Intermediate - Heart Valves
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There are four valves in the adult heart, depicted below. There are two AV valves which comprise leaflets as well as the structures that tether these leaflets to the ventricular walls. The aortic and pulmonary valves, termed the semilunar valves, are located in the aorta and pulmonary trunk respectively. They are each made of three cusps.
The AV valves begin to form between the fifth and eighth weeks of development. The left AV valve has anterior and posterior leaflets and is termed the bicuspid or mitral valve. The right AV valve has a third, small, septal cusp and thus is called the tricuspid valve. The valve leaflets are attached to the ventricular walls by thin fibrous chords: the chordae tendineae, which insert into small muscles attached to the ventricle wall: the papillary muscles. These structures are sculpted from the ventricular wall (see left).
The semilunar valves are formed from the bulbar ridges and subendocardial valve tissue. The primordial semilunar valve consists of a mesenchymal core covered by endocardium. Excavation occurs, thinning the valve tissue thus creating its final shape (see right).
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Aortic valve: Three-leaflet valve located at the junction between the left ventricle and aortic entrance.
Bulbar ridges: Endocardial cushion tissue located in the bulbus cordis extending into the truncus arteriosus thus forming ridges. These fuse together to form the aorticopulmonary septum.
Chordae tendineae: Cord-like tendons connecting the papillary muscles to the leaflets of the mitral and tricuspid valves.
Mitral valve: (Bicuspid valve) two leaflet valve located on the left side of the heart i.e. between the left atrium and ventricle.
Papillary muscles: Small muscles found on the inner myocardium of the left and right ventricles. They are attached to the mitral and tricuspid valves via the chordae tendineae and serve to limit the movements of the valves.
Pulmonary valve: Three-leaflet valve located at the junction between the right ventricle and the pulmonary trunk.
Semilunar valves: Flaps of endocardium and connective tissue reinforced by fibres which prevent the valves from turning inside out. They are shaped like a half moon, hence the name semilunar. The semilunar valves are located between the aorta and the left ventricle and between the pulmonary artery and the right ventricle.
Trabeculae (trabeculations): Muscular beams located within the ventricles and parts of the atria of the heart.
Tricuspid valve: Three leaflet valve located in the right atrioventricular canal i.e. between the right atrium and ventricle.