A long time ago, in an uterus far, far away, there was a sexually undifferentiated embryo, that could develop into either a male or a female according to its sex chromosomes.
During that time, most of its organs and systems took shape and started functioning.
But one system - the reproductive system - developed and then waited for a trigger to kick into action.
Even though we’re born with differentiated, male or female, sex organs, it’s not until puberty that they fully mature. That’s when an individual becomes capable of reproduction.
Sexual maturation is under the control of the hypothalamic-pituitary-gonadal axis.
The hypothalamic-pituitary-gonadal axis is a system of hormone signaling between the hypothalamus, pituitary gland, and gonads, either the testes or ovaries, to control sexual development and reproduction.
Gonadotropin-releasing hormone, or GnRH is released into the hypophyseal portal system, which is a network of capillaries connecting the hypothalamus to the hypophysis - or pituitary.
When gonadotropin-releasing hormone reach the anterior lobe of the pituitary gland, it stimulates cells called gonadotrophs, to release gonadotropin hormones: luteinizing hormone, or LH, and follicle-stimulating hormone, or FSH, into the blood.
These gonadotropin hormones then stimulate the gonads to produce sex specific hormones - which are estrogen and progesterone in females, and testosterone in males.
Now, the amount of hormone that gets produced by this axis varies over a person’s lifetime, and that affects the development of the sex organs, as well as the appearance of secondary sexual characteristics.