21.4 Development of the internal genital organs



In females: Differentiation of the accessory sex glands


The accessory glands arise from the endoderm of the SUG:

  • The greater vestibular glands (Bartholini) are paired glands that form in the course of the 12th week from the endoderm of the SUG. The outflow canals empty sideways in the vaginal vestibule. They correspond to the bulbourethral gland (Cowper) in males.

  • The lesser vestibular glands (Skene) or paraurethral glands also form from epithelial buds (endoderm) of the SUG and grow into the neighboring mesenchyma. They are distributed over the whole vaginal vestibule and - in males - correspond to the prostate.



In females: Differentiation of the urogenital sinus

Quiz

Quiz 14

In females the cranial portion of the pelvic part of the definitive SUG remain narrow and forms the female urethra, which is very short.
With the progressing development the caudal portion of the pelvic part shrinks and becomes included in the phallic part (vaginal vestibule). Therein discharge the urethra and the vagina.
The phallic part of the definitive SUG enlarges to become the vaginal vestibule that is caudally closed off externally by the urogenital membrane. It then tears in the course of the 7th week 19.

Fig. 51 - Urogenital sinus (SUG)
ca. 12th week		 Fig. 52 - Vaginal vestibule of the uterus
and vagina, ca. 9th month		  Legend

1
2
2a
2b
3
4
5
6
7
8		 Genital tubercle
Vestibule
SUG: Phallic part
SUG: Lower part of the pelvic part
Vaginal plate
Perineum
Rectum
Utero-vaginal canal
Urinary bladder
Urethra: From the upper portion of the pelvic part of the definitive SUG

2
3a
3b
6a

6b

9		 Vaginal vestibule
Uterine cavity
Uterine cervix
Vagina: Lower fourth out of endoderm
Vagina: Upper 3/4 out of mesoderm
Hymen

Fig. 51
In females, the development of the SUG begins in the 3rd month, at the same time as the formation of the vagina.

Fig. 52
The pelvic part of the SUG has shrunk and will be retracted into the phallic part in order to form the definitive vaginal vestibule.


Summary:
From the paramesonephric duct (Müller) arises:
  • Uterus
  • Fallopian tube
  • Vagina (3/4)

From the SUG endoderm arises:

  • Vagina (1/4)
  • Urethra
  • Vaginal vestibule
  • Urethral glands, para-urethral and vestibular

Overview

Formation of the ovaries and the female genitalia

Overview

The embryonic structures and their derivatives in both sexes


Summary: Development of the internal genital organs



In males the internal sex organs come from the mesonephric duct (Wolff) that differentiates itself into the epididymis, deferent duct, seminal vesicle and the ejaculatory duct. The paramesonephric duct (Müller) atrophies. It leaves behind embryonic remnants such as the testicular appendage (hydatid) and parts of the prostatic utricule.

In females the paramesonephric duct (Müller) remains in existence and differentiates itself into the fallopian tube with its ampullae and, following its fusion at the caudal end, into the uterus and the upper part of the vagina. The mesonephric duct (Wolff) with its tubules atrophies and leaves embryonic remnants such as the ductus longitudinalis epoöphori (Gartner), epoöphoron and paroöphoron.

More info

The embryonic remnants of the mesonephros and Paramesonephros.


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