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PHYSICAL DEVELOPMENT
Two boys exactly
the same age can begin or complete puberty years apart, yet still fall with
the broad parameters of "normal" growth. The timing and pace of a teen's
physical development is determined largely by the genetic programming
inherited from parents.
Every year from age two or three to adolescence, a child grows an average of
two inches and gains about five pounds. During adolescence, that rate
typically doubles. Over the course of two to four adolescent years, teens
gain up to 25 percent of their adult height and up to 40 percent of their
adult weight. Major organs double in size. Here's how teens typically
develop:
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The hands and
feet grow first, resulting in a frequently awkward appearance.
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Next the
thighs widen and boys' shoulders and girls' hips broaden.
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Then the trunk
of the body lengthens.
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The bones in
the face also grow, particularly the lower jaw.
At the same time
that teens experience dramatic physical growth, they also experience
hormonal changes. Hormones are chemical messengers produced by the body's
glands that travel through the bloodstream to regulate specific cells and
organs. They are central to growth, sexual characteristics, procreation,
metabolism, personality traits and mood.
Sometime between the ages of seven and eleven in girls, and nine and a half
to thirteen and a half in boys, the pituitary gland at the base of the brain
releases two hormones that signal a girl's ovaries and boy's testicles to
begin producing the female sex hormone, estrogen, and the male sex hormone,
testosterone, respectively.
Each sex hormone than instructs reproductive structures (the ovaries,
uterus, fallopian tubes and vagina in girls; the testes, penis, vas deferens
and epididymis in boys) to develop or mature in preparation for one day
being able to bear or father children. Estrogen and testosterone also
trigger the development of secondary sex characteristics, which encompass
other male-female distinctions, such as women's breast and rounded hips, and
men's facial hair and muscle development. The growing ovaries and testicle
secrete increasing amounts of sex hormones, further fostering the process of
puberty.
Source: American Academy of Pediatrics |
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