**7. Functional anatomy**

The aortic root is a complex structure that requires analysis part by part but always remem‐ bering that all the parts contribute to form one functional unit, a three-dimensional structure adjoining distally to the aorta and proximally to the ventricle.

The aortic valve, like the pulmonary valve, has no tensor apparatus (i.e., chordae tendineae or papillary muscles). The commissures form tall, peaked spaces between the attachments of adjacent leaflets and attain the level of the aortic sinotubular junction, the ridge that sepa‐ rates the sinus and tubular portions of the ascending aorta. The functional aortic valve ori‐ fice can be at the sinotubular junction or proximal to it. [42]

The three half moon-shaped leaflets form pocket-like tissue flaps that are avascular. Just be‐ low the free edge of each leaflet is a ridgelike closing edge. At the center of each leaflet, the closing edge meets the free edge and forms the nodule of Arantius. Between the free and closing edges, to each side of the nodule are two crescent-shaped areas known as the lunu‐ lae, which represent the sites of leaflet apposition during valve closure. Lunular fenestra‐ tions, near the commissures are common and increase in size and incidence with age. [43] However, owing to their position distal to the closing edge, they rarely produce valvular in‐ competence. [42] When viewed from above, the linear distance along the closing edge of a leaflet is much greater than the straight-line distance between its two commissures. This ex‐ tra length of leaflet tissue is necessary for nonstenotic opening and nonregurgitant closure of the valve. [6] Normally, the diameter of the aortic annulus at the hinge points of the aortic valve is about equal to the diameter of the ascending aorta at the sinotubular junction. [44] When the valve opens, the leaflets fall back into their sinuses without the potential of oc‐ cluding any coronary orifice. The semilunar hingelines of adjacent leaflets meet at the level of the sinotubular junction, forming the commissures. The body of the leaflets are pliable and thin in the young, although its thickness is not uniform.

The commissure between the right and posterior aortic leaflets overlies the membranous septum and contacts the commissure between the anterior and septal leaflets of the tricuspid valve. The commissure between the right and left aortic leaflets contacts its corresponding pulmonary commissure and overlies the infundibular septum. The intervalvular fibrosa, at the commissure between the left and posterior aortic cusps, fuses the aortic valve to the an‐ terior mitral leaflet. [6, 42]

A study of 100 formalin-fixed hearts from adult patients with normally functioning aortic valves found that the luminal area of the aorta at the sinotubular junction increased with age and with heart weight, where increased heart weight was attributed to systemic hyperten‐ sion. [45] Volume-wise, the sinuses are largest when the valve closes, serving as reservoirs during ventricular diastole and allow filling of the coronary arteries.

When left ventricular pressure exceeds that in the aortic root, the valvular leaflets are pushed apart and fall back into their respective sinuses, allowing unimpeded ejection of blood. The orifices of the coronary arteries are commonly found close to the level of the sinotubular junction. [25]
