Female: 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.
Female: differentiation of the urogenital sinus
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 (stage 19).
ca. 12th week
- 1
- Genital tubercle
- 2
- Vestibule
- 2a
- SUG: Phallic part
- 2b
- SUG: Lower part of the pelvic part
- 3
- Vaginal plate
- 4
- Perineum
- 5
- Rectum
- 6
- Utero-vaginal canal
- 7
- Urinary bladder
- 8
- Urethra: From the upper portion of the pelvic part of the definitive SUG
- 2
- Vaginal vestibule
- 3a
- Uterine cavity
- 3b
- Uterine cervix
- 6a
- Vagina: Lower fourth out of endoderm
- 6b
- Vagina: Upper 3/4 out of mesoderm
- 9
- Hymen
In females, the development of the SUG begins in the 3rd month, at the same time as the formation of the vagina.
Fig. 52The 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
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.
Interactive diagram for comparing the differentiation of the internal sex organs in both sexes.