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The vas deferens (Latin: "carrying-away vessel"; plural: vasa deferentia), also called ductus deferens (Latin: "carrying-away duct"; plural: ductus deferentes), is part of the male reproductive system of many vertebrates; these ducts transport sperm from the epididymis to the ejaculatory ducts in anticipation of ejaculation. It is a partially coiled tube which exits the abdominal cavity through the inguinal canal.
Vertical section of the testis, to show
the arrangement of the ducts
|Artery||Superior vesical artery, artery of the ductus deferens|
|Lymph||External iliac lymph nodes, internal iliac lymph nodes|
|Latin||Vas deferens (plural: vasa deferentia),|
Ductus deferens (plural: ductus deferentes)
There are two ducts, connecting the left and right epididymis with the seminal vesicles to form the ejaculatory duct in order to move sperm. In humans, each tube is about 30 centimeters (1 ft) long, 3 to 5 mm (0.118 to 0.197 inches) in diameter and is muscular (surrounded by smooth muscle). Its epithelium is pseudostratified columnar epithelium lined by stereocilia.
The vas deferens is supplied by an accompanying artery (artery of vas deferens). This artery normally arises from the superior (sometimes inferior) vesical artery, a branch of the internal iliac artery.
During ejaculation, the smooth muscle in the walls of the vas deferens contracts reflexively, thus propelling the sperm forward. This is also known as peristalsis. The sperm is transferred from each vas deferens into the urethra, partially mixing with secretions from the male accessory sex glands such as the seminal vesicles, prostate gland and the bulbourethral glands, which form the bulk of semen.
The procedure of deferentectomy, also known as a vasectomy, is a method of contraception in which the vasa deferentia are permanently cut, though in some cases it can be reversed. A modern variation, which is also known as a vasectomy even though it does not include cutting the vas, involves injecting an obstructive material into the ductus to block the flow of sperm.
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), microsurgical epididymal sperm aspiration (MESA), or other methods of collecting sperm cells directly from the testicle or epididymis.
Uses in pharmacology and physiologyEdit
It has been used:
- as a bioassay for the discovery of enkephalins, the endogenous opiates.
- to demonstrate quantal transmission from sympathetic nerve terminals.
- as the first direct measure of free Ca2+ concentration in a postganglionic nerve terminal.
- to develop an optical method for monitoring packeted transmission (similar to quantal transmission).
Most vertebrates have some form of duct to transfer the sperm from the testes to the urethra. In cartilaginous fish and amphibians, sperm is carried through the archinephric duct, which also partially helps to transport urine from the kidneys. In teleosts, there is a distinct sperm duct, separate from the ureters, and often called the vas deferens, although probably not truly homologous with that in humans. The vas deferens loops over the ureter in placental mammals, but not in marsupial mammals.
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.
In amniotes, 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.
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.
- Dr C Sharath Kumar, Ph D Thesis, University of Mysore, 2013
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- Brain, K. L.; Bennett, M. R. (1997). "Calcium in sympathetic varicosities of mouse vas deferens during facilitation, augmentation and autoinhibition". The Journal of Physiology. 502 (3): 521–36. doi:10.1111/j.1469-7793.1997.521bj.x. PMC 1159525. PMID 9279805.
- Brain, K. L.; Jackson, V. M.; Trout, S. J.; Cunnane, T. C. (2002). "Intermittent ATP release from nerve terminals elicits focal smooth muscle Ca2+ transients in mouse vas deferens". The Journal of Physiology. 541 (Pt 3): 849–62. doi:10.1113/jphysiol.2002.019612. PMC 2290369. PMID 12068045.
- Romer, Alfred Sherwood; Parsons, Thomas S. (1977). The Vertebrate Body. Philadelphia, PA: Holt-Saunders International. pp. 393–395. ISBN 978-0-03-910284-5.
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- Patricia J. Armati; Chris R. Dickman; Ian D. Hume (17 August 2006). Marsupials. Cambridge University Press. ISBN 978-1-139-45742-2.
|Wikimedia Commons has media related to Vas deferens.|
- Anatomy photo:36:07-0301 at the SUNY Downstate Medical Center—"Inguinal Region, Scrotum and Testes: Layers of the Spermatic Cord"
- Anatomy photo:44:02-0301 at the SUNY Downstate Medical Center—"The Male Pelvis: Distribution of the Peritoneum in the Male Pelvis"
- MedicalMnemonics.com: 2424 319 [dead link]
- Cross section image: pelvis/pelvis-e12-15—Plastination Laboratory at the Medical University of Vienna
- inguinalregion at The Anatomy Lesson by Wesley Norman (Georgetown University) (testes)