The right atrioventricular valve is called 'tricuspid valve' because it consists of three cusps. These are triangular flaps which close and open simultaneously to regulate the flow of blood from the right atrium into the right ventricle during systole and diastole (cardiac muscle contraction and relaxation, respectively). Action: it prevents the backflow of blood from the cavity of the right ventricle into the cavity of the right atrium.
The right atrioventricular valve is composed of a medial cusp (cuspis septalis), an inferior cusp (cuspis posterior), and an anterior cusp (cuspis anterior). All three flaps project into the cavity of the right ventricle. The medial cusp is closest to the ventricular septum and is attached to the medial portion of the right atrioventricular orifice. The inferior cusp, on the other hand, is smaller and it is affixed to the postero-lateral periphery of the orifice. The anterior cusp is the smallest of the tree, and it is anchored to the anterior periphery of the atrioventricular orifice.
The three cusps of this valve shuts tight, checking the downward blood flow, during each myocardial contraction (systole), and open to let it flow again during muscle relaxation (diastole). The three flaps opens up during heart muscle relaxation (diastole) and they close tightly during cardiac muscle contraction (systole), due to the blood pressure. The chordae tendineae, which are string-like tendinous chords attached to the edges of the cusps, prevent them from caving upwards into the atrium during ventricular contraction. The papillary muscles are located on the wall of the ventricle.
The atrioventricular valve action of checking the blood flow tight is to avoid regurgitation, which is the backflow of deoxygenated blood from the right ventricle back into the right atrium. This can happen sometimes when the valve is damaged and there is valvulary insufficiency.
Below, longitudinal cut of the right side of heart (side view), showing the right atrium, right ventricle and the tricuspid valve.
