They develop from the mesoderm of the embryo.
The gonads are the sex glands; the ovaries and the testes. They produce ova and sperms respectively i.e. cytogenic in nature but also secrete hormones.
(a) OVARIES. The hormones produced by the ovaries include oestrogens, progesterone, relaxin and inhibinlactin. (i) Oestrogens. These are secreted by the cells of Graafian (ovarian) follicles.
It stimulates the development of female secondary sex characteristics during puberty and maintains them through the reproductive years of adult life. It also stimulates maturation of ova (in the ovaries) and development of the uterine epithelium and the mammary glands.
(ii) Progesterone. It is secreted by the corpus luteum of the ovary.
It stimulates further development of the uterine epithelium and mammary glands. It is also required for the formation of the placenta and for the maintenance of pregnancy. Both estradiol and progesterone are required for ovulation.
(iii) Relaxin. It is secreted by the corpus luteum only during the later stages of pregnancy and helps to soften ligaments, especially those that hold the pubic symphysis together.
It may also affect other ligamets, e.g., if it affects a woman's foot ligaments, she may experience an increase in shoe size following pregnancy.
(iv) Inhibinlactin. Inhibinlactin is secreted by the corpus luteum. Inhibin hormone inhibits and actin hormone activates the FSH and GnRH production.
A pair of testes is situated in the scrotum of male. The connective tissue present between the seminiferous tubules in a testis contain small clusters of endocrine cells called interstitial cells or Leydig's cells.
These cells secrete various male sex - hormones called androgens. The principal androgen is testosterone.