Testosterone

When someone mentions testosterone, it might conjure up images of a burly alpha male.

That’s because testosterone, the primary male hormone, is an androgen, andro meaning male and gen meaning “to produce”, which means testosterone helps generate the characteristics associated with male sexuality.

The effects of testosterone are first seen in the fetus.

During the first six weeks of development, the reproductive tissues of males and females are identical,

but in week seven, genes in the sex-determining region of the Y chromosome initiate the development of testicles.

Once they form, the fetal testicles secrete testosterone which guides development of the male urogenital tract and external genitalia,

as well as testicular descent through the inguinal canal which happens in the last two months of fetal development.

The fetal ovaries also secrete testosterone but at much lower levels, and this largely explains the differences in fetal development between boys and girls.

In puberty, the hypothalamic-pituitary axis takes center stage in regulating testosterone levels and gonadal function - which are the testes in young men.

The hypothalamus secretes gonadotropin-releasing hormone which moves through the bridge between the hypothalamus and the pituitary gland, called the hypothalamo-hypophyseal portal system, and gets to the anterior lobe of the pituitary.

In response, the anterior pituitary secretes luteinizing hormone and follicle-stimulating hormone - two gonadotropic hormones which get secreted into the blood and reach the gonads.