Vas deferens

Position of the spermatic duct

In male mammals , birds and reptiles, the spermatic duct ( Latin ductus deferens, vas deferens ) connects the epididymis with the urethra on both sides and is used to carry the sperm . As part of the spermatic cord , coming from the epididymis, the spermatic duct runs through the inguinal canal and then runs along the urinary bladder , takes up the duct of the vesicle gland (seminal vesicle, vesicula seminalis ) and then flows into the urethra in the area of the seminal mound .

The surgical ligation of the vas deferens is called a vasectomy and leads to infertility .

histology

Like all internal hollow organs , the vas deferens show the three-layer structure of a “membranous-muscular tube” with an internal mucous membrane , the tunica mucosa , a muscle layer, the tunica muscularis and an externally attached tunica adventitia .

The mucous membrane has longitudinal folds so that a star-shaped lumen is created. There is no submucosa . Depending on the species, the organ delimitation forms a two- to multi-row high prismatic epithelium , which is partially covered with stereocilia , to the lumen . The own layer of the mucous membrane ( lamina propria mucosae ) is characterized by networks of elastic connective tissue fibers that extend into the muscle layer. Glands are only formed near the mouth in the urethra, in the area of the spermatic duct ampoule (see below).

The smooth muscles of the muscle layer are arranged at different angles and thus form spiral tours in the spermatic duct wall. It is extremely dense noradrenergic innervated, which is necessary because of its special transport function of the vas deferens: It transports the sperm suspension from the cauda equina of the epididymis into the urethra .

In the tunica adventitia there are connective tissue, blood vessels - the arteries and venae ductus deferentis - and sympathetic nerve fibers. In the peritoneum , rudiments of Müller's duct can usually be detected, possibly a complete uterus masculinus .

Vas deferens ampoule

In the wall of the end section of the vas deferens gland packs are embedded, which are called glandulae ampullae . In humans and most mammal species (with the exception of tomcats and boars), these glandular deposits also lead to an externally visible expansion of the vas deferens, which is known as the vas deferent ampulla ( Ampulla ductus deferentis ).

A vas deferens ampoule is formed in most vertebrates. It is missing, for example, in the marsupials , whales , manatees , cats and pigs , although glandulae ampullae are usually formed in the wall and these just do not lead to a visible expansion. The spermatic duct ampoule of mammals belongs to the accessory sex glands and forms part of the seminal fluid . In monotones , a seminal vesicle ampoule is present but does not show any secretory activity.

Evolutionary development

The spermatic ducts lead upwards within the male abdomen, over the pubic bone , around the ureters , through the prostate and then into the urethra. This detour is justified in the evolutionary history of vertebrates and thus also of humans. The spermatic duct originally led from the testicles inside the body to the penis . In his book The Lie of Creation , Richard Dawkins cites the complicated path of the vas deferens through the body as evidence for the theory of evolution and against the pseudoscience of intelligent design .

literature

AJP van den Brock: Gonads and ways of execution. In: L. Bolk et al. (Ed.): Handbook of the comparative anatomy of the vertebrates. Volume 6, Urban & Schwarzenberg, Berlin / Vienna 1933, pp. 1–154.
Hans-Georg Liebich: Functional histology of domestic mammals. 4th, completely revised and expanded edition. Schattauer, Stuttgart / New York 2004, ISBN 3-7945-2311-3 .
Uwe Gille: Male sexual organs. In: Franz-Viktor Salomon et al. (Hrsg.): Anatomie für die Tiermedizin. Enke, Stuttgart 2004, ISBN 3-8304-1007-7 , pp. 389-403.
Renate Lüllmann-Rauch: pocket textbook histology. 5th edition. Thieme, Stuttgart / New York 2015, ISBN 978-3-13-129245-2 , pp. 530f.

Individual evidence

^ Richard Dawkins: The Greatest Show on Earth: The Evidence for Evolution. Bantam Press, London 2009, ISBN 978-1-4165-9478-9 , pp. 364-3365.
↑ George C. Williams: Natural selection: domains, levels, and challenges (= Oxford series in ecology and evolution. ). Oxford University Press, New York 1992, ISBN 978-0-19-506933-4 .
↑ Richard Dawkins: The Creation Lie Why Darwin Is Right. Ullstein, Berlin 2010, ISBN 978-3-550-08765-3 . (Original title: The Greatest Show on Earth: The Evidence for Evolution. ).

[1] Richard Dawkins: The Greatest Show on Earth: The Evidence for Evolution. Bantam Press, London 2009, ISBN 978-1-4165-9478-9 , pp. 364-3365.

[2] George C. Williams: Natural selection: domains, levels, and challenges (= Oxford series in ecology and evolution. ). Oxford University Press, New York 1992, ISBN 978-0-19-506933-4 .

[3] Richard Dawkins: The Creation Lie Why Darwin Is Right. Ullstein, Berlin 2010, ISBN 978-3-550-08765-3 . (Original title: The Greatest Show on Earth: The Evidence for Evolution. ).