Mitral valve

Mitral valve
Mitral valve
Diagram of the human heart (cropped).svg
Anterior (frontal) view of the opened heart. White arrows indicate normal blood flow. (Mitral valve labeled at center right.)
Gray495.png
Base of ventricles exposed by removal of the atria. (Bicuspid (mitral) valve visible at bottom left.)
Latin valva atrioventricularis sinistra, valva mitralis
Gray's subject #138 534
MeSH Mitral+Valve

The mitral valve (also known as the bicuspid valve or left atrioventricular valve) is a dual-flap (bi- from the Latin, meaning double, and mitral- from the Latin, meaning shaped like a mitre) valve in the heart that lies between the left atrium (LA) and the left ventricle (LV). The mitral valve (not to be confused with the congenital bicuspid aortic valve) and the tricuspid valve are known collectively as the atrioventricular valves because they lie between the atria and the ventricles of the heart and control the flow of blood.

During diastole, a normally-functioning mitral valve opens as a result of increased pressure from the left atrium as it fills with blood (preloading). As atrial pressure increases above that of the left ventricle, the mitral valve opens. Opening facilitates the passive flow of blood into the left ventricle. Diastole ends with atrial contraction, which ejects the final 20% of blood that is transferred from the left atrium to the left ventricle. This amount of blood is known as end diastolic volume (EDV), and the mitral valve closes at the end of atrial contraction to prevent a reversal of blood flow.

Contents

Anatomy

Operative view of The Mitral valve with a chordal rupture "fail" of the anterior leaflet

The mitral valve is typically 4–6 cm² in area. It has two cusps, or leaflets, (the anteromedial leaflet and the posterolateral leaflet) that guard the opening. The opening is surrounded by a fibrous ring known as the mitral valve annulus. (The orientation of the two leaflets resemble a bishop's mitre, whence the valve receives its name.[1]) The anterior cusp protects approximately two-thirds of the valve (imagine a crescent moon within the circle, where the crescent represents the posterior cusp). Note that although the anterior leaflet takes up a larger part of the ring and rises higher, the posterior leaflet has a larger surface area. These valve leaflets are prevented from prolapsing into the left atrium by the action of tendons attached to the posterior surface of the valve, chordae tendineae.

The inelastic chordae tendineae are attached at one end to the papillary muscles and the other to the valve cusps. Papillary muscles are fingerlike projections from the wall of the left ventricle. Chordae tendineae from each muscle are attached to both leaflets of the mitral valve. Thus, when the left ventricle contracts, the intraventricular pressure 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 to flow 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 quite away from the free margin. This disposition has important effects on systolic stress distribution physiology [2](video).

Normal physiology

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 70-80% 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.

After the E wave, there is a period of slow filling of the ventricle.

Left atrial contraction (left atrial systole) (during left ventricular diastole) causes added blood to flow across the mitral valve immediately before left ventricular systole. This late flow across the open mitral valve is seen on doppler echocardiography of the mitral valve as the A wave. The late filling of the LV contributes about 20% to the volume in the left ventricle prior to ventricular systole, and is known as the atrial kick.

The mitral annulus changes in shape and size during the cardiac cycle. It is smaller at the end of atrial systole due to the contraction of the left atrium around it, like a sphincter. This reduction in annulus size at the end of atrial systole may be important for the proper coapting of the leaflets of the mitral valve when the left ventricle contracts and pumps blood.[3] Leaking valves can be corrected by mitral valve annuloplasty, a common surgical procedure that aims at restoring proper leaflet coaptation.

Surface anatomy

The closing of the mitral valve and the tricuspid valve constitutes the first heart sound (S1). It is not actually the valve closure which produces a sound but rather the sudden cessation of blood flow caused by the closure of the mitral and tricuspid valves. The mitral valve opening is normally not heard except in Mitral Stenosis (narrowing of the valve) as the Opening Snap. Flow of blood into the heart during rapid filling is not normally heard except in certain pathological states where it constitutes the third heart sound (S3).

Mitral valve

Additional images

See also

References

External links


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Look at other dictionaries:

  • mitral valve — n. the valve between the left atrium and left ventricle of the heart, preventing a flow of blood back into the atrium during systole …   English World dictionary

  • Mitral valve — One of the four valves of the heart, the mitral valve is situated between the left atrium and the left ventricle. It permits blood to flow one way: from the left atrium into the left ventricle The mitral valve has two flaps (cusps) and so is… …   Medical dictionary

  • Mitral valve prolapse — Mitral valve prolapses Classification and external resources In mitral valve prolapse, the leaflets of the mitral valve prolapse back into the left atrium. ICD 10 …   Wikipedia

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  • Mitral valve annuloplasty — is a surgical technique for the repair of leaking mitral valves. Due to various factors, the two leaflets normally involved in sealing the mitral valve to reterograde flow, may not coapt properly. Surgical repair typically involves the… …   Wikipedia

  • Mitral valve prolapse — Drooping down or abnormal bulging of the mitral valve’s cusps backward into the * * * mitral valve prolapse n a valvular heart disorder in which one or both mitral valve flaps close incompletely during systole usu. producing either a click or… …   Medical dictionary

  • mitral valve prolapse syndrome — prolapse of the mitral valve, often with regurgitation, associated with myxomatous proliferation of the leaflets of the mitral valve, a common, usually benign, often asymptomatic condition characterized by midsystolic clicks and late systolic… …   Medical dictionary

  • mitral valve prolapse — noun cardiopathy resulting from the mitral valve not regulating the flow of blood between the left atrium and left ventricle of the heart • Hypernyms: ↑valvular heart disease * * * noun : a valvular heart disorder in which one or both mitral… …   Useful english dictionary

  • mitral valve stenosis — noun obstruction or narrowing of the mitral valve (as by scarring from rheumatic fever) • Syn: ↑mitral stenosis • Hypernyms: ↑stenosis, ↑stricture, ↑valvular heart disease …   Useful english dictionary

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