Epididymis

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The epididymis is a crescent-shaped organ and an essential component of the male reproductive system. It lies in close proximity to the testis, positioned along its superior and posterior surfaces. Functionally, it is a site of sperm storage and maturation until the time of discharge to the ductus deferens (vas deferens).

The epididymis consists of the efferent ductules and the duct of the epididymis as well as associated vessels, smooth muscles and coverings of connective tissue. Structurally, the epididymis is divided into a head, a body and a tail, with the efferent ductules occupying the head and the duct of the epididymis forming its body and tail.

Both the efferent ductules and duct of epididymis are covered with pseudostratified columnar epithelium. Two types of cells can be found here, principal and basal cells:

• Principal cells are the most abundant cells in the epididymal epithelium and play a major role in secretion and absorption. A special type of long microvilli called stereocilia extend from the luminal surface of the principal cells, which aid in the absorption of luminal fluids by increasing the surface area of the principal cells.
• Basal cells are found on the basal lamina and assist in maintaining the structural integrity of the blood-epididymis barrier.

Additionally, halo cells, a type of lymphocytes, reside throughout the epididymal epithelium and serve as the primary immune cells in the epididymis.

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