Puberty is the term for the hormonal, physical and cognitive changes that bring children into adulthood. It is caused by changes in the secretion of the master reproductive hormone called gonadotropin releasing hormone -- or GnRH - which triggers a cascade of hormonal changes. Some of the common first signs of puberty include breast budding in girls and growth of the testes in boys, followed by the appearance of pubic hair and a growth spurt.
The first signs of puberty are hormonal changes, but you would not be aware of them without special blood tests. In girls and boys, puberty is driven by the onset of rhythmic releases of high levels of the hormone GnRH from the hypothalamus of the brain. This pattern of GnRH secretion causes nighttime peaks of secretion of the gonadotropin (gonad-growing) hormones, follicle-stimulating hormone (FSH) and luteinizing hormone (LH) from the pituitary gland. Nightime peaks of LH and FSH occur only during early puberty and only during sleep, so it is critical for pre-teens and teens to sleep enough and sleep deeply.
In girls, LH and FSH cause the ovaries to make higher levels of estrogen. The levels of FSH rise first at about ages 9 to 10 followed by LH. Estrogen levels begin to rise steeply at about age 10 to 11. In boys, LH is the predominant hormone and it stimulates the testes to secrete testosterone. Testosterone levels begin to rise at about age 12 and steadily increase during the next 2 years. Estrogen and testosterone drive most of the later pubertal changes.
Physical pubertal changes are broken into discrete phases measured by a clinical evaluation called Tanner staging. Tanner stage 1 equates to pre-puberty. At Tanner stage 2, you begin to see the first physical changes. For girls, the first obvious sign of puberty is a slight swelling of the breasts called breast budding. Breast budding occurs when estrogen levels rise at about ages 10 to 11. For boys, the first obvious sign of puberty is growth of the testes at about 8 to 9 years of age. Also in Tanner stage 2, girls and boys sprout their first pubic hairs. In girls, pubic hair appears at about age11 due to androgens from the adrenal gland; in boys, pubic hairs appear at 11 to12 years of age.
In Tanner stage 1, pre-puberty, you can expect a child to grow about 5 to 6cm per year. For girls in Tanner Stage 2 -- about age 11 -- this increases to 7 to 8cm per year. Girls continue to grow at that rate until growth stops at about age 16. Boys do not begin to grow more quickly until Tanner stage 3 at about 12 to 13 years. Boys’ growth peaks at Tanner stage 4 -- about age 14 -- at a rate of 10cm per year and ends at age 17. Growing taller results from the actions of growth hormone, which your child is secreting during sleep. In stages of accelerated growth, a child can literally grow overnight.