Epididymis: where sperm get fine tuned and functional

June 8, 2012Carole 4 Comments »

In honor of the up-coming Father’s Day, I thought I’d tell the story of a little known but highly significant male reproductive organ- the epididymis. It is pronounced Eppie-Diddy-Mus which may sound like an urban rapper but I assure you, it is not.  The epididymis which is attached to and  lies just above the testicle, is responsible for the “detailing” or “fine-tuning” of freshly made sperm just released from the testicle.  Yes, the testicle produces the sperm but without the polishing and detailing in the epididymis, sperm wouldn’t swim and wouldn’t be able to fertilize an egg. So pretty important,  no?

It is important for a male to be able to tell when there are changes in the size or feel of his testicles or epididymides because these may be signs of cancer or inflammation associated with infection. This link, Get to Know Your Testis, explains how to find the epididymis ( which lies to the top and back of each testicle). You should also be able to also feel the tubes leaving from the epididymis called the vas deferens. If a vasectomy is performed, these tubes which normally carry sperm from the epididymis to the penis are clipped inside the scrotum to render the male sterile. Reconnecting the tubes surgically via a vasectomy-reversal procedure can restore fertility if not too much time has elapsed between the two surgeries.  There are two kinds of vasectomy reversal procedures as described in this article from the NY TImes Health Guide. It’s worth reading for those who want to know more about vasectomy and it’s reversal.

  • Vasovasostomy . The severed ends of the vas deferens are sewn back together.
  • Vasoepididymostomy . The vas deferens is surgically reattached directly to the epididymis. This procedure is more difficult to perform and is used when vasovasostomy cannot be performed or does not work.

But this post is about the epididymis, which despite years of research over many decades is still shrouded in mystery. The epididymis has three functionally distinct regions , the caput (or head), the corpus (or body) and the cauda (or tail). What is clear is that by the time the sperm transits these three regions and is stored in the final region, the cauda, prior to ejaculation, it is a fully mature sperm, capable of strong forward progressive motility and has acquired the molecular ability to fertilize the egg. But in spite of decades of research in both animals and humans, we still don’t fully understand all the molecular changes that occur in the sperm membrane within this organ.

The review article New Insights into Epididymal Biology and Function is a highly detailed review for those who want to understand the nitty-gritty scientific efforts to understand the molecular mechanisms responsible for the epididymides’ unique ability to grant life-giving properties to sperm. For the andrologist or reproductive scientist, it has lots of references for further study.

Up to 40% of infertility is due to male-specific causes. Some of these causes are not obvious and may well be due to molecular sperm defects we are incapable of detecting–and may be due to faulty “fine-tuning” of sperm cells in the epididymis.  Much of male-specific infertility can be addressed by the use of intracytoplasmic sperm injection or ICSI, which bypasses some deficiencies in sperm functionality acquired in the epididymis, like the inability to swim. However, ICSI is not without risks and sometimes fertilization fails even with ICSI so ICSI is not the solution for every cause of male infertility.

The original sperm cell produced by the testis looks like a sperm cell, but it is non-functional and can not swim. That is why testicular sperm can only be used with ICSI, not for conventional IVF or insemination, because it can not yet swim, nor fertilize an egg. The lipid (fat molecules) and proteins that are inserted into the plasma membrane of the sperm cell also change while in transit through the epididymis.  Some molecules are shedded and others are added to the sperm membrane to ultimately produce a functional sperm cell which can swim to, attach to, penetrate and fertilize an egg.

Researchers looking for male contraceptives are also interested in understanding which proteins are involved with functional maturation of sperm so that a reversible non-hormonal method to block sperm maturation can be designed. Likewise, if the molecular maturation mechanisms were understood, it might be possible to mature sperm in vitro and be able to use conventional in vitro fertilization, instead of ICSI, to gain the benefit of some natural selection. Therefore, a better understanding of the epididymis may lead to new therapies for infertility as well as new methods for contraception.

Each segment of the epididymis appears to have distinct gene profiles, producing a highly regulated cellular micro-environment, capable of responding to signalling pathways in a highly orchestrated way. Each segment is physiologically separated from the adjacent segment by connective tissue, permitting compartmentalization of the organ and segment-specific regulation . Not surprisingly, the various cells of the epididymis respond to androgens, the male hormone. Studies suggest that sperm and the cells lining the epididymis also exchange cell to cell  signals as part of the in transit maturation process and probably further regulate that process. The epididymis may have the most complex fluid composition of any exocrine gland and this composition varies with each region of  epididymis. The caput produces 70-80% of the proteins secreted into the epididymal lumen. By the time the sperm get to the cauda end, most of the fluid has been reabsorbed, fundamentally increasing the concentration of proteins bathing the sperm in the tubes.

Take good care of your epididymis and it will take good care of you.  Check your epididymis (and testicles) every month for changes in size, areas of hardening or changes in sensitivity or pain. Let your physician know about any unusual changes which could indicate epididymal (or testicular) inflammation, infection, presence of cysts or nodules,  or even cancer, all of which can impair your fertility and overall health. Here’s a link to more information on how to do a self-exam.

Happy Father’s Day!



© 2012 – 2015, Carole. All rights reserved.

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