Mitral valve
Mitral valve (Left Atrioventricular Valve)
The mitral valve, named for its resemblance to a bishop’s miter, sits between the left atrium and left ventricle. This valve’s function is to prevent the back flow of blood during the ventricle’s contraction phase, thus ensuring a unidirectional flow vital for efficient cardiac output.
Left atrioventricular orifice
The mitral valve guards the left atrioventricular orifice. Smaller than its right-sided counterpart, the right atrioventricular orifice, this orifice serves as the critical portal through which blood transitions from the left atrium to the left ventricle.
The mitral valve is also named the bicuspid, and it has this name because it has two proeminent leaflets (cusps) – The anterior leaflet and the posterior leaflet.
Anterior leaflet of left atrioventricular valve
The larger and more prominent leaflet of the mitral valve is the anterior leaflet. It is strategically positioned between the left atrioventricular orifice and aortic orifice. It functions as a shield, coordinating closely with the heart’s rhythmic contractions to regulate blood flow.
Posterior leaflet of left atrioventricular valve
Smaller and situated posteriorly, it complements the anterior leaflet, ensuring that the valve’s closure is secure and complete.
Commissural leaflets
At the junction, the anterior leaflet of mitral valve and posterior leaflet of mitral valve are continuous at the commissures. When the valve closes, this continuity becomes more pronounced, and the commissural leaflets of mitral valve become visible. These leaflets facilitate the seamless operation of the valve.
Relationship to cardiac cycle
Similar to the tricuspid valve, the mitral valve opens during ventricular diastole to allow blood from the left atrium into the ventricle, and closes during ventricular systole to prevent backflow into the left atrium.
Left Fibrous Ring
The Mitral valve as the tricuspid valve is surrounded by the left fibrous ring, or annulus. This ring provides the architectural framework that maintains the mitral valve’s shape and integrity. It anchors the leaflets and ensures their correct alignment.
Chordae Tendineae of mitral valve
Similar to the tricuspid valve, the mitral valve is tethered to the tips of the superior papillary muscle and inferior papillary muscle via tendinous cords, known as chordae tendineae, that anchor the posterior leaflet and the anterior leaflet of the mitral valve. Their primary role is to prevent the leaflets from inverting under the pressure of ventricular contraction. These cords are systematically organized, with some attaching directly to the leaflets’ free edges and others to their ventricular surface. This strategic arrangement enables the valve to withstand the intense pressures of ventricular systole (1).
Relationship to the Cardiac Cycle
During ventricular systole, the phase of the cardiac cycle when the ventricular muscle contracts, the mitral valve closes firmly. This action is crucial as it prevents the backflow of blood into the left atrium, ensuring that the blood is efficiently propelled forward into the systemic circulation.
In contrast, during ventricular diastole, the relaxation phase of the ventricle, the mitral valve opens to allow blood to flow freely from the left atrium into the left ventricle. This opening is essential for the heart to fill with blood, preparing it for the next contraction phase.