Atrioventricular valves

The atrioventricular valves are two of the four valves within the heart, the other two valves being the semilunar valves.

The atrioventricular valves are located between the the atria and the ventricles of the heart. The atrioventricular valve between the left atrium and the left ventricle is called the bicuspid valve (also known as the mitral valve), and the atrioventricular valve between the right atrium and the right ventricle is called the tricuspid valve.

In each case, as the atrium of the heart contracts it pushes a quantity of blood into the corresponding ventricle. The atrioventricular valve consists of dense connective tissue covered by endothelium. It acts to prevent blood from flowing backward from the ventricle to the atrium. That is important because the next action in the sequence is the contraction of the ventricle to push the blood out of the heart into an artery for transport to the next organ around the body.

The opening and closing of the atrioventricular valves is controlled by the differences in pressure across them:

• When blood passes from an atrium to a ventricle, the atrioventricular valve is pushed open (and the papillary muscles relax and the chordae tendineae lose their tension, becoming slack).
• At the next stage in the sequence the ventricle contracts. This forces blood out from the ventricle into the artery via which it leaves the heart. This contraction of the ventricle and the corresponding increase in blood pressure within that ventricle also presses the cusps of the atrioventricular valve together until their edges meet, closing the valve. At the same time, the papillary muscles contract and the chordae tendineae tighten - both of which also help to prevent the cusps from enabling the atrioventricular valves to open.

When in the next stage of the sequence, the ventricle relaxes and the atrium contracts, the blood pressure situation is reversed: The relaxation / tension of the papillary muscles and the chordae tendineae also reverses and the atrioventricular valve allows blood to pass from the atrium to the ventricle again.