Development of the Male and Female Sexual and Reproductive Organs Inside the Womb: What They Have in Common

What came first, the chicken or the egg? While we do not know the answer to this question, we do know all humans start out being physically female, even though genetically they may be male. For the first eight weeks of our existence, both male and female fetuses have the same rudimentary reproductive and sexual organs. In the early stages of fetal development the maternal hormones control the development of the reproductive organs, as the fetus is incapable of producing its own. It is not until the twelfth week of development that you can start to visually determine the sex of a fetus. The image below demonstrates how even after more than twelve weeks, they still look very similar.

Medical Quote:

Originally Published: July 2010

In mammals, phenotypic sex [visible sexual characteristics] is determined by a single gene—called Sry—on the Y Chromosome. This sex-determining region of the Y chromosome codifies for the protein tdf, for testis determining factor, a transcription factor which initiates a cascade of gene expression and protein products that will direct development of the bipotential gonadal anlage toward testis. In the absence of the Sry gene, this same gonadal anlage will become an ovary. The brain is also sexually differentiated in males and females by gonadal steroid hormones and this process occurs during a restrictive development window termed the sensitive period...In primates, including humans, the sensitive period is largely prenatal, beginning in the 2nd trimester, and the critical hormone for masculinization is testosterone (T).

Source

It is for this reason that male and female reproductive and sexual organs are more alike than they first appear. The clitoris is actually a penis that is not fully developed, or another way of looking at it, a penis is a fully developed clitoris. As with a penis, the clitoral glans and shaft become engorged with blood during sexual arousal. When the clitoris becomes well developed it looks similar to a small penis, minus a urethra. In addition, the glans and corona may be well defined and the entire clitoris may project somewhat from the body. A woman can have a large clitoris at birth, or acquire one as the result of taking prescription and non-prescription steroids.

The early development of the female sexual and reproductive organs is more like a caterpillar becoming a butterfly than a sapling becoming a tree [1][2]. That is, a microscopic clitoris, urethra, and vagina don't simply grow into larger ones, but rather there is at first significant morphing of basic structure. The following images allow us to see how the position of the vagina migrates along the urethra during early fetal development, as well as observe the early development of the voluntary urethral sphincter. This may explain why the position of the urethral orifice varies in relation of the vaginal orifice.

Female Fetus Uretha Development 12th Week

Female Fetus Uretha Development 14th Week

Female Fetus Uretha Development 18th Week

In these 3D illustrations we can see how the location of the vaginal orifice (pink) migrates along the urethra (red) during early fetal development. The development of the voluntary (striated) urethral sphincter muscle (blue) is also shown. This muscle partially encircles the urethra, being displaced by connective tissue (trigonal plate) along its junction with the vagina. In the young, this muscle extends down along the sides of the vagina. The size and placement of the sphincter muscle varies between individuals, and changes with age. One example of a 54 year old woman, who was most likely post menopausal, indicates the muscle no longer extends down alongside the vagina later in life. [1][3]

The first image shown below details the stages of development for the female external genitals. The second image shows both the development of and similarities between the male and female external genitals.

The full size image downloads in 4 sections: Section 1 Section 2 Section 3 Section 4. From the book Pictorial Human Embryology, Page 48, By Stephen G. Gilbert, Copyright 1989 by the University of Washington Press.

The following illustrations show the development of both the internal and external female sexual and reproductive organs.

Some interesting computer generated 3D images of the developing reproductive and sexual organs are available on this website: http://www.endotext.org

References:

1. The Anatomical Components of Urinary Continence, Christian Wallner A, Noshir F. Dabhoiwala B, Marco C. DeRuiter c, Wouter H. Lamers, European Urology Volume 55, issue 4, pages 761-1002, April 2009

2. Neural Supply to the Clitoris: Immunohistochemical Study with Three-Dimensional Reconstruction of Cavernous Nerve, Spongious Nerve, and Dorsal Clitoris Nerve in Human Fetus, David Moszkowicz, MD, Bayan Alsaid, MD, Thomas Bessede, MD, Mazen Zaitouna, MD, Christophe Penna, MD, Gérard Benoit, MD, and Frédérique Peschaud, MD, J Sex Med 2011;8:1112–1122

3. Fetal Development of the Female External Urinary Sphincter Comples: An Anatomical and Histological Study, Philippe Sebe, Helga Fritsch, Josef Oswald, Christian Schwentner, Andreas Lunacek, Georg Bartsch, Christian Radmayr, The Journal of Urology Volume 173, Issue 5, May 2005, Pages 1738–1742