Female: differentiation of the canal system in the genital organ
During the 7th week the canal system of the female sex organs differentiates. The mesonephric duct and its tubules atrophy and out of the paramesonephric duct (Müller) arises the future fallopian tube, the uterus and the upper part of the vagina.
Sometimes, a few embryonic remnants of the mesonephric duct remain in the form of the epoöphoron, the paroöphoron at the level of the mesovarium, and a row of small cysts of Gartner.
Out of the upper, non-fused portion of the paramesonephric duct (Müller) arises the fallopian tube and its ampulla. The lower section fuses after it crosses medially on both sides of the inferior ovarian gubernaculum and forms the utero-vaginal canal. The medial septum in between disappears at the end of the 3rd month.
- Epoöphoron
- Paroöphoron
- Ovarian ligament
- Atrophied mesonephric duct (Wolff)
- Cysts of Gartner
- Hymen
- Suspensory ligament of ovary
- Fallopian tube (ampulla)
- Vesicular appendage (Morgani)
- Uterus
- Round ligament of uterus
- Vagina
- Insertion of the round ligament of uterus at the genital swelling
Shown is the atrophied mesonephric duct (Wolff) that, however, leaves certain embryonic remnants behind.
Out of the paramesonephric duct (Müller) arise on both sides the fallopian tubes and through fusion of both sides the uterus and the upper part of the vagina (blue).
The lower part of the vagina (yellow) comes from the urogenital sinus (endoderm).
To be noted is also the development of the ligaments and the hymen, the middle part of which usually disintegrates at around the time of birth.
Interactive diagram for comparing the differentiation of the internal sex organs in both sexes.
To be observed is the development of the ligaments. The ovarian gubernaculum gets attached on the developing utero-vaginal canal there where it goes over into the fallopian tube. Above it forms the ovarian ligament and below the round ligament of uterus, which goes through the inguinal canal and inserts in the female genital swelling (labia majora).
If the separating wall beyond the fusion location of the two paramesonephric ducts is not resorbed, various utero-vaginal abnormalities result.
7th – 8th weeks
- 1a
- Paramesonephric duct (Müller)
- 2a
- Mesonephric duct (Wolff)
- 3a
- Lower gubernaculum
- 4a
- Utero-vaginal canal
- 5a
- Urogenital sinus
Up to the 7th week two canal systems on each side exist in both sexes.
In the 8th week the paramesonephric ducts (Müller) fuse in the lower portion after they have crossed medially on both sides of the mesonephric duct (Wolff).
after 8 weeks
- 1a
- Paramesonephric duct (Müller)
- 2a
- Mesonephric duct (Wolff)
- 3a
- Lower gubernaculum
- 4a
- Utero-vaginal canal
- 5a
- Urogenital sinus
ca. 3rd month
- 1b
- Fallopian tube
- 2b
- Atrophied mesonephric duct (Wolff)
- 3b
- Ovarian ligament
- 3c
- Round ligament of uterus
- 4b
- Uterus
- 5b
- Vagina
Formation of the utero-vaginal canal through fusion of the lower section of the two paramesonephric ducts (Müller). From the upper section - on both sides - arise the fallopian tubes with their ampullae.
Fig. 45At the end of the 3rd month the separating wall dissolves in the uterus and the vagina. The uterus lengthens in that the solid lower end of the paramesonephric duct stretches in a downward direction and is subsequently canalized.
Out of the lower section arises the upper part of the vagina. It joins with the vaginal lamina, which arises from the urogenital sinus and forms the lower portion of the vagina.
The blind end of the utero-vaginal canal forms the sinu-vaginal eminence (stage 22) and ends at the back wall of the urogenital sinus (SUG).
The sinu-vaginal eminence becomes thicker due to epithelial proliferation and retracts, while the wall of the SUG also thickens there. These epithelial layers, which form at the lower end of the utero-vaginal canal, are known as the vaginal plate. At their cranial end they form a circular protrusion, the location of the future vaginal fornix.
ca. 7th week
- 1
- Genital tubercle
- 2
- Vestibule
- 2a
- Urovaginal sinus: pelvic part
- 2b
- Urovaginal sinus: phallic part
- 3
- Vaginal plate
ca. 12th week
- 4
- Perineum
- 5
- Rectum
- 6
- Utero-vaginal canal
- 7
- Urinary bladder
- 8
- Urethra
The utero-vaginal canal comes up against the urogenital sinus and forms the sinu-
vaginal eminence.
This sinu-vaginal eminence becomes thicker due to epithelial proliferation. This also leads to a epithelial proliferation in the SUG epithelium. Together they form the vaginal plate.
Through canalization of the vaginal plate the utero-vaginal canal opens itself towards the outside. The upper 3/4 of the vagina comes from the mesoderm and the lower fourth from the endoderm.
The fibromuscular walling forms from the neighboring mesenchyma. The vagina is separated from the SUG by the hymen. Its origin is not entirely clear. Discussed is a passive invagination of the back wall of the SUG.
ca. 3rd month
The canalization of the vaginal plate begins in the 3rd month.
ca. 5th month
ca. 9th month
- 2
- Vaginal vestibule
- 3a
- Uterine cavity
- 3b
- Uterine cervix (neck)
- 6a
- Vagina: The lower fourth out of endoderm
- 6b
- Vagina: The upper 3/4 out of mesoderm
- 9
- Hymen
In the 5th month the vaginal canal is completely canalized, but the lumen is separated from the SUG by the hymen.
Fig. 50Normally, the hymen tears open at the time of birth. The uterus and the vagina then have a connection to the vaginal vestibule.