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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.
It is innervated by a variety of nerve endings, although of the the sympathetic innveration dominates. Adrenergic junctions (those which release noradrenaline) are found in the smooth muscle layers. Cholinergic synapses and vasoactive intestinal peptide synapses are found in the connective tissue of the Mucous membrane.
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.
The vas deferens has the greatest muscle-to-lumen ratio of any hollow organ.
The sperm are transferred from each vas deferens into the urethra, partially mixing with secretions from the male accessory sex glands such as the , prostate gland and the bulbourethral glands, which form the bulk of semen.
It has been used:
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 (, , and ), 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 , which release sperm directly into the body cavity, and then into the surrounding water through a simple opening in the body wall.
==Additional images==
Anatomical relations
Within the spermatic cord, the vas deferens is situated posterior (and parallel to) the vessels of the spermatic cord.
Histology
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).
Function
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 epithelial sodium channel ENaC is strongly expressed in smooth muscle cells of the vas deferens. It has been suggested that ENaC functions as a mechanosensor in vascular smooth muscle cells that initiate pressure‐induced constriction known as the "myogenic response". Ion channels ENaC and CFTR, aquaporin of type AQP9 are localized on the apical border of the epithelia. Thus, these channels are involved concurrently in the regulation of fluid and electrolyte balance in the lumen 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.
Other animals
Most vertebrates have some form of duct to transfer the sperm from the testis to the urethra. In cartilaginous fish and , sperm are carried through the archinephric duct, which also partially helps to transport urine from the kidneys. In , there is a distinct sperm duct, separate from the , and often called the vas deferens, although probably not truly homologous with that in humans. The vas deferens loops over the ureter in , but not in Marsupial.
See also
External links
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