Page 164 - 86 human physiology part-2

Development: Birth Through Death

puberty. However, most of the increasing bulk of testicular tissue is spermatogenic tissue (primarily
Sertoli and interstitial cells). The development of sperm production and fertility in males is not as well
documented. Sperm can be detected in the morning urine of most boys after the first year of pubertal
changes (and occasionally earlier).

Genitalia

A boy's penis grows little from the fourth year of life until puberty. Average prepubertal penile
length is 4 cm. The prepubertal genitalia are described as stage 1. Within months after growth of the
testes begins, rising levels of testosterone promote growth of the penis and scrotum. This earliest
discernible beginning of pubertal growth of the genitalia is referred to as stage 2. The penis continues
to grow until about 18 years of age, reaching an average adult size of about 7-14 cm.

Although erections and orgasm occur in prepubertal boys, they become much more common
during puberty, accompanied by a markedly increased libido. Ejaculation becomes possible early in
puberty; prior to this boys may experience dry orgasms. Emission of seminal fluid may occur due to
masturbation or spontaneously during sleep (commonly termed a wet dream, and more clinically called
a nocturnal emission). The ability to ejaculate is a fairly early event in puberty compared to the other
characteristics. However, in parallel to the irregularity of the first few periods of a girl, for the first one
or two years after a boy's first ejaculation, his seminal fluid may contain few active sperm.

Pubic hair in boys

Pubic hair often appears on a boy shortly after the genitalia begin to grow. As in girls, the first
appearance of pubic hair is termed pubarche and the pubic hairs are usually first visible at the dorsal
(abdominal) base of the penis. The first few hairs are described as stage 2. Stage 3 is usually reached
within another 6–12 months, when the hairs are too numerous to count. By stage 4, the pubic hairs
densely fill the "pubic triangle." Stage 5 refers to spread of pubic hair to the thighs and upward towards
the umbilicus as part of the developing abdominal hair.

Body and facial hair in boys

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, periareolar hair, and the rest of
the beard area. Arm, leg, chest, abdominal, and back hair become heavier more gradually. There is a
large range in amount of body hair among adult men, and significant differences in timing and quantity
of hair growth among different ethnic groups.

Voice change

Under the influence of androgens, the voice box, or larynx, grows in both genders. This growth is
far more prominent in boys, causing the male voice to drop, rather abruptly, about one octave, because
the larger vocal folds have a lower fundamental frequency. Occasionally, this is accompanied by
cracking and breaking sounds in the early stages. Most of the voice change happens during stage 4 of
male puberty around the time of peak growth. However, it usually precedes the development of
significant facial hair by several months to years.

Height growth in boys

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