Page 302 - Veterinary Histology of Domestic Mammals and Birds, 5th Edition

284 Veterinary Histology of Domestic Mammals and Birds

stage of germ cells are referred to as segments. The sum after their discoverer Enrico Sertoli (1842–1910), as Sertoli
VetBooks.ir of all segments along the length of the tubule constitutes a cells.
spermatogenic wave.
In adult, sexually active mammals, columnar susten-
Characteristic cell associations arise from generations tacular cells (70–80 μm high) extend from the basement
of cells in different states of differentiation. The cycle of membrane to the tubular lumen. They are pyramidal in
the seminiferous epithelium consists of the recurring shape, tapering towards the lumen from a broad base rest-
sequences of cellular associations at a particular point in ing on the basement membrane. Sustentacular cells lie
the tubule. between the differentiating germ cells with which they are
Based on morphological criteria, the number of stages in structural and functional contact through specialised
of the seminiferous epithelial cycle is not necessarily fixed intercellular connections (Figures 13.11 to 13.13).
(8–16 in the bull, 8 in the ram, 6–8 in the boar and 8 in the The ovoid to ellipsoid nucleus is euchromatic and is
stallion). typically located basally. Under seasonal influences, or dur-
Generally, only one stage of the cycle is visible in a ing sexual quiescence, the nucleus may become displaced
histological cross-section of the tubule (Figures 13.4 to towards the lumen. Migration of the nucleus also occurs
13.6). Except for some irregularities, segments are gener- during certain stages of the seminiferous epithelial cycle.
ally arranged so that they follow the next most developed The nucleolus is reticulated (net-like). In ruminants, the
stage of the cycle. nucleoli are also characteristically multivesicular.
The duration of spermatogenesis is approximately 49 Numerous thin, branching cytoplasmic processes
days in the stallion, 52 days in the bull, 52 days in the ram extend from the lateral walls of the sustentacular cells to
and 34 days in the boar. Final maturation of spermatozoa surround the various stages of spermatogenic cells. These
takes place in the epididymis. contribute actively to trans-epithelial migration of germ
cells and to release of spermatozoa into the tubular lumen
SUSTENTACULAR CELLS (SERTOLI CELLS, (spermiation). The cytoplasm contains a well-developed
EPITHELIOCYTI SUSTENTANTES) Golgi apparatus, numerous mitochondria and, in pigs and
In addition to germ cells, the spermatogenic epithelium ruminants, abundant rough ER. The smooth ER is well
contains somatic cells referred to as sustentacular cells or, developed in all species. Particularly in ruminants, pigs and

Spermatozoa approaching spermiation

Cytoplasm of
sustentacular cell
Cytoplasm of Spermatid (late
sustentacular cell maturation phase)

Spermatid Spermatid
(cap phase) (cap phase)
Spermatid
(acrosome phase) Tubulobulbar
complexes
Spermatid
(Golgi phase)
Primary spermatocyte Primary spermatocyte
with cytoplasmic with cytoplasmic
connection connection
Adluminal
compartment
Junctions between Cytoplasm of a
sustentacular cells sustentacular cell
Endoplasmic reticulum
Basal compartment
Spermatogonium Basement membrane

Nucleus of sustentacular cell
13.11 Sustentacular cell and various stages of spermatogenesis (schematic; based on the bull).

Vet Histology.indb 284 16/07/2019 15:04