The epididymis is part of the human male reproductive system and is present in all mammals. It is a narrow, tightly-coiled tube connecting the efferent ducts from the rear of each testicle to its vas deferens. The epididymis can be divided into three main regions, the head (caput), body (corpus) and tail (cauda). Sperm formed in the testis enter the caput epididymis, progress to the corpus, and finally reach the cauda region, where they are stored. Sperm entering the caput epididymis are incomplete - they lack the ability to swim forward (motility) and to fertilize an egg. During their transit in the epididymis, sperm undergo maturation processes necessary for them to acquire these functions. Sperm maturation is completed in the female reproductive tract (capacitation).

During ejaculation, sperm flow from the lower portion of the epididymis (which functions as a storage reservoir). They are packed so tightly that they are unable to swim, but are transported via the peristaltic action of muscle layers within the vas deferens, and are mixed with the diluting fluids of the seminal vesicles and other accessory glands prior to ejaculation (forming semen).

Inflammation of the epididymis is called epididymitis.

A Gartner's duct is a homologous remnant in the female.

References

• Jones RC. 1999. To store or mature spermatozoa? The primary role of the epididymis. International Journal of Andrology 22:57-67. abstract