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Physical Growth and Sexual Maturation of Adolescents
During adolescence (usually considered age 10 to the late teens or early 20s), boys and girls reach adult height and weight and undergo puberty (for boys, see Sexual Differentiation, Adrenarche, and Puberty; for girls, see Female Reproductive Endocrinology : Puberty). The timing and speed with which these changes occur vary and are affected by both heredity and environment.
A growth spurt in boys occurs sometime between ages 12 and 17, with the peak typically between ages 13 and 15; a gain of > 10 cm can be expected in the year of peak velocity. A growth spurt in girls occurs sometime between ages 9½ and 14½, with the peak typically between ages 11 and 13½; gain may reach 9 cm in the year of peak velocity. If puberty is delayed (see Delayed Puberty), growth in height may slow considerably. If the delay is not pathologic, the adolescent growth spurt occurs later and growth catches up, with height crossing percentile lines until the child reaches a genetically determined stature. At age 18, almost 2.5 cm of growth remains for boys and slightly less for girls, for whom growth is 99% complete. In girls with true precocious puberty (prior to age 6½), an early growth spurt occurs along with menarche at a young age and, ultimately, short stature results because of early closure of growth plates.
All organ systems and the body as a whole undergo major growth during adolescence; breasts in girls and genitals and body hair in both sexes undergo the most obvious changes. Even when this process goes normally, substantial emotional adjustments are required. If the timing is atypical, particularly in a boy whose physical development is delayed or in a girl whose development occurs early, additional emotional stress is likely. Most boys who grow slowly have a constitutional delay and catch up eventually. Evaluation to exclude pathologic causes and reassurance are needed.
Guidance concerning nutrition, fitness, and lifestyle should be given to all adolescents, with special attention paid to the role of activities such as sports, the arts, social activities, and community service in the adolescent’s life. Relative requirements for protein and energy (g or kcal/kg body weight) decline progressively from the end of infancy through adolescence (see Recommended Dietary Reference Intakes* for Some Macronutrients, Food and Nutrition Board, Institute of Medicine of the National Academies), although absolute requirements increase. Protein requirements are 0.9 g/kg/day in late adolescence; mean relative energy requirements are 40 kcal/kg.
Sexual maturation generally proceeds in an established sequence in both sexes. The age at onset and rapidity of sexual development vary and are influenced by genetic and environmental factors. Sexual maturity begins earlier today than a century ago, probably because of improvements in nutrition, general health, and living conditions—eg, the average age of menarche has decreased by about 3 yr over the past 100 yr. The physiologic changes that underlie sexual maturation are discussed in Male Reproductive Endocrinology and Related Disorders and in Female Reproductive Endocrinology.
In boys, sexual changes begin with enlargement of the scrotum and testes, followed by lengthening of the penis and enlargement of the seminal vesicles and prostate. Next, pubic hair appears. Axillary and facial hair appears about 2 yr after pubic hair. The growth spurt usually begins a year after the testes start enlarging. The median age for first ejaculation (between 12½ yr and 14 yr in the US) is affected by psychologic, cultural, and biologic factors. First ejaculation takes place about 1 yr after penis growth accelerates. Gynecomastia, usually in the form of breast buds, is common among young adolescent boys and usually resolves within several years.
In most girls, breast budding is the first visible sign of sexual maturation, followed closely by the initiation of the growth spurt. Shortly thereafter, pubic and axillary hair appears. Menarche generally occurs about 2 yr after onset of breast development and when growth in height slows after reaching its peak. Menarche occurs within a wide range, with most girls in the US starting their periods at 12 or 13 yr. The stages of breast growth and pubic hair development can be detailed using the Tanner method (see Figure: Puberty—when female sexual characteristics develop. and see Figure: Diagrammatic representation of Tanner stages I to V of human breast maturation.).
If the order of sexual changes is disturbed, growth may be abnormal, and the physician should consider pathologic reasons.
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