Page 163 - 86 human physiology part-2

Chapter 19

than in males, especially in the typical female distribution of breasts, hips, and thighs. This produces
the typical female body shape. Also, the fat goes to the buttocks of a girl, giving their buttocks more
shape and curve.

Body and facial hair in girls

In the months and years following the appearance of pubic hair, other areas of skin which respond
to androgens develop heavier hair (androgenic hair) in roughly the following sequence: underarm
(axillary) hair, perianal hair, upper lip hair, sideburn (preauricular) hair, and periareolar hair. Arm and
leg hair becomes heavier more gradually over 10 years or more. Although in Western culture, hair in
some of these areas is unwanted, it rarely indicates a hormone imbalance unless it occurs elsewhere as
well (such as under the chin and in the midline of the chest).

Height growth in girls

The estrogen-induced pubertal growth spurt in girls begins at the same time the earliest breast
changes begin, or even a few months before, making it one of the earliest manifestations of puberty in
girls. Growth of the legs and feet accelerates first, so that many girls have longer legs in proportion to
their torso in the first year of puberty. The rate of growth tends to reach a peak velocity (as much as
7.5-10 cm or 3-4 inches per year) midway between thelarche and menarche and is already declining by
the time menarche occurs. In the 2 years following menarche most girls grow about 5 cm (2 inches)
before growth ceases at maximal adult height. This last growth primarily involves the spine rather than
the limbs.

Body odor, skin changes, and acne

Rising levels of androgens can change the fatty acid composition of perspiration, resulting in a
more "adult" body odor. This often precedes thelarche and pubarche by 1 or more years. Another
androgen effect is increased secretion of oil (sebum) from the skin. This change increases the
susceptibility to acne vulgaris, a characteristic affliction of puberty greatly variable in its severity.

Male

The onset of puberty for males is simular to that of females. GnRH secretion from the
hypothalamus results in an increase in pituitary gonadatropins secretion LH / ICSH and FSH. The
pituitary gonadatropins stimulate the seminiferous tubules and testosterone secretion. Testosterone
causes changes in the accessory reproductive organs, secondary sex characteristics and male sex drive.

Testicular size, function, and fertility

In boys, testicular enlargement is the first physical manifestation of puberty (and is termed
gonadarche). Testes in prepubertal boys change little in size from about 1 year of age to the onset of
puberty, averaging about 2–3 cc in volume and about 1.5-2 cm in length. Testicular size continues to
increase throughout puberty, reaching maximal adult size about 6 years later. While 18-20 cc is
reportedly an average adult size, there is wide variation in the normal population.

The testes have two primary functions: to produce hormones and to produce sperm. The Leydig
cells produce testosterone (as described below), which in turn produces most of the changes of male

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