Gonads — Testis and Ovary

The gonads — the paired testes in the male and the paired ovaries in the female — are unusual among the organs of the body in serving two quite distinct roles simultaneously. As the primary reproductive organs, they produce the gametes (sperm in the testis, ova in the ovary) required for sexual reproduction. As endocrine glands, they also secrete the sex hormones responsible for the development of the reproductive organs themselves, for the appearance of secondary sexual characters at puberty, and for the ongoing regulation of reproductive physiology through adult life.

In the male, the paired testes lie within the scrotum, outside the main body cavity, an arrangement that keeps them at a slightly lower temperature than core body temperature, favourable for sperm production. Within each testis, two functionally distinct cell populations are of particular endocrine and physiological importance. The interstitial cells of Leydig, scattered in the connective tissue between the sperm-producing seminiferous tubules, secrete the principal male sex hormone, testosterone, under the stimulus of luteinising hormone (LH) from the anterior pituitary. Testosterone is responsible for the development of the male reproductive organs during fetal life, for the appearance of male secondary sexual characters at puberty — including facial and body hair growth, deepening of the voice, and increased muscle mass — and, together with follicle-stimulating hormone (FSH) acting on a second cell type, the Sertoli cells lining the seminiferous tubules, for the ongoing maintenance of spermatogenesis (sperm production) through adult life. The Sertoli cells, besides supporting and nourishing the developing sperm cells directly, also secrete the hormone inhibin, which feeds back to suppress FSH secretion from the pituitary once sperm production is proceeding adequately. …