MALE ENDOCRINOLOGY
(Figure10-1 to 10-3)
A. Glands and their respective hormones
1)
Hypothalamic hormone: GnRH
2)
Anterior pituitary: LH and FSH
3)
Testes: Testosterone, estradiol, and inhibin
-
Testosterone is synthesized by the Leydig cells and estradiol and inhibin by
the Sertoli cells
-
There is no surge center in the hypothalamus of the male and
the GnRH tonic center discharges GnRH in a pulsatile manner to stimulate LH and
FSH
B. Hormones Functions
1) LH (glycoprotein):
- Acts on the Leydig cells and stimulates
the production of testosterone
-
Some testosterone is transported across the basement membrane into the Sertoli
cells and some testosterone also goes into systemic circulation
2) FSH (glycoprotein)
- Acts on
the Sertoli cells to stimulate spermatogenesis and Sertoli cell
function
-
In the Sertoli cells is responsible for activation of aromatase enzyme for
conversion of testosterone into estradiol. If FSH is reduced then Sertoli cell
function and spermatogenesis will be impaired
3) Testosterone (steroid)
In the Sertoli cells:
-
Is bound by androgen binding protein and taken into the lumen of the
seminiferous tubule, for transport to the epididymis
-
Is converted into estradiol by aromatase enzyme and crosses the basement
membrane and goes into circulation
In systemic circulation:
Testosterone
and estradiol feedback upon the hypothalamus causing a slow down in the release
of GnRH, which results in a reduced output of FSH and LH
4) Inhibin
(glycoprotein)
The
sertoli cells also produce inhibin, which negatively feeds back on the anterior
pituitary to selectively suppress FSH.
No comments