Valves of the Heart
There are four valves which are flap-like structures that function to maintain unidirectional (forward) blood flow through the heart chambers. These valves open and close in response to pressure and volume changes within the cardiac chambers. There are two atrio-ventricular valves which separate the atria from the ventricles and two semi-lunar valves which separate the pulmonary artery and the aorta form their respective ventricles.
Atrio-ventricular valves are the tricuspid and bicuspid (mitral) valves. The tricuspid valve located between the right atrium and right ventricle contain three leaflets held in place by fibrous cords called chordae tendinae. The chordae tendinae in turn are anchored to the ventricular wall by the papillary muscles.
The bicuspid or the mitral valve located between the left atrium and left ventricle has two valve cusps or leaflets. It is attached in the same manner as the tricuspid valve. The chordae tendinae support the valves during ventricular systole to prevent valvular porlapse into the atrium. Damage to the chordae tendinae or to the papillary muscles would permit blood to regurgitate into the atrium during ventricular systole. AV valves are closed during ventricular systole and open during ventricular diastole.
The semi-lunar valves consist of three cup-like cusps. They lie between each ventricle and the great vessels into which it empties. These valves can open during ventricular systole to permit blood flow into aorta and pulmonary artery and closed during diastole to prevent retrogarde flow form the aorta of pulmonary artery back into the ventricles when it is relaxed.