Sertoli cells, also known as supporting, or
sustentacular,cells.
The Sertoli cells are important for the
function of the testes.
These cells are elongated pyramidal cells
that partially envelop cells of the spermatogenic lineage. The bases of the
Sertoli cells adhere to the basal lamina, and their apical ends frequently
extend into the lumen of the seminiferous tubule.
In the light microscope, the outlines of
Sertoli cells appear poorly defined because of the numerous lateral processes
that surround spermatogenic cells .
Studies with the
electron microscope reveal that these cells contain abundant smooth endoplasmic
reticulum, some rough endoplasmic reticulum, a well-developed Golgi complex,
and numerous mitochondria and lysosomes. The nucleus, which is often triangular
in outline, possesses numerous infoldings and a prominent nucleolus; it
exhibits little heterochromatin
Adjacent Sertoli cells are bound together by occluding junctions at the
basolateral part of the cell, forming a blood
testis barrier .
The spermatogonia lie
in a basal compartment that is
situated below the barrier. During spermatogenesis, some of the cells resulting
from division of spermatogonia somehow traverse these junctions and come to lie
in the adluminal compartment
situated above the barrier.
Spermatocytes and
spermatids lie within deep invaginations of the lateral and apical margins of
the Sertoli cells, above the barrier. As the flagellar tails of the spermatids
develop, they appear as tufts extending from the apical ends of the Sertoli
cells.
Sertoli cells are also
connected by gap junctions that provide ionic and chemical coupling of the
cells; this may be important in coordinating the cycle of the seminiferous
epithelium described above
Sertoli cells in humans and in other
animals do not divide during the reproductive period. They are extremely
resistant to adverse conditions such as infection, malnutrition, and
x-irradiation and have a much better rate of survival after these insults than
do cells of the spermatogenic lineage.
Sertoli cells have several
functions:
·
Support,
protection, and nutritional regulation of the developing spermatozoa.
As mentioned above, the cells of the spermatogenic series are interconnected
via cytoplasmic bridges. This network of cells is physically supported by
extensive cytoplasmic ramifications of the Sertoli cells. Because spermatocytes,
spermatids, and spermatozoa are isolated from the blood supply by the
blood–testis barrier, these spermatogenic cells depend on the Sertoli cells
to mediate the exchange of nutrients and metabolites. The Sertoli cell barrier
also protects the developing sperm cells from immunological attack (discussed
below).
·
Phagocytosis.
During spermiogenesis, excess spermatid cytoplasm is shed as residual bodies.
These cytoplasmic fragments are phagocytosed and digested by Sertoli cell
lysosomes.
·
Secretion.
Sertoli cells continuously secrete into the seminiferous tubules a fluid that
flows in the direction of the genital ducts and is used for sperm transport.
Secretion of an ABP by Sertoli
cells is under the control of follicle-stimulating hormone (FSH) and
testosterone and serves to concentrate testosterone in the seminiferous tubule,
where it is necessary for spermatogenesis.
·
Sertoli cells can convert
testosterone to estradiol. They also secrete a peptide called inhibin, which suppresses synthesis
and release of FSH in the anterior pituitary gland
·
Production
of the anti-mullerian hormone. Anti- mullerian hormone (AMH, also
called mullerian-inhibiting hormone),
a glycoprotein that is a member of the transforming growth factor-
·
The
blood testis barrier. The existence of a barrier between
the blood and the interior of the seminiferous tubules accounts for the fact
that few substances from the blood are found in the testicular fluid. The
testicular capillaries are fenestrated and permit passage of large molecules.
Spermatogonia have free access to materials found in blood. However, occluding
junctions between the Sertoli cells form a barrier to the transport of large
molecules along the space between Sertoli cells. Thus, the more advanced stages
of spermatogenesis are protected from blood-borne products protecting male germ
cells against blood-borne noxious agents.
·
Production
of inhibin B. Inhibin B inhibits the production
of FSH by the hypophysis.
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