Testicular differentiation: The male gonad develops into the testis toward week 7 of development. Until
then, it is undifferentiated. The differentiation is determined by the XY genetic constitution and proceeds
as follows
THE PRIMARY SEX CORDS, proliferating from the coelomic epithelium, condense and extend into the medulla
of the gonad.
In the medulla, the cords branch, their deep ends anastomose, and they form the rete testis
The prominent sex cords become the seminiferous or testicular cords which soon lose their connections
with the germinal epithelium because of the development of a thick fibrous capsule, the tunica albuginea
The tunica albuginea is a layer of connective tissue which is interposed early, between the coelomic
epithelium (parietal peritoneum) and the rest of the glan It produces partitions which compartmentalize
the gland, closing off the seminiferous ducts, about day 50, into testes cords
Development of the tunica albuginea is a characteristic and diagnostic feature of testicular development
The seminiferous or testicular cords develop into the seminiferous tubules, whose deep portions
narrow to form the tubuli recti, which converge on the rete testis
The seminiferous tubules become separated by mesenchyme which gives rise to the interstitial cells
of Leydig
It is here that the androgenic hormones are secreted which help in the differentiation of the genital
tract and the external genital organs
The interstitial cells of Leydig reach their maximum development between 3 1/2 and 4 months
The walls of the seminiferous tubules, as a result of their cellular duality of origin, are composed
of 2 types of cells: supporting or sustentacular cells of Sertoli, derived from the germinal
epithelium, and the spermatogonia, derived from the primordial germ cells (unlimited in number,
in contrast to the oogonia)
The cells of Sertoli make up most of the seminiferous epithelium in the fetal testis
Gradually, the enlarging testis separates from the regressing mesonephros and is suspended by its own
mesentery, the mesorchium
IN LATER DEVELOPMENT, THE GERMINAL EPITHELIUM flattens to form the mesothelium on the surface of the
testis and the rete testis becomes continuous with the 15 to 20 adjacent persistent mesonephric tubules
The persistent mesonephric tubules, after regression of the mesonephric (wolffian) body, participate
in the formation of the excretory tracts of the testis, forming the vasa efferentia or efferent ductules
The efferent ductules open into the adjacent mesonephric duct which becomes the ductus epididymidis
(epididymis)
Thus, the vasa efferentia and the epididymis are of mesonephric origin