Vas Deferens: Anatomy and Function of the Ductus Deferens

Image of vas deferens definition in dictionary

The vas deferens are a pair of long, muscular tubes that extend from the epididymis to the pelvic cavity at the level of the bladder. During ejaculation, sperm are transported by the vas deferens from the epididymis through the urethra and out of the body.

Also known as the ductus deferens, the vas deferens are a vital part of male reproductive system and male fertility. The vas deferens are the tubes that are cut when undergoing a vasectomy, which is a surgical procedure for male sterilization that prevents sperm from leaving the body.

Chart depicting anatomy of the male reproductive system.

Structure

The vas deferens appear as a pair of thick, muscular tubes. The tubes are identical to each other, measuring approximately 12 inches (30 cm) in length.(1) These vas deferens branch off from the spermatic cord, which also contains blood vessels and a system of nerve fibers wrapped in connective tissue.

The vas deferens start at the epididymis, where sperm is collected after it has been produced in the testes. The vas deferens run from the epididymis into the pelvic area to just behind the bladder.

These two tubes then branch off, forming two ampullae that are attached to the bladder’s left and right walls. These ampullae serve as storage receptacles for semen, eventually connecting with the ejaculatory ducts and then to the urethra.(2)

The vas deferens are composed of three layers:

  • The Adventitia – The outermost layer of connective tissue
  • The Muscular Coat – made up of different layers of muscle fibers, lies beneath the adventitia.
  • The Mucous Coat – The innermost layer, lined with columnar epithelial cells.(3)

It is possible to born without the vas deferens. Although rare, this condition causes infertility. A congenital absence of vas deferens may occur without a known cause, but it is frequently linked with another genetic condition known as cystic fibrosis.

Although males born with an absence of vas deferens are usually infertile, the condition doesn’t affect sex drive or the capability to have sex 3 Some men born without vas deferens are still able to father children with the help of assisted reproductive technology.(4)

Function of the Vas Deferens

The main purpose of the vas-deferens is to transport sperm (in Latin, the term vas-deferens translates as “carrying-away vessel”). The testes produce sperm and it is then transferred to the epididymis.

This structure, which looks like a coiled tube, stores sperm until it matures. When the penis becomes erect, it signals the sperm cells to leave the epididymis and move into the vas deferens.(5)

The vas deferens pushes the sperm forward through muscular contractions. As sperm cells reach the ampullae they are joined with seminal fluid from the seminal vesicle. The seminal fluid is pushed from the ampullae through the ejaculatory ducts, past the prostate gland, where it is mixed with a milky secretion.

Finally, the entire mixture (ejaculate) exits the body through to the urethra.


References:

  1. https://en.wikipedia.org/wiki/Vas_deferens
  2. https://www.britannica.com/science/ductus-deferens
  3. https://www.imaios.com/en/e-Anatomy/Anatomical-Parts/Vas-deferens
  4. https://medlineplus.gov/genetics/condition/congenital-bilateral-absence-of-the-vas-deferens/#genes
  5. https://medlineplus.gov/ency/anatomyvideos/000121.htm
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