Page 304 - Veterinary Histology of Domestic Mammals and Birds, 5th Edition

286 Veterinary Histology of Domestic Mammals and Birds

germ cells. Cytoplasmic streaming results in the direction Straight testicular tubules
VetBooks.ir spermatozoa into the tubular lumen (spermiation) is a The convoluted seminiferous tubules are continued by
of spermatocytes towards the tubular lumen. Release of (tubuli seminiferi recti)

complex process that commences with dissolution of the short, straight testicular tubules (tubuli seminiferi recti)
tubulobulbar complexes between the sustentacular cell which open into the rete testis. The straight testicular
and the head of the spermatozoon (Figure 13.13). tubules are usually short, though some are elongated in
Secretion of tubular fluid components: Tubular fluid the boar and stallion. In the dog and bull, groups of susten-
is produced in large quantities. Like intracellular fluid, it is tacular cells form a club-shaped intraluminal projection at
rich in potassium. The tubular fluid carries spermatozoa the transition from the convoluted to the straight tubules
through the ductuli efferentes into the ductus epididymidis (terminal segment). These contribute to phagocytosis and
(epididymal duct), where they complete their maturation. prevent retrograde flow of tubular fluid.
Formation of the blood–testis barrier: The blood–tes- The straight testicular tubules are lined with simple
tis barrier separates the circulatory system (blood and cuboidal to columnar resorptive epithelium containing
lymph) and the interior of the convoluted seminiferous lymphocytes and macrophages.
tubules. While in common usage, the term ‘blood–testis
barrier’ is misleading. It consists of the tight seal formed Rete testis
between the plasmalemma of neighbouring sustentacular The rete testis consists of anastomosing straight tubules.
cells by basolateral intercellular junctions. This gives rise These are surrounded by the loose connective tissue and
to two compartments within the tubular epithelium: elastic meshwork of the mediastinum testis, and by myo-
fibroblasts (Figures 13.3 and 13.14). The epithelium of the
· a basal compartment containing spermatogonia and rete testis is simple squamous to columnar. Two epithe-
· an adluminal compartment containing spermato- lial layers are present in the bull. The epithelium is highly
cytes and spermatids (Figure 13.11). secretory and increases the volume of the tubular fluid.
Androgens in the tubular fluid are absorbed across the
In the adluminal compartment, the sustentacular cells epithelium to a limited extent.
provide protection for the spermatocytes and spermatids.
Maintenance of the barrier is important for the secre- Ductuli efferentes testis
tory functions of the sustentacular cells, through which At the extremitas capitata of the testis, the ductuli efferen-
an osmotic gradient is established in the luminal region, ties testis penetrate the tunica albuginea and pass into the
and for maintenance of an optimal environment for sper- head of the epididymis (Figures 13–2 and 13–3 to 13–16).
miogenesis. The vulnerable spermatids are protected from A species-dependent number of ductuli efferentes (stal-
autoimmune reactions, toxins and mutagens. lion 12–23, bull 12–13, boar 14–21, dog 15–16) combines

13.14 Testis (bull). Haematoxylin and eosin stain (x30). 13.15 Ductuli efferentes of the epididymis (stal-
lion). The lumen contains agglutinated spermatozoa.
Haematoxylin and eosin stain (x100).

Vet Histology.indb 286 16/07/2019 15:04