Physical Development of Adolescents—Tips for Parents
By Robert T. Brown, M.D.
The changes that occur in the bodies of adolescents as they mature
into adults are amazing. In just a few short years, these little children
become large adults capable of reproduction. They grow several inches
taller, their faces change in proportion, the genitals and secondary sex
characteristics develop, muscles develop, and fat shifts to different
locations. It's a real wonder.
In this brief description of the physical changes (puberty) that occur
during adolescence I will try to convey to parents how marvelous and
fascinating all these changes are, particularly when they and their
children are informed ahead of time about what the changes will be and
when they will happen.
During childhood, a small area in the base of the brain (the arcuate
nucleus), and a gland in the same location —the pituitary gland—
interact with the child's gonads (ovaries in girls, testicles in boys) in a
very finely tuned system that keeps the output of all three areas very
low. In other words, the amount of hormones secreted is kept very low.
This system is very much like a thermostat. Every time the
temperature goes up too much, the air conditioning comes on in order
to keep the temperature within a very narrow range.
Sometime in late childhood— and we don't know why these changes
start when they do— the brain area starts becoming less sensitive to
the hormones from the gonads (estrogen in girls and testosterone in
boys). This allows the brain to produce more of its hormone with the
result that the gonads are allowed to produce more of their hormones
before they are shut off. This increase in hormones continues
throughout puberty until the hormones reach adult levels in the blood.
As the amount of estrogen or testosterone on the blood increases, high
enough levels are reached for them to have impacts on the child's
body. That's when we see the beginning of puberty.
A second effect of these rising levels of estrogen or testosterone is the
stimulating effect that they have on the pituitary gland's production of
growth hormone. This causes the child's body to begin growing at a
faster rate that it had been doing, and the rapid increase quickly – in
just 3-5 years – brings the child to her or his full adult height. The
growth areas of the bones are also affected, and when they solidify,
growth is ended.
It is no secret to parents that the increasing gonadal hormones have a
large effect on what we call "secondary sex characteristics". This term
refers to breasts and body hair in girls and to the penis/testicles and
body hair in boys. Estrogen is the hormone in girls that makes the
breast enlarge, the lining of the vagina to change, and the uterus to
start having periods. A hormone from different glands, the adrenal
glands, is responsible for the growth of pubic hair and hair in the
armpits. In boys the active hormone for all the secondary sex changes
is testosterone, which also causes the testicles to make sperm.
Puberty starts as early as 6 or 7 years old and no later than 12 years
old in girls. It occurs as early as 8 or 9 years old and no later than 13
years old in boys. The whole process lasts about 4 years. Boys
generally start about two years later than girls, and the time during
puberty when there is very rapid increase in height – the growth spurt-
occurs earlier in a girl's pubertal development than in that of a boy. The
result is that in sixth, seventh, and eighth grades, girls usually are
much taller than boys. The boys catch up in the ninth and tenth
grades.
Girls' periods usually begin in mid-late puberty after they have had their
growth spurt. So when a girl has her first period – menarche – she only
has 1 or 2 inches of growth left. Early in a girl's menstrual life, her
ovaries usually don't put out an egg each month (ovulation). In most
girls, regular ovulation occurs 3 or 4 years after menarche.
Boys grow taller before their bodies devote much effort to building
muscles. Whey they have their growth spurt, their testicles are also
beginning to manufacture enough sperm that they might be able to
impregnate a girl if they had intercourse.
Girls do not lose body fat during puberty – they just shift it around. In a
child the fat tends to accumulate around the waist, but as she matures,
it shifts to the breasts, hips, and thighs. Boys, on the other hand, do
lose fat during their growth spurts. If they get fatter after they've finished
growing, it's because they didn't decrease their food intake after they
were finished growing.
As you can see, this whole process of puberty is really fascinating.
Armed with knowledge of what will happen and when, parents and
adolescents can face these changes with happy anticipation. If you
have further questions about puberty, contact your child's pediatrician.