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 accessory sex glands

The accessory sexual glands originate from two epithelial tissues. They either come from the epithelial mesodermal origin of the mesonephric duct (Wolff) or from the epithelial endodermal origin of the urogenital sinus.

The seminal vesicle differentiates itself during the 12th week from a protrusion on the deferent duct, near where it opens at the back wall of the urogenital sinus (future prostatic part of the urethra). They thus have a mesodermal origin. These paired glands produce a viscous, fructose-rich secretion that serves as a source of energy for the sperm cells. The portion of the mesonephric duct that lies between the junction of the seminal vesicle and the prostatic part of the urethra is called the ejaculatory duct. Between the two ejaculatory duct junctions the prostatic utricle (remainder of the paramesonephric duct) has its opening. This location is called the seminal colliculus.

Fig. 37
Median sagittal section at the level of the prostate shows the development and differentiation of the seminal vesicle and the prostate

The prostate develops from a protrusion on the dorsal wall of the prostatic part of the urethra during the 12th week. The prostate's glandular epithelium develops, therefore, from cells that have their origin in the endoderm, while the stroma and smooth muscle develops from cells with a mesodermal origin - under the inducing influence of DHT (see: hormonal factors in sex differentiation). The glands become active after the 15th week and surround the two ejaculatory ducts and the prostatic utricle as well as the prostatic part of the urethra.

Over the course of the 12th week and parallel to the development of the prostate, bulbourethral (Cowper's) and urethral (Littre's) glands form, originating in pairs of endodermal protrusions of the spongy part of the urethra, which follow from the prostatic membranous parts. Finally, the seminal fluid is augmented by secretions from the seminal vesicle, the prostate, the bulbourethral and urethral glands.

Fig. 38
Schematic front section through the male sex canals shows the differentiated accessory glands.