Descensus testis

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The descent of the testis ( lat. For, testicular descent ') is the majority of fetal movements of the testis of his place of embryonic plant behind the kidney through the inguinal canal into the scrotum ( scrotum ).

mechanism

Normal anatomy after the testicle descends into the scrotum

The testicle arises in the abdomen outside of the peritoneum (extraperitoneally) at the level of the upper lumbar vertebrae in the area of ​​the kidney anlage. Controlled by the anti-Müllerian hormone (AMH, produced by the Sertoli cells ), the testes initially descend to the edge of the pelvis in the transabdominal phase. This section is called transabdominal testicular descent. In the literature, the process that leads to transabdominal descent is described as a balloon-like swelling and shortening of the gubernaculum due to proliferation , which takes the testicle with it. In the subsequent inguinoscrotal phase, the testes descend androgen-mediated ( testosterone increase ) along the gubernaculum testis (the lower gonadal ligament) via the inguinal canal into the scrotum. A funnel-shaped protuberance of the peritoneum forms in the scrotum , the processus vaginalis peritonei. Here a shortening of the gubernaculum by regression seems to play the decisive role. The processus vaginalis also recedes except for a small residue that remains in the scrotum and the scrotum no longer communicates openly with the peritoneal cavity. The gubernaculum testis remains as a testicular ligament ( ligamentum testis proprium ) and epididymal tail ligament ( ligamentum caudae epididymidis ).

Temporal occurrence

In ruminants , the testes descend as early as the third fetal month. In humans and pigs, it is completed around birth. In horses, the testicles migrate through the inguinal canal at birth . In dogs, as in domestic cats, testicular descent is usually only completed at the end of the first month of life, so missing testicles in the scrotum in newborn puppies are not a cause for concern. In rodents , the testes do not descend until puberty and adult animals can still retract the testes into the abdominal cavity.

Disruptions

Disorders of testicular descent ( Maldescensus testis ) are relatively common and presumably of genetic origin. They can affect both or just one testicle. These developmental disorders lead to abnormalities in the position of the testicle such as cryptorchidism or testicular ectopia.

If the testicles remain in the abdominal cavity, no fertile sperm can develop ( infertility ) because the temperature is too high for spermatogenesis. They also tend to form tumors . The chance of developing a testicular tumor in the course of life is 3 to 8 times higher.

Disturbances in the regression of the processus vaginalis peritonei lead to a congenital inguinal hernia .

Mammals without testicular descent

With some mammals (e.g. elephant , many marine mammals, sloth ) there is no testicular descent. With them, the testicles stay in the abdominal cavity and are still able to produce fertile sperm. The animal species without testicular descent are summarized under the term Testiconda .

literature

  • Alfred Benninghoff, Detlev Drenckhahn: Anatomy. 16th edition. Volume 1, Urban & Fischer, Jena / Munich 2003, ISBN 3-437-42340-1 .
  • Bodo Christ, Franz Wachtler: Medical Embryology . Ullstein Medical, Wiesbaden 1998, ISBN 3-86126-163-4 .
  • L. Werdelin, A. Nilsonne: The evolution of the scrotum and testicular descent in mammals: a phylogenetic view. In: J Theor Biol. 196 (1), 1999 Jan 7, pp. 61-72. PMID 9892556

Individual evidence

  1. ↑ Undescended testicles - knowledge for medical professionals. Accessed January 2, 2019 (German).