The epididymis

Each testis has an epididymis lying over its dorsal aspect. The tail of the epididymis (joined to the vas deferens) is situated at the caudal end of the testis and the head (joined to the rete testis) is situated at the cranial end. The epididymis consists of long, highly convoluted tubules measuring up to 45 m

Cross Section The Epididymis

external cremaster muscle

Fig. 3.11. Transverse cross-section through the inguinal canal area of the stallion.

external cremaster muscle

Fig. 3.11. Transverse cross-section through the inguinal canal area of the stallion.

in length and weighing in the order of 25 g each in a mature stallion (Thompson, 1992). They originate from the rete testis as a series of tubules which, over the length of the epididymis, converge to form one single tube continuous with the vas deferens.

The epididymis can be divided into three sections. This may be done on the basis of anatomy; that is, on epithelial cell characteristics - namely, the caput or head, the corpus or body, and the caudal or tail end of the epididymis; or alternatively, on the basis of function - namely, the initial (part of the efferent ducts plus the initial part of the caput), the middle (remainder of the caput plus the corpus) and the terminal (cauda plus the proximal vas deferens). The caudal end of the epididymis lies caudal to the testis, forming the characteristic projection seen on the exterior of the scrotum when viewed in the live animal. It is this caudal end that joins with the vas deferens and, as the terminal section, it is the major site of spermatozoan storage, providing storage for between 53% and 62% of the extra-gonadal spermatozoa reserves in sexually active and rested stallions, respectively (Gebauer et al., 1974a; Amann et al., 1979a). The middle epididymis is responsible primarily for spermatozoan maturation and is the likely site for the secretion of androgen-dependent protein maturation factors enabling sperm to undergo capacitation within the female tract in readiness for fertilization (Merkies and Buhr, 1998); it is also likely to be the site of initiation of spermatozoa progressive motility (Johnson et al., 1980; Setchell, 1991). The initial epididymis is primarily the site for fluid and solute reabsorption and resultant concentration of spermatozoa in readiness for emission.

Throughout the length of the epididymis, the epithelial cell lining of the lumen is highly folded with additional microvilli, thus significantly increasing the surface area available for storage of spermatozoa and for fluid reabsorption (Fig. 3.12). The tubules are surrounded by a well innervated smooth muscle layer which is involved in epididymal contraction and which is increasingly obvious as the cauda end is approached (Setchell and Brooks, 1988).

In order for maturation to occur, spermatozoa need to remain within the epididymis for up to 7 days. Those that are subsequently not ejaculated are reabsorbed, ensuring a continual supply of fresh spermatozoa (Gebauer et al., 1974a,b,c; Thompson et al., 1979a). In general, mammalian epididymal fluid contains significant concentrations of glycerylphosphorylcholine, glycosidases, amino acids, androgen-dependent proteins, potassium, inositol, carnitine, dihydrotestosterone, and alkaline and acidic phosphatases. The specific concentration of these elements has not yet been ascertained in horses, but it is likely that equine epididymal fluid contains similar components (Rossdale and Ricketts, 1980; Setchell, 1991). Spermatozoa spend 4-5 days moving through the epididymis by means of muscle contraction of the epididymal walls and hydrostatic pressure. Spermatozoa can be stored in the caudal epididymis for between 2 days and several weeks. The storage capacity of the cauda is 10 X 109; storage capacities of the caput and corpus epididymis are much smaller, at 12 and 17 X 106, respectively (Samper, 1995a).

Cross Section EpididymusSertoli Cells
Fig. 3.12. Cross-section through the (a) cauda and (b) caput epididymis. Note the differences in the epithelial cell lining of the lumen, which is highly ciliated in the caput region, and the increased thickness in muscle wall in the cauda epididymis.

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  • Dina
    Are sertoli cells in the epidydimis?
    5 years ago

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