The epididymis (; : epididymides or ) is an elongated tubular genital organ attached to the posterior side of each one of the two male reproductive glands, the testicles. It is a single, narrow, tightly coiled tube in adult humans, in length; uncoiled, the tube would be approximately 6 m (20 feet) long. It connects the testicle to the vas deferens in the male reproductive system. The epididymis serves as an interconnection between the multiple efferent ducts at the rear of a testicle (proximally), and the vas deferens (distally). Its primary function is the storage, maturation, and transport of sperm cells.

Structure

The human epididymis is situated posterior and somewhat lateral to the testis. The epididymis is invested completely by the tunica vaginalis (which is continuous with the tunica vaginalis covering the testis).

The epididymis can be divided into three main regions:

  • The head (). The head of the epididymis receives spermatozoa via the efferent ducts of the mediastinum of the testis It is involved in absorbing fluid to make the sperm more concentrated. The concentration of the sperm here is dilute.
  • The body (). This has an intermediate epithelium and smooth muscle thickness. The stereocilia are much shorter in the cauda (tail) segment.

Stereocilia

The stereocilia of the epididymis are long cytoplasmic projections that have an actin filament backbone. During their transit in the epididymis, sperm undergo maturation processes necessary for them to acquire motility and fertility. Final maturation (capacitation) is completed in the female reproductive tract.

The epididymis secretes immobilin, a large glycoprotein that is responsible for creating the viscoelastic luminal environment that serves to mechanically immobilize spermatozoa until ejaculation. Immobilin is predominantly secreted into the proximal caput epididymidis before the acquisition of the potential for sperm motility.

During emission, sperm flow from the cauda epididymis (which functions as a storage reservoir) into the vas deferens where they are propelled by the peristaltic action of muscle layers in the wall of the vas deferens, and are mixed with the diluting fluids of the prostate, seminal vesicles, and other accessory glands before ejaculation (forming semen).

Contrary to popular belief, sperm are capable of causing a pregnancy even without ever travelling through the epididymis. This has been proven in two cases in the United States in the 1980s where a couple of men's vasa deferentia were directly surgically attached to their efferent ducts and these men both subsequently impregnated their partners within the next couple of years. The antioxidant proteins produced include catalase, glutathione peroxidases, glutathione-S-transferases, peroxiredoxins, superoxide dismutases, thioredoxin reductase and thioredoxins.

In reptiles, there is an additional canal between the testis and the head of the epididymis, which receives the various efferent ducts. This is, however, absent in all birds and mammals.

<gallery>

Image:Illu repdt male.jpg|Human male reproductive system

Image:Illu testis 1b.jpg|Testis

Image:Mesorchium.svg|Schematic drawing: cross-section through a testicle

Image:Epididymis high mag.jpg|Micrograph of epididymis - H&E stain

Image:Epididymis.JPG|Micrograph

File:Slide4UMR.JPG|Deep dissection of epididymis

</gallery>[https://commons.m.wikimedia.org/wiki/File:Epididymal_head,_with_measurement,_longitudinal_view.png]

See also

  • Epididymis evolution from reptiles to mammals
  • List of distinct cell types in the adult human body

Notes