epididymis

The epididymis is a coiled, muscular tube that lies along the posterior border of the testis within the scrotum. It serves as the first part of the male reproductive tract after the efferent ducts and connects to the vas deferens. The organ is divided into three regions: the caput (head) at the superior aspect, the corpus (body) in the middle, and the cauda (tail) at the inferior end, with sperm passing sequentially through these segments during maturation and storage.

Histologically, the epididymis is lined by a pseudostratified columnar epithelium with tall stereocilia and several cell types, including principal and basal cells. The underlying lamina propria contains a dense smooth muscle layer that facilitates peristaltic movement of sperm. The epithelium is highly involved in modifying the luminal fluid by absorbing fluid and secreting proteins and enzymes, creating a microenvironment that supports sperm maturation and storage.

Functionally, the epididymis is essential for sperm maturation, enabling the acquisition of motility and fertilizing capability as sperm transit through its length, particularly in the caput and corpus. It also concentrates sperm by reabsorbing most of the tubular fluid and stores mature sperm in the cauda until ejaculation. The organ is actively peristaltic and responds to neural and hormonal signals.

Clinically, the epididymis can be affected by infections (epididymitis), obstruction, congenital anomalies, or injury, all of which can impact fertility. It is typically evaluated in the broader context of male reproductive health and may be involved in procedures such as vasectomy.