This presentation describe organisation of testes with emphasis on the seminiferous tubules, sertoli cells and Leydig cells. it describe the physiological actions of the Testis and role of Androgen binding protein (ABP) and Inhibin in male reproduction. Neurendocrine control of testicular functions (Gn RH regulation, FSH- effects on germinal epitheluim, LH-effects on Leydig cells, negative feed back regulation) are also described.

1. Fish Reproduction & Conservation Biol. Res. Lab.
Department of Zoology
H.N.B. Garhwal University Campus Badshahithaul
Tehri Garhwal –249199, Uttarakhand, INDIA
e-mail: agarwalnareshk3@rediffmail.com
Dr. N. K. Agarwal
Professor of Zoology
The Testes: Organisation & Physiological
Function
Androgen binding protein (ABP), Inhibin. Neurendocrine control of
testicular functions (Gn RH regulation, FSH- effects on germinal
epitheluim, LH-effects on Leydig cells, negative feed back regulation).

2. The Testes: Organisation & physiological
actions
Androgen binding protein (ABP),
Inhibin.
Neurendocrine control of testicular functions
(Gn RH regulation, FSH- effects on germinal epitheluim,LH-
effects on Leydig cells, negative feed back regulation).

3. Organisation: Human testis with genital duct system
It includes tubuli recti, rete testis, ductuli efferentes, ductus epididymidis
and ductus deferens

4. Section through Testis

5. Part of seminiferous lobule showing
spermatogenic cells and sertoli cells

6. • At all stages of
differentiation, the
spermatogenic cells are in
close contact with Sertoli
cells which are thought to
provide structural and
metabolic support to the
developing sperm cells.
Sertoli cells
•A single Sertoli cell extends
from the basement membrane
to the lumen of the
seminiferous tubule, although
the cytoplasmic processes
are difficult to distinguish at
the light microscopic level.

7. Testosterone is needed in very high quantities
for maintenance of the reproductive tract, and
ABP allows a much higher level of fertility
Sertoli cells serve a number of functions during
spermatogenesis, they support the developing gametes in
the following ways:
•Phagocytose residual cytoplasm left over from spermiogenesis
•They release Antimullerian hormone which prevents formation of the
Mullerian Duct / Oviduct.
•Maintain the environment necessary for development and maturation
via the blood-testis barrier
•Secrete substances initiating meiosis
•Secrete supporting testicular fluid
•Secrete androgen-binding protein, which
concentrates testosterone in close proximity
to the developing gametes
•Secrete hormones effecting pituitary gland control of
spermatogenesis, particularly the polypeptide hormone, inhibin

8. Androgen-binding protein (ABP)
• Androgen-binding protein (ABP) is a glycoprotein (beta-globulin)
produced by the Sertoli cells in the seminiferous tubules of
the testis that binds specifically
to testosterone (T), dihydrotestosterone (DHT), and 17-beta-estradiol.
• Because ABP binds to T and DHT, these hormones are made less
lipophilic and become concentrated within the luminal fluid of the
seminiferous tubules. The higher levels of these hormones
enable spermatogenesis in the seminiferous tubules and sperm
maturation in the epididymis.
• ABP has the same amino acid sequence as sex hormone-binding
globulin (SHBG); the difference is the site of production and the addition
of different sugar moieties. ABP contains 403 amino acids, resulting in
a molecular weight of 44,533. Its gene is located on chromosome 17.
• ABP’s production is regulated under influence of FSH on Sertoli cell,
enhanced by insulin, retinol, and testosterone.

9. Inhibin
Inhibin has been defined as a gonadal hormone that exerts a specific
negative feedback action on the secretion of FSH from the
gonadotropic cells of the pituitary gland.
The existence of inhibin was postulated as early as 1923. However,
only after reliable and sensitive bioassay systems for the detection
and estimation of inhibin had been developed and an ample source
of inhibin was found in the form of ovarian follicular fluid .
It is apparent now that inhibin, which itself consists of a dimer of two
different subunits, alpha and beta, is a member of a much larger
family of (glyco)protein hormones and growth factors, which also
includes Müllerian-inhibiting substance, transforming growth factor-
beta, erythroid differentiation factor, an insect protein that plays an
important role in differentiation, and the dimer of two inhibin beta-
subunits, activin. The latter substance was reported to counteract
the effects of inhibin in pituitary cells. Interactions between these
regulatory substances will certainly be a field of major interest in the
near future. Inhibin molecules, similar to those in the gonads, have
been detected in placental tissue as well.

10. Inhibin
The postulate of inhibin in seminal plasma, prostate, and gastric juice is
apparently due to detection of substances that differ from gonadal
inhibin. Most likely these substances, the amino acid sequences of
which have been elucidated, have a biological function that differs
from the suppression of peripheral levels of FSH in vivo.
Inhibin is produced in the Sertoli cells in the testis and in the granulosa
cells in the ovary.
The production of inhibin is stimulated by FSH, but presently a lot of
controversy exists about other factors that might play a role in the
regulation of the production of inhibin. Because of the lack of reliable
methods for estimation of peripheral levels of inhibin in humans and
experimental animals, almost all evidence for the physiological
importance of inhibin in the regulation of reproductive processes is
derived from circumstantial evidence.
From these indirect results, it appears likely that inhibin plays an
important role in the feedback regulation of peripheral concentrations
of FSH during the period in which Sertoli cells and granulosa cells, the
target cells for FSH, divide, i.e., during puberty in male animals and
during the development of ovarian follicles in female animals.

11. • Hormonal control of spermatogenesis varies among
species.
• In humans initiation of spermatogenesis occurs at
puberty due to the interaction of the Hypothalamus,
Pituitary gland and Leydig cells.
• Follicle stimulating hormone stimulates both the
production of ABP (Androgen Binding Protein) by
Sertoli cells, and the formation of the blood-testis
barrier.
• Androgen binding protein is essential to
concentrating testosterone in levels high enough to
initiate and maintain spermatogenesis, which can be
20-50 times higher than the concentration found in
blood.
Hormonal Control of Testicular function

12. • Follicle stimulating hormone may initiate the
sequestering of testosterone in the testes, but once
developed only testosterone is required to maintain
spermatogenesis. However, increasing the levels of
follicle stimulating hormone will increase the
production of spermatozoa by preventing the
apoptosis of type A spermatogonia.
• The hormone inhibin acts to decrease the levels of
follicle stimulating hormone.
• The Sertoli cells themselves mediate parts of
spermatogenesis though hormone production. They
are capable of producing the hormones estradiol and
inhibin.
• The Leydig cells are also capable of producing
estradiol in addition to their main product testosterone
Hormonal Control of Testicular function

13. Neuro-
Endocrine
control of
testicular
function
(Gn RH regulation,
FSH- effects on
germinal
epitheluim, LH-
effects on Leydig
cells, negative feed
back regulation)

14. March 25, 2020
Prof. N.K.Agarwal
agarwalnareshk3@rediffmail.com