The vas deferens (pl.: vasa deferentia), with the more modern name ductus deferens (pl.: ductūs deferentes), is part of the male reproductive system of many vertebrates. The ducts transport sperm from the epididymides to the ejaculatory ducts in anticipation of ejaculation. The vas deferens is a partially coiled tube which exits the abdominal cavity through the inguinal canal.
The human vas deferens measures 30–35 cm in length, and 2–3 mm in diameter.[2]: 1297 It is continuous proximally with the tail of the epididymis,[2]: 1296 and exhibits a tortuous, convoluted initial/proximal section (which measures 2–3 cm in length). Distally, it forms a dilated and tortuous segment termed the ampulla of vas deferens before ending[2]: 1297 by uniting with a duct of the seminal vesicle to form the ejaculatory duct.[3] Together they form part of the spermatic cord.[4]
The vas deferens receives innervation from an autonomic plexus of post-ganglionic sympathetic fibres derived from the inferior hypogastric plexus.[2]: 1297
Within the spermatic cord, the vas deferens is situated posterior (and parallel to) the vessels of the spermatic cord.[2]: 1297
The vas deferens traverses the inguinal canal to reach the pelvic cavity; it enters the pelvic cavity lateral to the inferior epigastric vessels. At the deep inguinal ring, the vas deferens diverges from the testicular vessels to pass medially to reach the base of the prostate posteriorly.[2]: 1297
The vas deferens consists of an external adventitial sheath containing blood vessels and nerves, a muscular middle layer composed of three layers of smooth muscle (with a circular muscle layer interposed between two longitudinal muscle layers), and an internal mucosal lining consisting of pseudostratified columnar epithelium (which bears the non-motile stereocilia).[2]: 1297 [9]
The vas deferens has the greatest muscle-to-lumen ratio of any hollow organ.[2]: 1297
Avasectomy is a method of contraception in which the vasa deferentia are permanently cut. In some cases, it can be reversed. A modern variation, vas-occlusive contraception, involves injecting an obstructive material into the ductus to block the flow of sperm.[12]
The vas deferens may be obstructed, or it may be completely absent in a condition known as congenital absence of the vas deferens (CAVD, a potential feature of cystic fibrosis), causing male infertility. Acquired obstructions can occur due to infections. To treat these causes of male infertility, sperm can be harvested by testicular sperm extraction (TESE) or microsurgical epididymal sperm aspiration (MESA).[13]
The vas deferens has a dense sympathetic innervation,[14] making it a useful system for studying sympathetic nerve function and for studying drugs that modify neurotransmission.[6]
It has been used:
as a bioassay for the discovery of enkephalins, the endogenous opiates.[15]
to demonstrate quantal transmission from sympathetic nerve terminals.[16]
as the first direct measure of free Ca2+ concentration in a postganglionic nerve terminal.[17]
to develop an optical method for monitoring packeted transmission (similar to quantal transmission).[18]
In cartilaginous fishes, the part of the archinephric duct closest to the testis is coiled up to form an epididymis. Below this are a number of small glands secreting components of the seminal fluid. The final portion of the duct also receives ducts from the kidneys in most species.[19]
Inamniotes, however, the archinephric duct has become a true vas deferens, and is used only for conducting sperm, never urine. As in cartilaginous fish, the upper part of the duct forms the epididymis. In many species, the vas deferens ends in a small sac for storing sperm.[19]
The only vertebrates to lack any structure resembling a vas deferens are the primitive jawless fishes, which release sperm directly into the body cavity, and then into the surrounding water through a simple opening in the body wall.[19]
^Gonzales, GF (December 2001). "Function of seminal vesicles and their role on male fertility". Asian Journal of Andrology. 3 (4): 251–8. PMID11753468.
^ abBurnstock, G; Verkhratsky, A (2010). "Vas deferens--a model used to establish sympathetic cotransmission". Trends in Pharmacological Sciences. 31 (3): 131–9. doi:10.1016/j.tips.2009.12.002. PMID20074819.
^Hughes, J; Smith, T. W.; Kosterlitz, H. W.; Fothergill, L. A.; Morgan, B. A.; Morris, H. R. (1975). "Identification of two related pentapeptides from the brain with potent opiate agonist activity". Nature. 258 (5536): 577–80. Bibcode:1975Natur.258..577H. doi:10.1038/258577a0. PMID1207728. S2CID95411.
^ abcdRomer, Alfred Sherwood; Parsons, Thomas S. (1977). The Vertebrate Body. Philadelphia, PA: Holt-Saunders International. pp. 393–395. ISBN978-0-03-910284-5.