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Valves of the Heart
Just as a car engine valve controls highly pressurized gaseous particles through cylinders;
similarly the heart valves control the flow of blood by opening and closing due pressure
changes in various chambers of the heart resulting from contraction and relaxation.
An average human heart pumps about 5 liters of blood per minute and approximately
7500 liters per day by continuously beating for 1,00,000 times. During an average
lifetime of 65 years the heart valve operates for approximately 2.5 billion times.
Physiologically, heart valves function is not just to maintain unidirectional flow but it’s
designed such that the blood elements which pass through it are not damaged and
excessive mechanical pressure operates on the cusps or leaflets without causing
thromboembolism.
Anatomically, the heart valves are flap like structures made up of endocardium and
connective tissue, which are meant for maintaining unidirectional flow of blood and
preventing the back flow of blood (regurgitation).
The heart has two kinds of valves, atrioventricular and semilunar valves.
 Semilunar valves include two valves similar in structure viz; aortic and
pulmonary.
 Atrioventricular valves include the tricuspid and mitral valve.
Semilunar valves located at base of pulmonary arteries and aorta have thin flaps of
muscular tissue, known as leaflets or cusps, which allow blood to let in easily due to
ventricular systolic pressure and close to prevent backward flow by a minimal reverse
flow due diastole. These lack chordae tendinae instead consists of petal-like flaps of
tissue. The free borders of the cusps projects inwardly in the lumen of the corresponding
artery. In spite of the large forces generated the sagging in the centre of cusps is
prevented by maximal conglutination due orientation of collagen fibers, which in turn
helps to prevent regurgitation.
The aortic valve is tricuspid and is found between the left ventricle and the aorta. In the
aortic valve the three cusps are attached to the aortic wall by its convex outer margin.
Aortic cusps are thicker than the pulmonary cusps; both are thicker than the AV cusps.
Due to rise in pressure buid up in the left ventricle than in the corresponding the aortic
valve opens, allowing blood to enter aorta. As the ventricle relaxes blood starts flowing
back to heart, which causes the valve to close tightly.
Due some congenital heart abnormality bicuspid aortic valve is encountered in which
instead of normal three cusps the child has two and the condition is usually diagnosed
later in life until the person develops symptomatic aortic stenosis.
The atrioventricular valves so called because they separate the atria from the ventricles
and allow blood to flow from the atria to the ventricles preventing the opposite flow. The
tricuspid and bicuspid valve are known as AV valves. The right AV valve is called the
tricuspid valve and the left AV valve is called the mitral valve. Both the mitral and
tricuspid valves resemble the shape of parachute
During opening of AV valve, the pointed ends of the cusps project into the ventricle
forming a ring resembling the wide end of a funnel. The opening and closing of the AV
valves is pressure dependent due differences in pressure between the atria and ventricles.
To prevent the AV valve eversion i.e. turning inside-out these are attached to papillary
muscles by specialized strings of strong fibrous tissue called chordae tendineae which are
adhered to the muscle bundles in the chamber walls. Contraction of these muscles pulls
the chords, and the leaflets snap shut, closing off the heart chamber.
The tricuspid valve which is also known as right atrioventricular valve, is situated
between the right atrium and the right ventricle. The tricuspid valve is composed of three
fibrous segments primarily attached to the margin of the right atrioventricular opening
and in part to one another adjacent to the margin of the opening. Except for the
attachment to the papillary muscles the remaining of the edges are free. The chordae
tendineae are attached to the free margins as well at the central thickening of the cusp
because of which the ventricular portions of the valves become rough and the atrial ones
become smooth .
The mitral valve (also known as bicuspid valve) so called as it has two cusps separates
the left atrium from the left ventricle and opens to allow the oxygenated blood collected
in the left atrium to flow into the left ventricle. It opens in response to the increased
pressure from the left atrium due subsequent filling of blood. Due to rise pressure above
that of the left ventricle, the valve opens allowing blood to flow into the left ventricle
during rapid filling phase subsequent to atrial contraction and approaching closure during
the end of atrial contraction thus preventing back flow of blood.
Chordae tendineae are chords of fibrous connective tissue that bind mitral cusps to either
papillary muscles or to free end of left ventricular walls. Chordae tendinae are divided
into primary, secondary and tertiary and each chord has a different thickness. Closure of
the mitral valve and the tricuspid valve corresponds to the first heart sound. The sound is
actually produced by sudden cessation of blood flow caused by the closure of the mitral
and tricuspid valves rather closure of valve.