BGDB Sexual Differentiation - Fetal
Practical 12: Sex Determination | Early Embryo | Late Embryo | Fetal | Postnatal | Abnormalities | 2011 Audio |
Introduction
In the previous section we observed late embryonic male genital development and now in fetal development we will observe early fetal female development. Then we will explore fetal development of the external genitalia and gonadal descent.
Week 10 Female
- week 10 to 12 - female in absence of Sry expression, within the gonad cortical cords extend from the gonad surface epithelium. Primordial germ cells which have entered the gonad form oogonia primordia, surrounding mesenchyme forms the follicular primordia.
- The selected images below show the general anatomy of the pelvic region of the an early female fetus (10 week, 40mm).
- This first image shows the relative positions of the kidney (plane A most lateral) and developing ovary (plane A and B away from the midline) and internal genitalia (plane C and D in the midline).
- The selected images below show sections through the pelvic region showing anatomical relationships between the developing female gonad (ovary), internal genital tract and external genitalia.
- Note the relative immaturity of the external genitalia, which at this time would appear identical to the male.
Uterus and Vagina
Mouse paramesonephric duct (Müllerian duct)[1] |
This mouse image shows the relationship between the mesonephric and paramesonephric ducts opening into the urogenital sinus.
|
This graph shows the growth during the fetal period of the uterus between week 19 and 38. During this time the uterine circumference increases from 20 mm to just under 60mm and the width increases from less than 10mm to just over 20 mm.
Uterine horn fimbrial development begins after week 20 and continues after birth.
Uterine growth continues postnatally, increasing outer muscle thickness and cyclic changes in the lining with puberty.
(Data: Soriano D, Lipitz S, Seidman DS, Maymon R, Mashiach S, Achiron R. Development of the fetal uterus between 19 and 38 weeks of gestation: in-utero ultrasonographic measurements. Hum Reprod. 1999 Jan;14(1):215-8.)
External Genitalia
This next section will look at the development of the external genitalia using a series of animations and online resources.
Female External Genitalia
Male External Genitalia
External Genitalia Comparison
Gonad Descent
This looped animation shows the descent of the gonads and their blood supply.
Internal Gonad Descent
Testes Descent
This looped animation shows the descent of the testes between Week 7 and 38 (birth).
The testis (white) lies in the subserous fascia (spotted) a cavity processus vaginalis evaginates into the scrotum, and the gubernaculum (green) attached to the testis shortens drawing it into the scotal sac. As it descends it passes through the inguinal canal which extends from the deep ring (transversalis fascia) to the superficial ring (external oblique muscle). Descent of the testes into the scrotal sac begins generally during week 26 and may take several days. The animation shows the path of a single testis. Incomplete or failed descent can occur unilaterally or bilaterally, is more common in premature births, and can be completed postnatally. (see also cryptorchidism).
Abdominal muscles : external oblique (purple), internal oblique (blue), transverse abdominus (pink)
Fascia: transversalis (red), subserous (spotted), peritoneum (orange)
Testes Descent | Testes Descent Large
Testes Descent Timeline
Data from a recent study of male human fetal (between 10 and 35 weeks) gonad position.
10 to 23 weeks - (9.45%) had migrated from the abdomen and were situated in the inguinal canal
24 to 26 weeks - (57.9%) had migrated from the abdomen
27 to 29 weeks - (16.7%) had not descended to the scrotum
A second study showed that from 33 weeks fetal testes had descended to the scrotum and that between 33 to 40 weeks (term) both testes have normally descended to the scrotum. Failure of descent (cryptorchidism) either unilateral or bilateral testicular descent, occurring in up to 30% premature and 3-4% term males.
References: Sampaio FJ, Favorito LA. Analysis of testicular migration during the fetal period in humans. J Urol. 1998 Feb;159(2):540-2. | Malas MA, Sulak O, Ozturk A. The growth of the testes during the fetal period. BJU Int. 1999 Oct;84(6):689-92.
Practical 12: Sex Determination | Early Embryo | Late Embryo | Fetal | Postnatal | Abnormalities | 2011 Audio |
References
- ↑ <pubmed>12297555</pubmed>
BGDB: Lecture - Gastrointestinal System | Practical - Gastrointestinal System | Lecture - Face and Ear | Practical - Face and Ear | Lecture - Endocrine | Lecture - Sexual Differentiation | Practical - Sexual Differentiation | Tutorial
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Cite this page: Hill, M.A. (2024, May 4) Embryology BGDB Sexual Differentiation - Fetal. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/BGDB_Sexual_Differentiation_-_Fetal
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G