Blood flows through the heart in one direction: from atria to ventricles and out the great arteries leaving the superior aspect of the heart. This one-way traffic is enforced by four valves that open and close in response to differences in the blood pressure on their two sides.
Atrioventricular (AV) Valves
These valves prevent the backflow of blood into the atria during ventricular contraction/ systolic phase of cardiac cycle.
The right atrioventricular (AV) valve has three cusps/flaps, therefore known as ‘tricuspid valve’, while, the left AV valve has two cusps and known as Bicuspid valve or the Mitral valve.
The cusps/flaps of the valves are anchored to the papillary muscles with the help of fine string-like structures, the chordae tendineae. This arrangement prevents the valves from being everted or blown inside out into the atrium during contraction of ventricles.
This parasternal ultrasound shows a healthy mitral valve (bottom) and aortic valve (top) at work. Can you figure out which is the atrium and which is the ventricle?
Aortic & Pulmonary (Semilunar) Valves
The bases of the two great distributing vessels (Pulmonary trunk and Aorta) issuing from the two ventricles also have valves.Blood from ventricles has to pass through these valves before entring the aorta and pulmonary trunk.
Both of these pulmonary and aortic valves have three pocket-like cusps, each shaped roughly like a crescent moon, hence, the name semi lunar.
These semi lunar valves prevent backflow of blood from the great vessels into the ventricles during ventricular relaxation or the diastolic filling phase of the cardiac cycle.
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