Epididymis in Animals: Structure and Functions

The epididymis is composed of a single, tortuous, coiled tubule starting from the proximal portion of the testis and is responsible for nutrition, maturation, transport, and storage of spermatozoa.

Structure

Epididymis consists of three parts:

1. Head of the epididymis (or caput): The proximal or spermatic cord end of the epididymis is more or less flat, broad, and U-shaped. It is a fimbricated tubular mass and is hidden due to its enclosure within a fat pad.
2. Body of the epididymis (or corpus): It is the intermediate, narrow part. It is a cylindrical tubular mass and is clearly visible.
3. Tail of the epididymis (or cauda): It is the distal, enlarged end. It is an inverted, triangular tubular mass and is clearly visible. It serves as the storage site for spermatozoa.

The epididymis is covered by a smooth muscle coat, which transports spermatozoa by peristaltic movement. It exhibits greater secretory and absorptive activity.

The epididymal duct provides an environment that enables spermatozoa to gain fertility.

Spermatozoa are removed from the epididymis through periodic contractions of the epididymis and ductus deferens. This results in a gradual trickle of spermatozoa from the tail, through the ductus deferens, into the pelvic urethra, where they are flushed out of the tract during urination. This process allows for the continual removal of sperm from the epididymis.

Grossly, the epididymis appears as an approximately cylindrical organ.

Spermatozoa stored in the epididymis retain fertilizing capacity for several weeks. The cauda epididymis contains about 75% of the total epididymal spermatozoa.

The tail of the epididymis acts as a reservoir of fully mature sperm and becomes turgid with stored sperm in sexually active animals.

The length of the epididymis varies among species: approximately 20 metres in the stallion, 30 metres in the bull, and 50 metres in the boar.

The epididymis is closely attached to the surface of the testis proper by fibrous tissue. It is continuous with the vas deferens.

Functions

• Absorption: Removes excess fluid and degenerating sperm to concentrate viable spermatozoa.
• Secretion: Releases substances essential for sperm maturation and motility.
• Maturation: Enables spermatozoa to gain motility and fertilizing capacity.
• Transportation of sperm: Moves sperm from the testis to the vas deferens via peristaltic contractions.
• Storage of spermatozoa: Stores mature sperm in the tail until ejaculation.