University:
Stanford University
Course:
MED 101 | Human Anatomy
Academic year:

2023
Views:

285

Pages:

2
Author:

larbi43100

THE FACTORS OF SEXUAL DIFFERENTIATION During the development of the urogenital system, the morphological transformations described above take place in several stages controlled by factors which intervene successively. Normal development requires the harmonious intervention of this “cascade of factors” on all the constituents of the urogenital system. 1. Chromosomal determinism The first determining step occurs at the time of fertilization according to the sex chromosome of the fertilizing sperm. If it is a Y chromosome, the zygote will have the chromosomal formula 46 XY and differentiation will take place towards masculinization. If it is an X chromosome, the zygote will have the chromosomal formula 46 XX; in the absence of a Y chromosome, differentiation will move towards feminization. 2. Testicular differentiation factor This factor, called TDF (testis determining factor), is a protein encoded by an SRY gene located on the short arm of the Y chromosome which is expressed in the cells of the wall of the sexual cords and induces their organization into testicular cords. Other genes could be involved, in particular the SOX 9 gene. 3. Hormonal factors Hormonal factors will directly or indirectly induce other transformations of the genital system. In the male sex At the level of the fetal testicle, the Sertoli cells secrete a antiMüllerian hormone (AMH) which will cause the regression of the Müllerian ducts from the 8th week, they also have an inducing role for the development of Leydig cells of the interstitial tissue. Leydig cells, upon their individualization, secrete testosterone. During differentiation this hormone induces the development of Wolffian ducts and their derivatives, later during fetal life they induce the masculinization of organs which present sexual dimorphism and, at puberty, the organization of the tubes seminiferous and the triggering of spermatogenesis. At the level of the derivatives of the wall of the urogenital sinus and the external genital organs, masculinization (formation of the prostate and bulbourethral glands) also depends on the presence of male hormone but the tissue receptors are only stimulated by the presence a reduced form of testosterone, dihydrotestosterone (DHT). This reduction requires the presence of an enzyme, 5α reductase. In the female sex In the absence of TDF, the undifferentiated gonad transforms into a fetal ovary: the sex cords fragment and during fetal life, the cells are organized into follicles around the germ cells which become oogonia (meioses are triggered at from the 5th month). In the absence of anti-Müllerian hormone, paramesonephrotic ducts develop into the tubes and the uterovaginal canal. In the absence of testosterone, the Wolffian ducts regress, the posterior wall of the urogenital sinus gives rise to the vaginal plate and the external genitalia change little.