Page 308 - Veterinary Histology of Domestic Mammals and Birds, 5th Edition

290 Veterinary Histology of Domestic Mammals and Birds

bolic activity changes. While they remain in the epididymal didymis of birds has no subdivisions. Ductuli efferentes
VetBooks.ir duct, however, motility of the spermatozoa is limited by emerging from the testis enter the epididymis along its entire
the acid environment. Changes also occur on the surface length. The epithelium of the ductules is simple columnar.
of the cell membrane and there is an increase in negative The proximal efferent ductules narrow to form distal effer-
charge. The localisation of glycoprotein receptors in the ent ductules (ductuli efferentes distales) (approximately 70
post-acrosomal region is important for facilitating con- in the cock). These empty via connecting ductules (ductuli
tact between spermatozoa and the zona pellucida of the conjugentes) into the epididymal duct.
oocyte. The epididymal duct (ductus epididymidis) is lined
Towards the end of the maturation process, the sper- by pseudostratified epithelium with stereocilia. It is sur-
matozoon loses the cytoplasmic droplet (remnant of rounded by loose connective tissue invested with smooth
spermiogenesis). Failure of this process renders spermato- muscle cells (Figures 13.21 and 13.22). Throughout its
zoa infertile. Mature spermatozoa are subsequently stored course, the epididymal duct gradually increases in thick-
for some time in the tail of the epididymis. ness. At the caudal pole of the epididymis it opens into the
deferent duct.
Pampiniform plexus
Through its histological structure, and its anatomical Ductus deferens
association with the loops of the testicular artery, the The ductus deferens extends from the epididymal duct to
pampiniform plexus serves primarily to facilitate heat the pelvic urethra. The gently coiled initial portion lies
exchange. These features also promote the diffusion of on the medial side of the testis. From the testis, the duc-
gases, low-molecular weight substances, adrenalin, nor- tus deferens passes within the spermatic cord (funiculus
adrenalin, serotonin and lipid-soluble substances such as spermaticus), together with the testicular artery and vein,
prostaglandins and steroid hormones. lymphatic vessels and sympathetic nerves. In the pelvic
Anastomoses between the larger veins of the plexus cavity, the left and right deferent ducts pass into the plica
markedly reduce the rate of blood flow. This vasoreg- urogenitalis. The section within this fold comprises the
ulatory mechanism is augmented by adventitial and pars glandularis of the ductus deferens. In the stallion,
intramural portal systems in the centre of the plexus. bull and dog, this portion is expanded to form an ampulla
(ampulla ductus deferentis) (see below).
Epididymis of birds
The epididymis of the chicken lies against the dorsome- Species variation
dial surface of the testis. It extends along approximately Horse and ox: Shortly before the urethra, the ductus
two-thirds of the testicular border. Unlike the mammalian deferens merges with the ductus excretorius of the
epididymis, which consists of a head, body and tail, the epi- vesicular glands to form the ductus ejaculatorius.

13.21 Ductus epididymidis (cock). Haematoxylin and 13.22 Ductus epididymidis (drake). Haematoxylin and
eosin stain (x275). eosin stain (x275).

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