Heart valve

From Wikipedia, the free encyclopedia

Illustration of the valves of the heart when the ventricles are relaxed. The tricuspid and mitral valves are open, while the pulmonary and aortic valves are closed. The chordae tendineae and papillary muscles are also shown.

A heart valve normally allows blood flow in only one direction through the heart. The four valves commonly represented in a mammalian heart determine the pathway of blood flow through the heart. A heart valve opens or closes incumbent upon differential blood pressure on each side.^[1]^[2]^[3]

The four valves in the heart are:^[4]

The two atrioventricular (AV) valves, which are between the atria and the ventricles, are the mitral valve (also called the bicuspid valve), and the tricuspid valve.
The two semilunar (SL) valves, which are in the arteries leaving the heart, are the aortic valve and the pulmonary valve.

A form of heart disease occurs when a valve malfunctions and allows some blood to flow in the wrong direction. This is called regurgitation.

Structure

Heart valves separate the atria from the ventricles, or the ventricles from a blood vessel. Heart valves are situated around a tendinous ring, and possess cusps. Each valve possesses three cusps, except for the mitral valve, which possesses only two.

Atrioventricular

This is further explanation of the echocardiogram above. MV: Mitral valve, TV: Tricuspid valve, AV: Aortic valve, Septum: Interventricular septum. Continuous lines demarcate septum and free wall seen in echocardiogram, dotted line is a suggestion of where the free wall of the right ventricle should be. The red line represents where the upper left loop in the echocardiogram transects the 3D-loop, the blue line represents the lower loop.

An artificial heart valve may be used to surgically replace a patient's damaged valve.

These are small valves that prevent backflow from the ventricles into the atrium during systole. They are anchored to the wall of the ventricle by chordae tendineae, which prevent the valve from inverting.

The chordae tendineae are attached to papillary muscles that cause tension to better hold the valve. Together, the papillary muscles and the chordae tendineae are known as the subvalvular apparatus. The function of the subvalvular apparatus is to keep the valves from prolapsing into the atria when they close. The subvalvular apparatus have no effect on the opening and closure of the valves, however. This is caused entirely by the pressure gradient across the valve. The peculiar insertion of chords on the leaflet free margin however provides systolic stress sharing between chords according to their different thickness.^[5]

The closure of the AV valves is heard as the first heart sound (S1).

Mitral valve

Main article: mitral valve

Also known as the "bicuspid valve" because it contains two flaps, the mitral valve gets its name from the resemblance to a bishop's mitre (a type of hat). It allows the blood to flow from the left atrium into the left ventricle. It is on the left side of the heart and has two cusps.

A common complication of rheumatic fever is thickening and stenosis of the mitral valve.

Tricuspid valve

Main article: tricuspid valve

The tricuspid valve is the three-flapped valve on the right side of the heart, between the right atrium and the right ventricle which stops the backflow of blood between the two. It has three cusps.

Semilunar

Wiggers diagram, showing various events during a cardiac cycle, with closures and openings of the aortic and mitral marked in the pressure curves.

These are located at the base of both the pulmonary trunk (pulmonary artery) and the aorta, the two arteries taking blood out of the ventricles. These valves permit blood to be forced into the arteries, but prevent backflow of blood from the arteries into the ventricles. These valves do not have chordae tendineae, and are more similar to valves in veins than atrioventricular valves. Closure of the semilunar valves causes the second heart sound.

Aortic valve

Main article: aortic valve

The aortic valve lies between the left ventricle and the aorta. The aortic valve has three cusps. During ventricular systole, pressure rises in the left ventricle. When the pressure in the left ventricle rises above the pressure in the aorta, the aortic valve opens, allowing blood to exit the left ventricle into the aorta. When ventricular systole ends, pressure in the left ventricle rapidly drops. When the pressure in the left ventricle decreases, the aortic pressure forces the aortic valve to close. The closure of the aortic valve contributes the A2 component of the second heart sound (S2).

The most common congenital abnormality of the heart is the bicuspid aortic valve. In this condition, instead of three cusps, the aortic valve has two cusps. This condition is often undiagnosed until the person develops calcific aortic stenosis.^[6]^[7] Aortic stenosis occurs in this condition usually in patients in their 40s or 50s, an average of over 10 years earlier than in people with normal aortic valves.

Pulmonary valve

Main article: pulmonary valve

The pulmonary valve (sometimes referred to as the pulmonic valve) is the semilunar valve of the heart that lies between the right ventricle and the pulmonary artery, and has three cusps. Similar to the aortic valve, the pulmonary valve opens in ventricular systole, when the pressure in the right ventricle rises above the pressure in the pulmonary artery. At the end of ventricular systole, when the pressure in the right ventricle falls rapidly, the pressure in the pulmonary artery will close the pulmonary valve.

The closure of the pulmonary valve contributes the P2 component of the second heart sound (S2). The right heart is a low-pressure system, so the P2 component of the second heart sound is usually softer than the A2 component of the second heart sound. However, it is physiologically normal in some young people to hear both components separated during inhalation.

Cusps

The cusps of the heart valves serve to seal the heart valves when closed. There are three cusps for each valve except for the mitral valve, which has only two (hence its alternate name, "bicuspid valve"). "Nodules" are located at the tip of the valve, to form a tighter seal.

The pulmonary valve has a left, right, and anterior cusp^[8]
The aortic valve has a left, right, and posterior cusp. ^[9]
The tricuspid valve has an anterior, posterior, and septal cusp.
The mitral valve only has two cusps, the anterior and posterior cusp.

Base of ventricles exposed by removal of the atria. (Valves visible on top of heart.)
Aorta laid open to show the semilunar valves. (Note that captions don't align with current terminology.)

Variation

Physiology

In general, motion of the heart valves is determined using the Navier-Stokes equation; using boundary conditions of the blood pressures, pericardial fluid, and external loading as the constraints.

Motion of the heart valves is used as a boundary condition in the Navier-Stokes equation in determining the fluid dynamics of blood ejection from the left and right ventricles into the aorta and the lung.

Relationship between pressure and flow in open valves

The pressure drop, ${\Delta }p$ , across an open heart valve relates to the flow rate, Q, through the valve:

$a{{\partial }Q \over {\partial }t}+bQ^{2}={\Delta }p$

If:

-Inflow energy conserved

-Stagnant region behind leaflets

-Outflow momentum conserved

-Flat velocity profile

Valves with a single degree of freedom

Usually the aortic and mitral valves are incorporated in valve studies within a single degree of freedom. These relationships are based on the idea of the valve being a structure with a single degree of freedom. These relationships are based upon the Euler equations.

Equations for the aortic valve in this case:

${\rho }\left({{\partial }u \over {\partial }t}+{u{\partial }u \over {\partial }x}\right)+{{\partial }p \over {\partial }x}=0$

${{\partial }A \over {\partial }t}+{{\partial } \over {\partial }x}(Au)=0$

$A(x,t)=A_{0}\left(1-[1-{\Lambda }(t)]{x \over {L}}\right)^{2}$

$\int _{{0}}^{{L}}p(x,t){{\partial }A \over {\partial }x}\,dx=[A_{0}-A(L,t)]p(L,t)$

where:

u=axial velocity

p=pressure

A=cross sectional area of valve

L=axial length of valve

${\Lambda }$ (t)=single degree of freedom; when ${\Lambda }^{2}(t)={A(L,t) \over {A_{0}}}$

Atrioventricular valve

Clinical relevance

GIF-animation of a moving echocardiogram; a 3D - loop of a heart viewed from the apex (top), showing the apical part of the ventricles removed and the mitral valve clearly visible. Due to missing data the leaflets of the tricuspid and aortic valves are not clearly visible, but the openings are; the pulmonary valve is not visible. On the left are two standard 2D views (taken from the 3D dataset) showing tricuspid and mitral valves (above) and aortal valve (below).

Stenosis

Regurgitation

Infective endocarditis

Notes

↑ "Heart Valves". Heart and Stroke Encyclopedia. American Heart Association, Inc. Retrieved 2010-08-05.
↑ Klabunde, RE (2009-07-02). "Pressure Gradients". Cardiovascular Physiology Concepts. Richard E. Klabunde. Retrieved 2010-08-06.
↑ Klabunde, RE (2007-04-05). "Cardiac Valve Disease". Cardiovascular Physiology Concepts. Richard E. Klabunde. Retrieved 2010-08-06.
↑ not counting the valve of the coronary sinus, and the valve of the inferior vena cava
↑ J Cardiovasc Surg (Turin) 2000 Apr;41(2):193-202 video
↑ Bertazzo, S. et al. Nano-analytical electron microscopy reveals fundamental insights into human cardiovascular tissue calcification. Nature Materials 12, 576-583 (2013).
↑ Miller, J. D. Cardiovascular calcification: Orbicular origins. Nature Materials 12, 476-478 (2013).
↑ 20:21-0102 at the SUNY Downstate Medical Center - "Heart: The Pulmonic Valve"
↑ 20:29-0104 at the SUNY Downstate Medical Center - "Heart: The Aortic Valve and Aortic Sinuses"

Additional images

Illustration of heart valves (superior view)
Illustration of the valves of the heart when the ventricles are contracting.

External links

Anatomy of torso, cardiovascular system: heart (TA A12.1, TH H3.09.01, GA 5.524)

General

Surface

Internal

atria interatrial septum musculi pectinati sulcus terminalis ventricles interventricular septum trabeculae carneae chordae tendineae papillary muscle valves cusps atrioventricular septum

cardiac skeleton

intervenous tubercle

Chambers

Right heart	(venae cavae, coronary sinus) → right atrium (atrial appendage, fossa ovalis, limbus of fossa ovalis, crista terminalis, valve of inferior vena cava, valve of coronary sinus) → tricuspid valve → right ventricle (conus arteriosus, moderator band/septomarginal trabecula) → pulmonary valve → (pulmonary artery and pulmonary circulation)

Left heart	(pulmonary veins) → left atrium (atrial appendage) → mitral valve → left ventricle → aortic valve (aortic sinus) → (aorta and systemic circulation)

Layers

Endocardium	heart valves

Myocardium	conduction system: cardiac pacemaker SA node AV node bundle of His Purkinje fibers

Pericardial cavity	pericardial sinus

Pericardium	fibrous pericardium sternopericardiac ligaments serous pericardium epicardium/visceral layer fold of left vena cava

M: HRT

anat/phys/devp

noco/cong/tumr, sysi/epon, injr

proc, drug (C1A/1B/1C/1D), blte

This article is issued from Wikipedia. The text is available under the Creative Commons Attribution/Share Alike; additional terms may apply for the media files.