Puberty: mind and body.

Puberty is the attainment of fertility -- the ability to reproduce. It occurs because our brains begin to secrete one key hormone, gonadotropin-releasing hormone. This causes the pituitary gland to induce maturation of the testis and the ovary, which then produce sex steroid hormones and mature sperm and eggs. We should be concerned that the age at which puberty begins is decreasing in many countries. Puberty starts when adequate growth and energy storage has occurred, so the earlier age of puberty may reflect recent increases in adolescent obesity resulting from more sedentary lifestyles.