How Vasectomies Work

The Science of Vasectomy

The male reproductive system
The male reproductive system
©2004 HowStuffWorks

During sexual reproduction, a man's body ejaculates, or discharges, sperm into a woman's body in an attempt to create a pregnancy. To understand how vasectomy works you'll first need to understand the mechanics of ejaculation.

  • Two testicles, which are housed in the scrota, produce millions of sperm.
  • Sperm then wait in two nearby tubes, known as the epididymides, where they develop and mature.
  • Once they have reached maturity, the sperm are carried from each epididymis into two longer tubes called the vas deferens, which connect to the prostate.
  • The vas deferens and seminal vesicles work together to carry millions of mature sperm out through the head of the penis via a lubricative, sugary liquid called semen.
  • Before and during sexual intercourse, the penis fills with blood, stiffens and typically remains hard until a man climaxes and has an orgasm.
  • During orgasm, the semen, carrying the sperm, is ejaculated out of the penis through the urethra.

[sources: WebMD, American Urological Association Foundation].

When a man has a vasectomy, both of the vas deferens are cut, blocked or tied to prevent his sperm from traveling out through the urethra during sex. However, a vasectomy does not work immediately. Because sperm are continuously being created in the testicles, housed in the epididymides and carried towards the urethra, it can take several months for existing sperm to completely clean out of the reproductive system. During this time another form of birth control must be used to prevent pregnancy [source: Davis]. After vasectomy, there should be no noticeable change in semen quality or quantity. The testicles will continue to produce sperm after vasectomy, where they are absorbed by the body and vanish over time [source: National Library of Medicine].