Genital humps

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Sex development in the embryonic phase

The genital tubercle or genital eminence ( genital tubercle ) is common for both sexes conditioning the clitoris or of the penis in mammals . It arises from a strong increase in cells (overgrowth) of the mesenchyme on the head and abdomen ( cranioventral ) of the cloacal membrane . The genital hump elongates into a protophallus , which is initially the same length in both sexes. The urogenital groove ( sulcus urogenitalis ) is formed on the underside of the phallus and is bounded by the two urogenital folds ( plicae urogenitales ) on the left and right. On the side of the genital protuberance, the sex bulges develop - in turn, the common abutment of the scrotum or the outer labia for both sexes .

Progressive differentiation in humans

Sex differentiation in humans

In humans, gender differentiation begins to develop towards a clear and thus separating design ( differentiation ) of the external genitalia around the ninth week of embryonic development ( pregnancy ).

Female development

In female embryos, the protophallus of the genital protuberance remains short and develops into the clitoris. The urogenital folds remain separate and form the inner labia.

Male development

In male embryos , after the sixth week, the so-called SRY gene is read on the Y chromosome and a protein is formed that is known as the testicular-determining factor (HDF). As a transcription factor, this protein regulates the expression of numerous other genes in the genome and initiates gender differentiation. Under this influence, there is a remodeling of the internal sex organs (especially the paired testicles , epididymis , spermatic ducts and the prostate gland ). It also stimulates certain somatic cells to develop into testosterone-producing Leydig cells . After the start of testosterone production there around the seventh week, this androgen is converted to dihydrotestosterone (DHT) in the target cells ( urogenital sinus / genital tubercle ) with the help of the enzyme steroid 5α-reductase (SRD5) .

Under the influence of this DHT, the most biologically active form of testosterone, the external genitalia begins to develop : the protophallus of the genital cusp elongates to a penis ( phallus ), the urogenital groove closes to the spongiosa of the urethra and forms the erectile tissue of the urethra . From the central part of the phallus, the penile cavernous body and, in other animals, the penis bones develop .

See also

literature

  • Bertram Schnorr, Monika Kressin: Embryology of Pets. 5th edition. Enke, Stuttgart 2006, ISBN 3-8304-1061-1 .
  • Alfred Sigel, RH Ringert: Pediatric urology. 2nd, completely revised edition. Springer, Berlin / Heidelberg a. a. 2001, ISBN 978-3-540-64764-5 , Chapter 1: Embryology of the urogenital tract ( full text ).
  • Julianne Imperato-Mcginley, Vivian Sobel, Yuan-Shan Zhu: Fetal hormones and sexual differentiation. In: Obstetrics and Gynecology Clinics of North America. Volume 31, No. 4, January 2005, pp. 837-856, doi: 10.1016 / j.ogc.2004.08.005 ( full text ).

Individual evidence

  1. ^ German Ethics Council: Intersexuality - Opinion. ( Memento of the original from March 18, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF) Berlin, February 23, 2012, ISBN 978-3-941957-27-5 , pp. 30–31. @1@ 2Template: Webachiv / IABot / www.ethikrat.org
  2. ↑ Serge Nef, Luis F. Parada1: Hormones in male sexual development. In: Genes & Development. 2014, Volume 14, pp. 3075-3086, doi: 10.1101 / gad.843800 .
  3. ↑ a b Hey-Joo Kang, Julianne Imperato-McGinley, Yuan-Shan Zhu, Zev Rosenwaks: The effect of 5α-reductase-2 deficiency on human fertility. In: Fertility and sterility. Volume 101, No. 2, January 2014, pp. 310-316, doi: 10.1016 / j.fertnstert.2013.11.128 ( full text ).
  4. ↑ Figure: Illustration of the role of testosterone and dihydrotestosterone in the sex differentiation of a male embryo. At: marlin-prod.literatumonline.com ; accessed on February 23, 2019.
  5. ↑ Julianne Imperato-McGinley, Yuan-Shan Zhu: Androgens and male physiology - The syndrome of 5 alpha-reductase-2 deficiency. In: Molecular and Cellular Endocrinology. Volume 19, No. 1, December 2002, pp. 51-59, doi: 10.1016 / S0303-7207 (02) 00368-4 ( full text ).