Page 295 - Veterinary Histology of Domestic Mammals and Birds, 5th Edition

Male reproductive system (organa genitalia masculina) 277

Arteries and veins ramify within the tunica albuginea Species variation
VetBooks.ir to form a vascular layer (tunica vasculosa). This is located Horse and cat: Interstitial cells contain glycogen.
superficially in the dog and ram, and more deeply in the
Ox: Interstitial cells have mitochondria with folded cris-
stallion and boar. Smooth muscle fibres are also present in
the stallion, boar and ram. tae, as well as those with a tubular cristal morphology.
Connective tissue septa (septula testis) radiate from Rough ER is also present. Light intercalated cells have
the tunica albuginea into the interior of the organ where been observed in the loose connective tissue. These are
they form the mediastinum testis. In ruminants, pigs and presumed to regulate androgen production by adjacent
dogs, the mediastinum testis begins near the extremitas Leydig cells through paracrine pathways.
caudata, extends axially through the testis and recombines
with the tunica albuginea at the head of the epididymis. Parenchyma
The septula testis divide the testicular parenchyma into The tightly wound convoluted seminiferous tubules
numerous pyramidal lobules (lobuli testis), each contain- (tubuli seminiferi convoluti) lie between the septula tes-
ing between two and five convoluted seminiferous tubules tis. Before entering the mediastinum testis, the convoluted
(tubuli seminiferi convoluti). These tortuous tubules tubules straighten to form the straight testicular tubules
are surrounded by loose connective tissue, containing which are joined to the rete testis within the mediastinum.
vascular and nerve plexuses and interstitial cells (hormone- The rete testis empties via the ductuli efferentes testis
producing Leydig cells). into the epididymis (Figures 13.2 and 13.3).

Interstitial cells (Leydig cells) Convoluted seminiferous tubules (tubuli
Leydig cells are found in clusters or cords (Figures 13.4 seminiferi convoluti)
and 13.5). Their number varies with age and species. The The convoluted seminiferous tubules are surrounded by
proportion of total testis volume represented by Leydig a lamina propria. The innermost layer of the lamina pro-
cells is 20–30% in the stallion and boar, and 5% in the pria is in contact with the basal lamina of the seminiferous
bull. Individual cells are connected by gap junctions. Most tubules. Fine collagen and elastic fibres are condensed

individual cells lie adjacent to a capillary. into a thin layer that encloses the so-called peritubular
The interstitial cells are acidophilic and irregularly contractile cells. These cells contain actin bundles and
polyhedral. The nucleus is spherical and euchromatic act as myofibroblasts, bringing about contraction of the
with a prominent nucleolus. Numerous lipid vacuoles, lys- seminiferous tubules. This facilitates spermiation (release
osomes and peroxisomes are present in the pale cytoplasm. of spermatozoa into the tubular lumen) and transport of
Interstitial cells are characterised by large amounts of spermatozoa through the tubules.
smooth ER and abundant, typically elongated mitochon- The tubules are around 50–80 cm long and have a
dria with tubular projections of the inner membrane. diameter of 150–300 μm. Formation of male gametes
This tubular mitochondrial morphology is related to the (spermatogenesis) takes place in the spermatogenic epithe-
endocrine function of the cell. The smooth ER contains lium lining the tubular wall. The epithelium is composed of:
17-β-hydroxysteroid dehydrogenase, which catalyses
the transformation of androstenedione into testoster- · spermatogenic cells and
one. In the mitochondria, cholesterol is converted into · sustentacular cells (Sertoli cells, epitheliocyti
pregnenolone. sustentantes).
Production of androgens (testosterone) by interstitial
cells is stimulated by luteinising hormone (LH) produced SPERMATOGENIC CELLS (CELLULAE
by the hypophysis. Over 90% of the testosterone in the SPERMATOGENICAE)
body is produced by these interstitial testicular cells. The spermatogenic cells of the tubular (spermatogenic)
Testosterone regulates spermatogenesis (together with epithelium differentiate from primordial germ cells that
follicle-stimulating hormone, FSH), sexual behaviour, have migrated into the gonads during embryonic develop-
accessory gland function, development of secondary sex- ment. The spermatogenic cells are located between the
ual characteristics and anabolism. Secretion of testosterone sustentacular cells. Spermatogenic cells undergo several
is subject to negative feedback mechanisms involving the phases of division and maturation before being released
hypothalamus and hypophysis. Interstitial cells also syn- as male gametes (spermatozoa) into the lumen of the
thesise peptides that act through paracrine or autocrine seminiferous tubules. Final maturation occurs during the
(regulation of protein metabolism) mechanisms. passage of the cells through the reproductive apparatus.
The ability to fertilise an ovum is achieved after capaci-
tation takes place within the female reproductive tract.
Multiplication and differentiation of spermatogenic cells

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