[Ultrastructural study of the human bladder trigone].

To assess the ultrastructural appearance of the trigonal epithelium in the young human female, 12 biopsies in the trigonal area have been studied by transmission electron microscopy. The trigonal epithelium is of the stratified squamous nonkeratinizing type and is composed of about twenty cellular layers undergoing a progressive involution from the basal layer toward the surface. In the basal and intermediate layers, Langerhans cells were found, which contain Birbeck granules. As in the urothelium, the intercellular spaces are very distended between the junctional desmosomes. That the trigone has the same embryological origin as the vagina is discussed. It explains the reactivity of the trigonal epithelium to estrogens. Urocytogram is a practical application of these facts.