Endocrine Functions Of Testis

Male sex hormones are called the androgens. Testis secretes three androgens:

  1. Testosterone
  2. Dihydrotestosterone
  3. Androstenedione.


Among these three androgens, testosterone is secreted in large quantities. However, dihydrotestosterone is more active.

The Sertoli cells of seminiferous cells secrete a hormone called inhibin which inhibits secretion of follicular stimulating hormone from pituitary (see above). But it does not possess any androgenic action.

Source of Secretion of Androgens
The androgens are secreted in large quantities by testes and, by adrenal cortex in small quantities.

Testes
In testes, the androgens are secreted by the interstitial cells of Leydig which form 20% of mass of adult testis. Leydig cells are numerous in newborn male infant and in adult male after puberty. But in childhood, these cells are scanty or non-existing. So, the androgens are secreted in newborn babies and after puberty.

Adrenal cortex
Zona reticularis of adrenal cortex also secretes andro¬gens called testosterone, androstenedione and dehydro-epiandrosterone. The adrenal androgens do not have any significant physiological actions because of their small quantity. In abnormal conditions, the hypersecretion of adrenal androgens results in sexual disorders.

Chemistry
Androgens are steroid hormones synthesized from choles-terol. Androgens are also synthesized directly from acetate. Testosterone is a C19 steroid.

Synthesis
The synthesis of male sex hormones is given in Fig.

Transport
Two thirds of testosterone is transported in plasma by a 3 globulin called gonadal steroid binding globulin or sex steroid binding globulin. The remaining one third is transported by albumin. The plasma level of testosterone in an adult male is 0.4-0.8 ug/dl.