Cardiac Histology (VIII): Atrioventricular valves (Mitral and Tricuspid part 1)

D . Light micrograph of the mitral valve of a fetus, showing a somewhat myxoid stroma without differentiation into the layered structure of the adult valve. The atrial side of the valve is indicated (auricularis) ( H&E , 50 X). E. Histologic section of the valve shows plump cells embedded in the myxoid matrix. Note the single layer of endothelial cells lining the surface of the valve. F. Scanning electron micrograph showing a mosaic-like pattern of arrangement of the endothelial cells. A prominent bulge corresponds to the nucleus in the central portion of the cell. Small, scant microvilli are present. ( 2,500 X) G. Low magnification micrograph of a section of the mitral valve. The layers of the atrioventricular valves vary slightly according to the region (whether basal or distal) of the leaflet. The fibrosa is the most consistent layer. It is formed by collagenous (yellow) bundles. The spongiosa contains loosely arranged connective tissue, proteoglycans and small amounts of elastic fibers. It is most prominent in the basal portion of the valve. The auricularis is also rich in proteoglycans and is located on the atrial side of the proximal portions of the valve (not shown) (Movat pentachrome, 25X). H. Basal portion of the valve. View of the ventricularis, which is subjacent to the endothelium of the ventricular aspect of the valve and is rich in proteoglycans and elastic fibers. (Movat pentachrome, 20X)

The atrioventricular valves show further specialization to withstand the constant trauma and pressure load of the cardiac cycle. Their design is unparalleled by any prosthetic device. The following image will show you how the adult atrioventricular valves have specialized histological components that match their function.