Puberty occurs through a long process and begins with a surge in hormone production, which in turn causes a number of physical changes.
It is the stage of life characterized by the appearance and development of secondary sex characteristics (for example, a deeper voice and larger adam's apple in boys, and development of breasts and more curved and prominent hips in girls) and a strong shift in hormonal balance towards an adult state.
This is triggered by the pituitary gland, which secretes a surge of hormonal agents into the blood stream, initiating a chain reaction to occur.
The male and female gonads are subsequently activated, which puts them into a state of rapid growth and development; the triggered gonads now commence the mass production of the necessary chemicals.
Males experience their growth spurt about two years later, on average, than females.
During their peak height velocity (the time of most rapid growth), adolescents grow at a growth rate nearly identical to that of a toddler—about 4 inches (10.3 cm) a year for males and 3.5 inches (9 cm) for females.
The first places to grow are the extremities—the head, hands and feet—followed by the arms and legs, then the torso and shoulders.
In addition to changes in height, adolescents also experience a significant increase in weight (Marshall, 1978).
The weight gained during adolescence constitutes nearly half of one's adult body weight.
This non-uniform growth is one reason why an adolescent body may seem out of proportion.
During puberty, bones become harder and more brittle.