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
Internal Gonad Descent
Testes Descent
Start of testis descent | End of testis descent |
Additional Information
Testes Descent Timeline
Data from a study of male human fetal (between 10 and 35 weeks) gonad position.[2]
- 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 looked at the position of the testes[3]
- 33 weeks fetal testes had descended to the scrotum
- 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.
Practical 12: Sex Determination | Early Embryo | Late Embryo | Fetal | Postnatal | Abnormalities | 2011 Audio |
References
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, April 26) 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