction of the ventricle. During diastole (relaxation) of the left ventricle, the mitral valve is open, allowing oxygenated blood to flow in from the left atrium and pulmonary vein.
What is the mitral valve?
The mitral valve, also called the bicuspid valve, separates the left atrium of the heart from the left ventricle (chamber). Like the tricuspid valve, which separates the right atrium from the right ventricle, it is designed as a so-called leaflet valve with an anterior leaflet (cuspis anterior) and a posterior leaflet (cuspis posterior). The mitral valve prevents blood from the right atrium from flowing back into the left atrium and pulmonary vein during systole (contraction). During diastole (relaxation) of the right ventricle, the mitral valve opens and oxygen-rich blood from the lungs, which has accumulated in the left atrium, flows into the main ventricle. In the subsequent systolic phase, the oxygen-rich blood is pumped through the aortic valve into the great circulation (systemic circulation). While minor leakage of the mitral valve is tolerated by the heart muscle, major leakage leads to sensitive limitations in cardiac output (mitral regurgitation I to IV).
Anatomy and structure
The mitral valve is formed from two thin connective tissue leaflets (leaflets), the anterior leaflet (cuspis anterior) and the posterior leaflet (cuspis posterior). Both sails arise from the connective tissue-like reinforcing ring that lines the opening between the left atrium and left ventricle. When open during diastole, both leaflets project into the left ventricle. When pressure builds up in the chamber (systole), the two leaflets fold back, resting against each other and closing the opening between the left atrium and left ventricle. To prevent the leaflets from folding over into the atrium, the edges of the leaflets are connected by fine chordae tendineae. The chordae tendineae arise from the papillary muscles, small outpouchings of the ventricular muscles that contract synchronously with the ventricular muscles. During systolic contraction of the ventricle, the papillary muscles also contract, thereby tightening the tendon filaments. They prevent the leaflets from inverting into the left atrium, which could no longer prevent blood reflux into the left atrium and pulmonary vein.
Function and Tasks
The main function of the mitral valve is to allow oxygen-rich blood that has accumulated in the left atrium to flow into the ventricle during the diastolic relaxation phase of the ventricle. During the subsequent systolic contraction of the ventricle, the mitral valve must prevent blood from flowing back into the atrium so that blood can be properly pumped through the aortic valve into the systemic circulation (great circulation). The mitral valve could also be called a passive flutter valve, which automatically responds to pressure differences upstream and downstream of the valve. The small mass of the two connective tissue lobes that make up the mitral valve makes the valve extremely responsive, so that when there is only a slight increase in pressure in the chamber, the valve closes almost without distortion. However, the light and thin “material” of the two leaflets would not withstand the pressure when closed and would turn over into the atrium with the effect of blood backflow. To prevent this from happening, the edges of the leaflets are stabilized by fine chordae, which allow the mitral valve to open toward the ventricle, but not to turn over into the atrium. To some extent, the tendon filaments actually respond actively because they arise from the papillary muscles, small protrusions of the ventricular muscles that contract in synchrony with the ventricular muscle culture. The process is somewhat comparable to the active seatbelt tensioning principle of a passenger car, in which the seatbelts are pulled tightly against the body in certain situations that suggest an impending impact.
Diseases
Mitral valve regurgitation and mitral stenosis are the two main conditions and diseases associated with reduced mitral valve function.Mitral valve insufficiency can have various causes and is designated as mitral valve insufficiency I, II, III or IV, depending on the functional impairment, with severity I signifying mild insufficiency and severity IV the most severe insufficiency. Common to all degrees of severity is that the mitral valve no longer closes properly, resulting in partial blood return to the left atrium. The insufficiency may be caused, for example, by tearing or shortening of the tendon sutures that hold the edge of the two leaflets, or by a hole in one of the two leaflets, or by overstretching of the tissue. Some forms of mitral stenosis, which results in decreased blood flow from the left atrium to the left ventricle, are congenital malformations and maldevelopments. For example, if additional membranous connective tissue has formed above the mitral valve in the constriction located there and obstructs blood flow, this is known as supravalvular mitral stenosis. In other forms of mitral stenosis, there is thickening of the valve leaflets, shortening of the chordae and direct adhesions of the leaflet edges to the papillary muscles. The valve leaflets become severely restricted in their mobility, and leakage and partial reflux of blood occur during systolic contraction of the ventricle. In rare cases, mitral valve atresia is found, which means complete closure, or the mitral valve was not created during embryonic development. In this case, it is part of the hypoplastic left heart syndrome.
Typical and common heart diseases
- Heart attack
- Pericarditis
- Heart failure
- Atrial fibrillation
- Heart muscle inflammation
