Heart Valves

The heart contains four main valves that maintain unidirectional blood flow through its chambers and into the great vessels. These valves function passively, opening and closing in response to pressure changes during the cardiac cycle. They are divided into atrioventricular valves (between atria and ventricles) and semilunar valves (between ventricles and great arteries).

Types of Heart Valves

• Atrioventricular (AV) valves: Tricuspid valve and Mitral (bicuspid) valve
• Semilunar valves: Pulmonary valve and Aortic valve

Atrioventricular Valves

Tricuspid Valve

• Location: Between the right atrium and right ventricle
• Cusps: Three (anterior, posterior, septal)
• Function: Prevents backflow of blood from the right ventricle into the right atrium during systole

The tricuspid valve is supported by chordae tendineae, which attach the valve cusps to papillary muscles in the right ventricle. When the ventricle contracts, the papillary muscles also contract to prevent valve prolapse.

Mitral Valve (Bicuspid Valve)

• Location: Between the left atrium and left ventricle
• Cusps: Two (anterior and posterior)
• Function: Prevents backflow of blood from the left ventricle into the left atrium during systole

The mitral valve is the only valve with two cusps. Like the tricuspid valve, its cusps are tethered by chordae tendineae to anterior and posterior papillary muscles. It is structurally more robust due to higher left ventricular pressure.

Semilunar Valves

Pulmonary Valve

• Location: Between the right ventricle and the pulmonary trunk
• Cusps: Three (anterior, left, right)
• Function: Prevents backflow of blood into the right ventricle during diastole

The cusps of the pulmonary valve form pocket-like structures. When the right ventricle relaxes, blood tends to flow back toward the heart, but this fills the cusps and forces them shut, preventing regurgitation.

Aortic Valve

• Location: Between the left ventricle and the ascending aorta
• Cusps: Three (left, right, and posterior)
• Function: Prevents backflow of blood into the left ventricle during diastole

Each cusp of the aortic valve is associated with an aortic sinus (sinus of Valsalva). The right and left coronary arteries originate from the corresponding aortic sinuses. Closure of the aortic valve helps direct blood into these arteries during diastole.

Valve Histology

All heart valves are composed of three layers:

• Fibrosa: Dense collagen core providing tensile strength
• Spongiosa: Loose connective tissue acting as a shock absorber
• Ventricularis or Atrialis: Elastic fibers facing the ventricular or atrial side, respectively

Valves are covered by endothelium continuous with that of the endocardium. They are avascular and rely on diffusion from the blood for nourishment.

Associated Structures

Chordae Tendineae

Fibrous cords that connect the free edges of AV valve cusps to papillary muscles. They prevent eversion of the valves during ventricular contraction.

Papillary Muscles

Muscular projections from the ventricular walls. They contract during systole to maintain tension in the chordae tendineae.

Topographic Summary

• Tricuspid Valve: Right atrioventricular opening; three cusps
• Mitral Valve: Left atrioventricular opening; two cusps
• Pulmonary Valve: Right ventricular outflow; three semilunar cusps
• Aortic Valve: Left ventricular outflow; three semilunar cusps with coronary origins