Page 165 - 86 human physiology part-2

Chapter 19

Compared to girls' early growth spurt, growth accelerates more slowly in boys and lasts longer,
resulting in a taller adult stature among males than females (on average about 10 cm or 4 inches). The
difference is attributed to the much greater potency of estradiol compared to testosterone in promoting
bone growth, maturation, and epiphyseal closure. In boys, growth begins to accelerate about 9 months
after the first signs of testicular enlargement and the peak year of the growth spurt occurs about 2 years
after the onset of puberty, reaching a peak velocity of about 8.5–12 cm or 3.5–5 inches per year. The
feet and hands experience their growth spurt first, followed by the limbs, and finally ending in the
trunk. Epiphyseal closure and adult height are reached more slowly, at an average age of about 17.5
years. As in girls, this last growth primarily involves the spine rather than the limbs.

Male musculature and body shape

By the end of puberty, adult men have heavier bones and nearly twice as much skeletal muscle.
Some of the bone growth (e.g., shoulder width and jaw) is disproportionately greater, resulting in
noticeably different male and female skeletal shapes. The average adult male has about 150% of the
lean body mass of an average female, and about 50% of the body fat.

This muscle develops mainly during the later stages of puberty, and muscle growth can continue
even after a male is biologically adult. The peak of the so-called "strength spurt," the rate of muscle
growth, is attained about one year after a male experiences his peak growth rate.

Breast development in boys: pubertal gynecomastia

Estradiol is produced from testosterone in male puberty as well as female, and male breasts often
respond to the rising estradiol levels. This is termed gynecomastia. In most boys, the breast
development is minimal, similar to what would be termed a "breast bud" in a girl, but in many boys,
breast growth is substantial. It usually occurs after puberty is underway, may increase for a year or two,
and usually diminishes by the end of puberty. It is increased by extra adipose tissue if the boy is
overweight.

Although this is a normal part of male puberty, breast development for some boys is as unwelcome
as upper lip hair in girls. If the boy's distress becomes too substantial during development, the problem
can be removed or corrected surgically.

Adolescence

Adolescence is the period of psychological and social transition between childhood and adulthood.
Adolescence is the transitional stage of human development in which a juvenile matures into an adult.
This transition involves biological, social, and psychological changes, though the biological ones are
the easiest to measure objectively. The time is identified with dramatic changes in the body, along with
developments in a person's psychology and academic career. In the onset of adolescence, children
usually complete elementary school and enter secondary education, such as middle school or high
school. A person between early childhood and the teenage years is sometimes referred to as a pre-teen
or 'tween.

Physical maturation resulting from puberty leads to an interest in sexual activities, sometimes
leading to teenage pregnancy. Since teens may not be emotionally or mentally mature enough or
financially able to support children, sexual activity among adolescents is sometimes considered

380 | Human Physiology