21.4 Development of the internal genital organs

• Indifferent stage
• In males:
  • Differentiation of the canal system in the genital organ
  • Differentiation of the accessory sex glands
  • Differentiation of the urogenital sinus
• In females:
  • Differentiation of the canal system in the genital organ
  • Differentiation of the accessory sex glands
  • Differentiation of the urogenital sinus
• Summary: Development of the internal genital organs

In males: Differentiation of the canal system in the genital organ

The differentiation of the male sex organ canals is influenced by the testosterone hormone that is produced from the 8th week in the fetal testis by Leydig's interstitial cells.

Fig. 36
The paramesonephric duct (Müller) atrophies (shown in blue).
The mesonephric duct (Wolff) differentiates itself further (shown in pink).
The two ejaculatory ducts as well as the prostatic utricle (which will have a dead end due to the atrophy of the paramesonephric duct) empty into the seminal colliculus.

Two phenomena mark the differentiation of the canals of the internal male sex organs:

1. The atrophy of the paramesonephric duct (Müller)
2. The development and differentiation of the mesonephric duct (Wolff)

The mesonephric duct (Wolff) atrophies cranially and leaves behind only the epididymal appendage as an embryonic rudiment. On both sides the parts of the mesonephric duct, which lie across from the testes, form the epididymis. The testis and the epididymis of both sides are partially enveloped by the tunica vaginalis testis (serous bilaminar membrane with a periorchium [ = outermost layer] and epiorchium [ = inner layer]). In the part of the epididymis are end the efferent ductules. They originate from the mesonephric tubules, and so form the beginning of the epididym. Immediately afterwards it coils tightly and finally goes into the lower part of the epididymis (its tail) and over into the deferent duct. This is a musculo-epithelial tube that, during ejaculation, dispatches the sperm cells from the epididymis into the urethra.

In the male fetus - between the 8th and 11th week - the paramesonephric duct atrophies due to the effects of the antimüllerian hormone (AMH), which is formed by precursors of Sertol's supporting cells (cells that surround the primordial germ cells and come from the primitive gonadal cords). Despite the effects of this hormone, embryonic remnants of the paramesonephric duct remain behind in males. These are the testicular appendage at the cranial pole of the testis and the prostatic utricle at its caudal pole.