Gonads (ovaries in females and testes in males) are both exocrine as well as endocrine in function. Besides producing gametes (ova and sperms), the gonads also secrete sex hormones from sexual maturity to control reproductive activities and maintains reproductive organs.
Ovaries are located in the pelvic cavity in close proximity to the oviducts and uterus. They secrete three female sex hormones namely- oestrogens, progesterone and relaxin.
These are a group of steroid hormone mainly secreted by follicular epithelial cells of the Graafian follicle (ovarian follicle) surrounding the maturing ovum of the ovary. Estradiol is the principal feminizing hormone. It stimulates the development of the female secondary sexual characters during puberty and maintains them through the reproductive years of life. It stimulates the growth and normal functioning of female sex organs like oviducts, uterus, vagina etc. They also stimulate the differentiation of ova (Oogenesis) in the ovaries.
The secretion of oestrogen from the Graafian follicular cells is stimulated by FSH from the anterior lobe of the pituitary gland. Rise of blood- oestrogen level exercises negative feedback control for the secretion of oestrogens.
It is a steroid hormone secreted by the corpus luteum which is an emptied enlarged Graafian follicle in the form of a yellowish body. A Graafian follicle is emptied after the release of ovum from it. Progesterone is released under the influence of LH of the anterior pituitary gland in the second half of the menstrual cycle. Progesterone causes routine temporary changes in the endometrial lining of the uterus and helps in ovulation. During pregnancy, it helps in the implantation of an embryo, development of the placenta, maintenance of pregnancy and growth of secretory alveoli in mammary glands.
It is a proteinous hormone secreted by the corpus luteum only during the later stage of pregnancy. It helps to soften ligaments, especially those of pubic symphysis thus facilitates parturition. It may also affect other ligaments. For example- it affects a women’s foot ligaments, she may experience an increase in shoe size following pregnancy.
A pair of testes is situated in the scrotum of a male. The endocrine part of the testis is formed of groups of cells called Interstitial cells or Leydig’s cells, scattered in the connective tissue between the sperm-producing seminiferous tubules. Interstitial cells are stimulated to secrete male sex hormone called androgens by ICSH of anterior pituitary by a feedback mechanism. The principal androgen is testosterone.
At the time of puberty, testosterone causes the development of male secondary sex organs like seminal vesicle, prostate, scrotum, penis etc. It causes the development of external or accessory male sex characters like beard, moustaches, masculine voice, body hair, comb and wattles in Cock. It also determines the male sexual behaviour and the sex urge. Testosterone stimulates spermatogenesis– formation of sperms and maturation of sperms. It also increases the fertilizing power of sperms. It stimulates erythropoiesis.
The failure of secretion of testosterone in male causes eunuchoidism, where there is reduced secondary sexual characters and failure of spermatogenesis.