What are the atrioventricular valves?
The heart contains four blood-regulating valves that act as doorways between its upper and lower chambers.
Two of these valves control blood flow into the heart and are known as atrioventricular valves. The mitral valve is the left atrioventricular valve. The tricuspid valve is the right atrioventricular valve.
Because the valves separate the atria (the two upper heart chambers – the right atrium and left atrium) and the ventricles (the two lower chambers – the left ventricle and right ventricle), the term “atrioventricular” is sometimes used to describe them.
What do the atrioventricular valves look like?
The atrioventricular valves are pliable structures made up of endocardium and connective tissue. Each valve is supported by a shape-retaining ring of tissue called an annulus and features leaflets or cusps that meet tightly during valve closure. The mitral valve has two leaflets. The tricuspid valve has three.
Attached to the leaflets of both valves are fibrous strings known as chordae tendinae. These heart strings connect to papillary muscles, which anchor to the walls of the ventricles. The papillary muscles (there are five) and chordae (jointly called the subvalvular apparatus) prevent the leaflets from prolapsing into the atrial chambers when they shut (as in mitral valve prolapse), preventing the backflow of blood.
What are the functions of the AV valves? How do they function?
The atrioventricular valves have two functions.
During the cardiac cycle, the atrioventricular valves enable the timely passing of blood from the atria to the ventricles when the valves open and prevent that blood from flowing back (regurgitating) into the atria when they shut. The mitral valve regulates blood that enters the left ventricle from the left atrium. The tricuspid valve controls blood entering the right ventricle from the right atrium.
Both valves open and close based on differences in chamber pressure. During ventricular relaxation, there is more atrial pressure, pushing open the AV valves and allowing blood into the ventricles. During ventricular contraction, there is more ventricle pressure, and the valves shut to form a seal.