MALE ENDOCRINOLOGY

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(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.