Sex hormones in humans

Testosterone, produced in the testes, is responsible for the development of secondary sexual characteristics in males. Examples include growth of facial and body hair, deepening of the voice, increased muscle mass, and sperm production.

Oestrogen, mainly produced by the ovaries, stimulates the development of secondary sexual characteristics in females. Examples include breast development, widening of the hips, and the start of the menstrual cycle.

The ovaries are the site of egg maturation and release (ovulation). Follicle-stimulating hormone (FSH) stimulates follicle development, leading to oestrogen production. Luteinizing hormone (LH) triggers ovulation.

The uterine lining (endometrium) thickens in preparation for implantation of a fertilized egg. If fertilization does not occur, the lining breaks down and is shed during menstruation.

During the menstrual cycle, oestrogen is primarily produced by the developing follicle in the ovary before ovulation. After ovulation, both oestrogen and progesterone are produced by the corpus luteum in the ovary.

During pregnancy, oestrogen and progesterone are initially produced by the corpus luteum. Later in pregnancy, the placenta becomes the primary source of both hormones, maintaining the uterine lining.

FSH (Follicle-Stimulating Hormone), released by the pituitary gland, stimulates the development of follicles in the ovary. This growth leads to the production of oestrogen, which then influences the uterine lining.

LH (Luteinizing Hormone), released by the pituitary gland, triggers ovulation (the release of an egg from the ovary). It also stimulates the formation of the corpus luteum, which produces progesterone.

Oestrogen, produced by the developing follicle, causes the uterine lining to thicken. A surge in oestrogen stimulates the release of LH, triggering ovulation. It also inhibits further FSH release.

Progesterone, produced by the corpus luteum, maintains the thickened uterine lining, preparing it for implantation. During pregnancy, progesterone prevents the uterus from contracting, thus avoiding miscarriage.