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The mitral valve (), also known as the bicuspid valve or left atrioventricular valve, is one of the four
heart valve A heart valve is a Check valve, one-way valve that allows blood flow, blood to flow in one direction through the chambers of the heart. Four valves are usually present in a mammalian heart and together they determine the pathway of blood flow thro ...
s. It has two cusps or flaps and lies between the
left atrium The atrium (Latin ātrium, “entry hall”) is the upper chamber through which blood enters the Ventricle (heart), ventricles of the heart. There are two atria in the human heart – the left atrium receives blood from the pulmonary (lung) circula ...
and the
left ventricle A ventricle is one of two large chambers toward the bottom of the heart The heart is a muscle, muscular Organ (anatomy), organ in most animals, which pumps blood through the blood vessels of the circulatory system. The pumped blood carries ...
of the
heart The heart is a cardiac muscle, muscular Organ (biology), organ in most animals, which pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste ...

heart
. The heart valves are all
one-way valve check valve Image:Check Valve.svg, 140px, Check valve symbol on piping and instrumentation diagrams. The arrow shows the flow direction. A check valve, non-return valve, reflux valve, retention valve, foot valve, or one-way valve is a valve ...
s allowing blood flow in just one direction. The mitral valve and the
tricuspid valve The tricuspid valve, or right atrioventricular valve, is on the right dorsal side of the mammalian heart, at the superior portion of the right ventricle A ventricle is one of two large chambers toward the bottom of the heart The heart i ...
are known as the atrioventricular valves because they lie between the atria and the ventricles. In normal conditions, blood flows through an open mitral valve during
diastole Image:Heart diastole.png, upright=1.5, Heart performance during ventricular diastole: early diastole is a suction mechanism that draws blood 'down' from the left atrium (pink) and right atrium (blue) into each of the two ventricles. Then, in late ve ...
with contraction of the left atrium, and the mitral valve closes during
systole The systole ( ) is the part of the during which some chambers of the contract after refilling with blood. The term originates, via , from (''sustolē''), from (''sustéllein'' 'to contract'; from ''sun'' 'together' + ''stéllein'' 'to se ...
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 left ventricle than atrium. In abnormal conditions, blood may flow backward through the valve (
mitral regurgitation Mitral regurgitation (MR), also known as mitral insufficiency, or mitral incompetence is a form of valvular heart disease in which the mitral valve is insufficient and does not close properly when the heart pumps out blood. Section: Valvular Hear ...

mitral regurgitation
) or the mitral valve may be narrowed (
mitral stenosis Mitral stenosis is a valvular heart disease Valvular heart disease is any cardiovascular disease Cardiovascular disease (CVD) is a class of diseases that involve the heart The heart is a muscle, muscular Organ (anatomy), organ in mo ...

mitral stenosis
).
Rheumatic heart disease Valvular heart disease is any cardiovascular disease Cardiovascular disease (CVD) is a class of diseases that involve the heart The heart is a muscle, muscular Organ (anatomy), organ in most animals, which pumps blood through the blood ...
often affects the mitral valve; the valve may also
prolapse In medicine Medicine is the Art (skill), art, science, and Praxis (process) , practice of caring for a patient and managing the diagnosis, prognosis, Preventive medicine, prevention, therapy, treatment or Palliative care , palliation of their ...
with age and be affected by
infective endocarditis Infective endocarditis is an infection An infection is the invasion of an organism's body Tissue (biology), tissues by Pathogen, disease-causing agents, their multiplication, and the reaction of host (biology), host tissues to the infectious ag ...
. The mitral valve is named after the
mitre The Mitre Corporation (stylized as The MITRE Corporation and MITRE) is an American not-for-profit A nonprofit organization (NPO), also known as a non-business entity, not-for-profit organization, or nonprofit institution, is a legal entity org ...

mitre
of a
bishop A bishop is an ordained, consecrated, or appointed member of the Clergy#Christianity, Christian clergy who is generally entrusted with a position of authority and oversight. Within the Catholic, Eastern Orthodox, Oriental Orthodox, Moravian Chu ...

bishop
, which resembles its flaps.


Structure

The mitral valve is typically 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.


Chordae tendineae

The valve leaflets are prevented from prolapsing into the left atrium by the action of
chordae tendineae The chordae tendineae (tendinous cords), colloquially known as the heart strings, are tendon-resembling fibrous cords of connective tissue that connect the papillary muscles to the tricuspid valve and the mitral valve The mitral valve (), also ...
. The chordae tendineae are inelastic
tendon A tendon or sinew is a tough, high-tensile-strength band of dense fibrous connective tissue that connects muscle Skeletal muscles (commonly referred to as muscles) are organs An organ is a group of tissues with similar functions. Plant ...

tendon
s attached at one end to
papillary muscle The papillary muscles are muscles located in the ventricles of the heart. They attach to the cusps of the atrioventricular valves (also known as the mitral and tricuspid valves) via the chordae tendineae The chordae tendineae (tendinous cords ...
s 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 the thickest ones (strut chords) are attached further from the free margin. This disposition has important effects on systolic stress distribution physiology.


Annulus

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 cardiac cycle is the performance of the human heart The heart is a cardiac muscle, muscular Organ (biology), organ in most animals, which pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxy ...
. The annulus contracts and reduces its surface area during
systole The systole ( ) is the part of the during which some chambers of the contract after refilling with blood. The term originates, via , from (''sustolē''), from (''sustéllein'' 'to contract'; from ''sun'' 'together' + ''stéllein'' 'to se ...
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 Mitral regurgitation (MR), also known as mitral insufficiency, or mitral incompetence is a form of valvular heart disease in which the mitral valve is insufficient and does not close properly when the heart pumps out blood. Section: Valvular Hear ...

mitral regurgitation
. The normal diameter of the mitral annulus is , and the circumference is . Microscopically, there is no evidence of an annular structure anteriorly, where the mitral valve leaflet is contiguous with the posterior aortic root.


Function

During
left ventricular A ventricle is one of two large chambers toward the bottom of the heart The heart is a muscle, muscular Organ (anatomy), organ in most animals, which pumps blood through the blood vessels of the circulatory system. The pumped blood carries ...
diastole Image:Heart diastole.png, upright=1.5, Heart performance during ventricular diastole: early diastole is a suction mechanism that draws blood 'down' from the left atrium (pink) and right atrium (blue) into each of the two ventricles. Then, in late ve ...
, after the pressure drops in the left ventricle due to relaxation of the ventricular
myocardium Cardiac muscle (also called heart muscle or myocardium) is one of three types of vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular A multicellular organism is an organism ...

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 An echocardiography, echocardiogram, cardiac echo or simply an echo, is an ultrasound Ultrasound is s with higher than the upper audible limit of human . Ultrasound is not different from "normal" (audible) sound in its physical properties ...
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 left ventricle contributes about 20% to the volume in the left ventricle prior to ventricular systole and is known as the ''atrial kick''. The
mitral annulus The mitral valve (), also known as the bicuspid valve or left atrioventricular valve, is one of the four heart valve A heart valve is a Check valve, one-way valve that allows blood flow, blood to flow in one direction through the chambers of the he ...
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 A sphincter is a circular muscle Skeletal muscles (commonly referred to as muscles) are organs An organ is a group of tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A give ...
. 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. Leaking valves can be corrected by mitral valve annuloplasty, a common surgical procedure that aims at restoring proper leaflet adjustment.


Clinical significance


Disease

There are some
valvular heart disease Valvular heart disease is any cardiovascular disease Cardiovascular disease (CVD) is a class of diseases that involve the heart The heart is a muscle, muscular Organ (anatomy), organ in most animals, which pumps blood through the blood ...
s that affect the mitral valve.
Mitral stenosis Mitral stenosis is a valvular heart disease Valvular heart disease is any cardiovascular disease Cardiovascular disease (CVD) is a class of diseases that involve the heart The heart is a muscle, muscular Organ (anatomy), organ in mo ...

Mitral stenosis
is a narrowing of the valve. This can be heard as an opening snap; a heart sound which is not normally present. Classic
mitral valve prolapse Mitral valve prolapse (MVP) is a valvular heart disease Valvular heart disease is any cardiovascular disease Cardiovascular disease (CVD) is a class of diseases that involve the heart The heart is a muscle, muscular Organ (anatomy), ...
is caused by an excess of
connective tissue Connective tissue is one of the many basic types of animal Animals (also called Metazoa) are multicellular A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions ...
that thickens the spongiosa layer of the cusp and separates
collagen Collagen () is the main structural protein Proteins are large biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallography by Max Perutz and Sir John Cowder ...

collagen
bundles in the fibrosa. This weakens the cusps and adjacent tissue, resulting in an increased cuspal area and lengthening of the chordae tendineae. Elongation of the chordae tendineae often causes rupture, commonly to the chordae attached to the posterior cusp. Advanced lesions—also commonly involving the posterior leaflet—lead to leaflet folding, inversion, and displacement toward the left atrium. A valve prolapse can result in
mitral insufficiency Mitral regurgitation (MR), also known as mitral insufficiency, or mitral incompetence is a form of valvular heart disease in which the mitral valve does not close properly when the heart pumps out blood. Section: Valvular Heart Disease Rupture or ...
, which is the regurgitation or backflow of blood due to the incomplete closure of the valve.
Rheumatic heart disease Valvular heart disease is any cardiovascular disease Cardiovascular disease (CVD) is a class of diseases that involve the heart The heart is a muscle, muscular Organ (anatomy), organ in most animals, which pumps blood through the blood ...
often affects the mitral valve. The valve may also be affected by
infective endocarditis Infective endocarditis is an infection An infection is the invasion of an organism's body Tissue (biology), tissues by Pathogen, disease-causing agents, their multiplication, and the reaction of host (biology), host tissues to the infectious ag ...
Surgery can be performed to replace or repair a damaged valve. A less invasive method is that of mitral valvuloplasty which uses a balloon
catheter In medicine Medicine is the science Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity, awareness, or understanding of someone or something, such as facts ( descriptive knowledge) ...

catheter
to open up a stenotic valve. Rarely there can be a severe form known as caseous
calcification Calcification is the accumulation of calcium Calcium is a chemical element with the Symbol (chemistry), symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when expose ...
of the mitral valve that can be mistaken for intracardiac mass or thrombus.


Investigation

The closing of the mitral valve and the tricuspid valve constitutes the first heart sound (S1), which can be heard with a
stethoscope The stethoscope is an acoustic medical Medicine is the science and Praxis (process) , practice of caring for a patient, managing the diagnosis, prognosis, Preventive medicine, prevention, therapy, treatment, Palliative care , palliation o ...

stethoscope
. It is not the valve closure itself which produces the sound but the sudden cessation of blood flow, when the mitral and tricuspid valves close.. Abnormalities associated with the mitral valve can often be heard when
listening with a stethoscope
listening with a stethoscope
. The mitral valve is often also investigated using an
ultrasound scan Medical ultrasound includes diagnostic Diagnosis is the identification of the nature and cause of a certain phenomenon. Diagnosis is used in many different academic discipline, disciplines, with variations in the use of logic, analytics, and ...

ultrasound scan
, which can reveal the size and flow of blood through the valve.


Etymology

The word ''mitral'' comes from
Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman Republic, it became ...

Latin
, meaning "shaped like a
mitre The Mitre Corporation (stylized as The MITRE Corporation and MITRE) is an American not-for-profit A nonprofit organization (NPO), also known as a non-business entity, not-for-profit organization, or nonprofit institution, is a legal entity org ...

mitre
" (bishop's hat). The word ''bicuspid'' uses combining forms of ''
bi- Numeral or number prefixes are prefix A prefix is an which is placed before the of a word. Adding it to the beginning of one word changes it into another word. For example, when the prefix ''un-'' is added to the word ''happy'', it creates ...
'', from Latin, meaning "double", and ''
cusp Cusp may refer to: Mathematics *Cusp (singularity) In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and ...

cusp
'', meaning "point", reflecting the dual-flap shape of the valve.


Gallery

Image:Gray498.png, The human heart, viewed from the front. The mitral valve is visible on the right as the "bicuspid valve" Image:Gray1216.svg, The chest, showing surface relations of
bone A bone is a rigid tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Triphosa haesitata'', a species of geometer moth found in North America * ''Triphosa dubit ...

bone
s,
lungs The lungs are the primary organs of the respiratory system The respiratory system (also respiratory apparatus, ventilatory system) is a biological system consisting of specific organs and structures used for gas exchange in animal ...

lungs
(purple),
pleura The pulmonary pleurae (''sing.'' pleura) are the two opposing layers of serous membrane In anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology Biology is the natural science that studies life and living orga ...

pleura
(blue), and
heart The heart is a cardiac muscle, muscular Organ (biology), organ in most animals, which pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste ...

heart
(red).
Heart valves A heart valve is a one-way valve check valve Image:Check Valve.svg, 140px, Check valve symbol on piping and instrumentation diagrams. The arrow shows the flow direction. A check valve, non-return valve, reflux valve, retention valve, foot valv ...

Heart valves
are labeled with " B", " T", "", and " P". Image:Mitral valve.jpg, Mitral valve, viewed in a
cadaver A cadaver or corpse is a dead human body that is used by medical students A medical school is a tertiary educational institution, or part of such an institution, that teaches medicine, and awards a professional degree for physicians and surg ...

cadaver
specimen from within the left atrium.


References


External links

*  — "Valves of the heart"
Cardiac Valve Animations - Perioperative Interactive Education Group
nbsp;— Cardiac valve animations


Further reading

* Ingels Jr, Neil B and Karlsson, Matts. Mitral Valve Mechanics. Linköping University Electronic Press, 2016. .
Open access
{{Authority control Cardiac anatomy Heart valves