Sex steroids and growth hormones trigger the growth spurt of puberty. For males, the primary steroid hormone responsible is testosterone; for females, it is estradiol.
This growth spurt typically begins around the age of 11 for boys and 9 for girls, and it ends at 13.5 years and 11.5 years respectively. In this stage, both height and weight increase. A growth spurt is only one of a number of physical changes that occur during puberty, a process that matures a child's body, preparing it for sexual reproduction.
Puberty begins when the hypothalamus in the brain emits pulses of Gonadotropin-releasing hormone, or GnRH. These pulses signal the pituitary gland to release hormones that cause the ovaries or testes to produce estradiol and testosterone. As these hormone levels rise, physical changes begin to occur; however, it may take one to two years before these changes are visible.
Along with testosterone and estradiol, there are seven other hormones that cause the many physical changes of puberty. For girls, these changes include not only growth spurts, but also breast development, the growth of pubic and armpit hair, menstruation and ovulation. Boys experience enlargement of the testicles and penis, the growth of pubic and armpit hair, a deepening of the voice, an increase in muscle size and the growth of facial hair.