alt=3D Medical Illustration showing vas deferens.|thumb|304x304px|3D medical illustration showing vas deferens.
The vas deferens (: vasa deferentia), ductus deferens (: ductūs deferentes), or sperm duct is part of the male reproductive system of many vertebrates. In mammals, spermatozoa are produced in the seminiferous tubules and flow into the epididymal duct. The end of the epididymis is connected to the vas deferens. The vas deferens ends with an opening into the ejaculatory duct at a point where the duct of the seminal vesicle also joins the ejaculatory duct.
The vas deferens is a partially coiled tube which exits the abdominal cavity through the inguinal canal.
Etymology
Vas deferens is Latin, meaning "carrying-away vessel" while ductus deferens, also Latin, means "carrying-away duct".
Structure
The human vas deferens measures 30–35 cm in length, and 2–3 mm in diameter. It is continuous proximally with the tail of the epididymis, Together they form part of the spermatic cord.
Blood supply
The vasa deferentia are supplied with blood by accompanying arteries, the (arteries of vas deferens). These arteries normally arises from the superior (sometimes inferior) vesical arteries, a branch of the internal iliac arteries.
Innervation
The vas deferens receives innervation from an autonomic plexus of post-ganglionic sympathetic fibres derived from the inferior hypogastric plexus. Cholinergic synapses and vasoactive intestinal peptide synapses are found in the connective tissue of the mucosa.
Anatomical relations
Within the spermatic cord, the vas deferens is situated posterior (and parallel to) the vessels of the spermatic cord.
The vas deferens has the greatest muscle-to-lumen ratio of any hollow organ. The epithelial sodium channel ENaC is strongly expressed in smooth muscle cells of the vas deferens.
Clinical significance
Damage to the vas deferens during inguinal hernia repair may cause infertility.
Contraception
A vasectomy 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.
Disease
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).
Uses in pharmacology and physiology
The vas deferens has a dense sympathetic innervation, making it a useful system for studying sympathetic nerve function and for studying drugs that modify neurotransmission.
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 Ca<sup>2+</sup> concentration in a postganglionic nerve terminal.
- to develop an optical method for monitoring packeted transmission (similar to quantal transmission).
Other animals
Most vertebrates have some form of duct to transfer the sperm from the testes to the urethra. In cartilaginous fish and amphibians, sperm are 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.