A Day in the Life of the Epididymis

Posted on by Paul Turek, MD

The epididymis has been on my mind recently. The Epi-WHAT-amus? What is that? Well, for one, it’s probably the shortest 5-syllable word you’ve ever heard. And, it happens to be the name of an organ that can spell the difference between being a fertile or infertile guy.

The epididymis is an 18-foot long, tightly coiled, almost microscopic, sperm-filled tubule that could fit into a pen cap. It sits on top of, and wraps behind, the testicle. Sperm pass from the testicle into the epididymis and, over about 12 days, get rubbed, shined and gassed up for the big day. At the end of this trip, sperm are ready to fly, prepared to meet an egg, anywhere, anytime. However, until ejaculation occurs, some 200 million sperm are kept in check within the epididymis just waiting to be set free.

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Sperm Maturation

Sounds funny, but passage of sperm through the epididymis is a lot like going through puberty. A lot of serious functionality is acquired during this time that prepares sperm for the real world. Here is a short list of what happens to sperm in the epididymis:

  • Improved structural rigidity that helps with motility or movement.
  • Acquire the ability to move purposefully.
  • Learn to “smell” (chemosense) the fluid released during female ovulation. This helps them know where to go once ejaculated.
  • Acquire the ability to fertilize eggs.

The epididymis is also a “filter” that sorts out and destroys sperm that, for some biological reason, do not pass muster. This activity is increased several hundred-fold after a vasectomy when sperm fills the epididymis with nowhere else to go because of the downstream roadblock.

So, much like the inconspicuous, nerdy guy in the back of the class, the epididymis, in its own quiet way, is critical for normal male fertility. Beware though, that it can also be a problem child. Here’s how:

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