Puberty is the time in life in which a person becomes sexually mature. On average, in the United States, girls go through puberty from ages 10 to 14 and boys go through it between ages 12 to 16, though some boys and girls may begin earlier or later than those ages. There are some similarities in puberty in girls and boys, but the two sexes generally have different experiences during this time in life.
Similarities Between Boys and Girls
Hair growth is one of the major signs that an adolescent is beginning puberty. Boys and girls will see hair growth in their pubic and armpit regions. Both boys and girls experience a growth spurt beginning at puberty that will take them nearly to their full adult height.
Physical Changes in Boys
Puberty begins in boys when the testes begin producing testosterone, the main sexual hormone in males. The notable physical change in boys, besides growth of hair and overall physical growth, is the enlargement of the penis, testes and scrotum. Sperm production occurs toward the end of puberty. Boys will notice that their voices begin to deepen; this stage is characterized initially by sudden uncontrollable cracks in the voice while speaking.
Physical Changes in Girls
Puberty begins in girls when their ovaries begin producing estrogen and progesterone, the main sexual hormones in females. Female physical growth begins with the growth of breasts, initially called breast budding. The growth spurt will happen around the same time as breast development or just after, followed by the growth of hair in the pubic and axillary regions. The female growth spurt will end earlier in puberty than in boys; girls will also experience a widening of the hips and accumulation of fat on the hips and thighs, though these may not be noticeable on all girls.
Menstruation in Girls
The initial release of an egg from the ovary and failure to fertilize that egg begins with menarche, or a girl's first menstrual period. Most girls will experience menarche about two years after breast budding. The female menstrual cycle averages about 28 days, but may be unpredictable in girls. The cycle begins with the selection of an immature egg and subsequent growth of that egg into maturity. The matured egg will be released from the ovary (this stage is called ovulation). That egg will travel down the fallopian tube and into the uterus where the uterine lining awaits the implantation of a fertilized egg. If the egg is not fertilized (by a male's sperm, resulting in pregnancy), the egg, along with the lining will be shed in the form of blood. Most women lose an average of 30mL of blood during their period.
Brain Development
The brain of an adolescent experiencing puberty is different than it is both prior to and after puberty. A study by JN Giedd and colleagues published in the journal "Nature Neuroscience" in 1999 demonstrated that the brain experiences an increase in the growth of gray matter during the period just before puberty begins, which may be related to the surge of sexual hormones that starts puberty. Gray matter grows throughout the brain but just before puberty its growth predominates in the frontal lobe of the brain, the part dedicated to reasoning, planning and impulse control. This gray matter won't be fully matured until a person is nearing the end of his teenage years, explaining why teenagers have difficulty with reasoning and impulse control. A 1999 study by A. Baird and colleagues in the "Journal of the American Academy of Child and Adolescent Psychiatry" showed the differences in the brain of pubescent teens. The brains of teens were monitored while they were asked to identify the emotions on people's faces in a series of pictures. The brains of younger teens showed more action in the amygdala, the part of the brain responsible for fearful and instinctual reactions, than in the frontal lobe. Older teens showed more action in the frontal lobe, indicating that the brain matures during puberty.
