Mitral valve

The mitral valve (/ˈmaɪtrəl/), also known as the bicuspid valve or left atrioventricular valve, is a valve with two flaps in the heart, that lies between the left atrium and the left ventricle. The mitral valve and the tricuspid valve are known collectively as the atrioventricular valves because they lie between the atria and the ventricles of the heart.The human heart, viewed from the front. The mitral valve is visible on the right as the 'bicuspid valve'The chest, showing surface relations of bones, lungs (purple), pleura (blue), and heart (red). Heart valves are labeled with 'B', 'T', 'A', and 'P'.Mitral valve, viewed in a cadaver specimen from within the left atrium. The mitral valve (/ˈmaɪtrəl/), also known as the bicuspid valve or left atrioventricular valve, is a valve with two flaps in the heart, that lies between the left atrium and the left ventricle. The mitral valve and the tricuspid valve are known collectively as the atrioventricular valves because they lie between the atria and the ventricles of the heart. In normal conditions, blood flows through an open mitral valve during diastole with contraction of the left atrium, and the mitral valve closes during systole with contraction of the left ventricle. The valve opens and closes because of pressure differences, opening when there is greater pressure in the left atrium than ventricle, and closing when there is greater pressure in the ventricle than atrium. In abnormal conditions, blood may flow backwards through the valve (mitral regurgitation) or the mitral valve may be narrowed (mitral stenosis). Rheumatic heart disease often affects the mitral valve; the valve may also prolapse with age, and be affected by infective endocarditis. The mitral valve is named after the mitre of a bishop, which resembles its flaps. The mitral valve is typically 4 to 6 square centimetres (0.62 to 0.93 sq in) in area and sits in the left heart between the left atrium and the left ventricle. It has two leaflets (or 'cusps'), an anteromedial leaflet, and a posterolateral leaflet. The opening of the mitral valve is surrounded by a fibrous ring known as the mitral annulus. The anterior cusp covers approximately two-thirds of the valve (imagine a crescent moon within the circle, where the crescent represents the posterior cusp). Although the anterior leaflet takes up a larger part of the ring and rises higher, the posterior leaflet has a larger surface area. The valve leaflets are prevented from prolapsing into the left atrium by the action of chordae tendineae. The chordae tendineae are inelastic tendons attached at one end to papillary muscles in the left ventricle, and at the other to the valve cusps. Papillary muscles are finger-like projections from the wall of the left ventricle. When the left ventricle contracts, the pressure in the ventricle forces the valve to close, while the tendons keep the leaflets coapting together and prevent the valve from opening in the wrong direction (thus preventing blood flowing back to the left atrium). Each chord has a different thickness. The thinnest ones are attached to the free leaflet margin, whereas thickest ones (strut chords) are attached further from the free margin. This disposition has important effects on systolic stress distribution physiology. The mitral annulus is a fibrous ring that is attached to the mitral valve leaflets. Unlike prosthetic valves, it is not continuous. The mitral annulus is saddle shaped and changes in shape throughout the cardiac cycle. The annulus contracts and reduces its surface area during systole to help provide complete closure of the leaflets. Expansion of the annulus can result in leaflets that do not join soundly together, leading to functional mitral regurgitation. The normal diameter of the mitral annulus is 2.7 to 3.5 centimetres (1.1 to 1.4 in), and the circumference is 8 to 9 centimetres (3.1 to 3.5 in). Microscopically, there is no evidence of an annular structure anteriorly, where the mitral valve leaflet is contiguous with the posterior aortic root. During left ventricular diastole, after the pressure drops in the left ventricle due to relaxation of the ventricular myocardium, the mitral valve opens, and blood travels from the left atrium to the left ventricle. About 70 to 80% of the blood that travels across the mitral valve occurs during the early filling phase of the left ventricle. This early filling phase is due to active relaxation of the ventricular myocardium, causing a pressure gradient that allows a rapid flow of blood from the left atrium, across the mitral valve. This early filling across the mitral valve is seen on doppler echocardiography of the mitral valve as the E wave.