Development of sexual dimorphism in human urogenital sinus complex.

The histological differentiation of the human fetal prostatic urethra and the corresponding part of human fetal female urethra was studied during the 10th through 14th weeks of ovulation age. The development of all the prostatic glands started as epithelial outgrowths from the urethral wall of the urogenital sinus during the time covered in this study. These outgrowths grew rapidly in number and size, especially the posterior ones, and no outgrowths were seen from the paramesonephric and mesonephric ducts. However, the more columnar epithelial cells on the colliculus seminalis, from which the middle and posterior lobes developed, may be of different embryonic origin, e.g. mesonephric, paramesonephric and urethral, or may react differently to hormonal factors. The possible differences in the origin and in the morphological differentiation of the epithelial cells may give clues to the differences in localization of neoplastic changes in adult prostate. The gland formation was preceded by mesenchymal changes which progressed during acinic morphogenesis. Mesenchymal cells differentiated into fibroblasts forming a lamina propria the primitive acini. The mesenchymal differentiation in the corresponding part of the female urethra was not equally prominent. However, the increase in urethral epithelial cells density and cell size was more prominent in the females. These morphological differences might be regulated by sex steroids and further strengthen the current view of the role of the mesenchyme in the prostatic morphogenesis.