Heart Valves

• Ensure unidirectional blood flow through the heart and great vessels.
• Comprise fibroelastic tissues; specifically, a collagenous core covered by endocardium.

Comprise three cusps, aka, leaflets, that prevent backflow to the ventricles.

• Trap blood within the sinuses of the aorta and pulmonary trunk.

During diastole, the semilunar valve leaflets fall open to trap blood in the sinuses, thus preventing backflow into the ventricles. The coronary arteries run into the right and left aortic sinuses. Annulus* is the ring-like network of fibrous tissue that attaches the leaflets to the vessel wall. It's not really a perfect circle of continuous fibrous tissue, but instead comprises elements that are dynamically responsive to heart contractions. Nodule* (aka, nodule of Arantius), is a thickened spot in the middle of the free edge of the leaflet. Lunule* is the free edge of the leaflet. Commissures* are where the leaflets attach to the wall. Sinotubular junction* passes through the commissures and signifies the transition from the sinus to the vessel. Pulmonary valve comprises an anterior, right, and left leaflet; they ensure unidirectional flow of deoxygenated blood from the right ventricle to the lungs. Aortic valve comprises right coronary, left coronary, and posterior non-coronary leaflets; leaflet names reflect their relationships to the ostia of the coronary arteries. The aortic semilunar valve ensures unidirectional flow of oxygenated blood from the left ventricle to systemic circulation. Are attached to the papillary muscles via chordae tendineae (tendinous cords), which comprise a network of collagenous and elastic fibers. Papillary muscles* are special extensions of the myocardium that anchor the valve leaflets. Annular ring* is a fibrous structure that anchors the leaflets to the heart. Bicuspid valve, aka, mitral valve, is on the left. – It comprises two primary cusps (hence, "bi" & "cuspid"), anterior and posterior, which ensure unidirectional flow of oxygenated blood from the left atrium to left ventricle. Each primary cusp can be further subdivided into three regions (Anterior 1-3 and Posterior 1-3). Tricuspid valve is on the right. – It comprises anterior, posterior, and septal leaflets, which ensure unidirectional flow of deoxygenated blood from the right atrium to right ventricle.