Corpus: Epididymal duct

The epididymal duct is the main component of the epididymis and is part of the seminal ducts of the male reproductive organs. The maturation of sperm takes place in it.

The epididymal duct begins in the caput of the epididymis, where it is connected to the rete testis of the testis via the efferent ducts. As it progresses, it runs along the side of the testicle like an elongated ball, forming the body (corpus) of the epididymis. It finally ends in the cauda, where it flows into the ductus deferens without any recognisable transition. When unfolded, the epididymal duct is about 5-6 metres long in adults.

The epididymal duct is lined by a double-row cylindrical epithelium with stereocilia. The lumen filled with spermatozoa is regularly bordered. The high endothelial main cells possess an apical proton pump to keep the milieu acidic and thus inhibit the motility of the spermatozoa. They reabsorb fluid and produce so-called epididymosomes for the maturation of the spermatozoa. The subepithelial connective tissue contains circular myofibroblasts in the caput and corpus, and smooth muscle cells in the caudal part. The muscle layer becomes thicker from proximal to distal, while the epithelium becomes thinner.

After their production in the testicles, the sperm enter the epididymal duct via the efferent ducts and are transported onwards towards the vas deferens. The sperm cells need an average of 12-14 days to reach the cauda by contracting the myofibroblasts from the caput of the epididymis. During this process, they are in close contact with the cylindrical epithelium of the epididymal duct, which controls the maturation process of the sperm by secreting epididymosomes containing glycoproteins. This maturation process changes their morphological and functional characteristics:

• The sperm head becomes smaller and more compact due to condensation of DNA.
• The cytoplasm of the sperm is further reduced, which slims down their shape.
• The sperm cells acquire the ability to motility.
• The structure of the cell membrane is changed so that they acquire the capacity for capacitation and acrosomal reaction.

Once these maturation steps have been completed, the sperm are ready for ejaculation and collect in the caudal part of the epididymis, where they are stored.