Page 76 - 86 human physiology part-2

The Male Reproductive System

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
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
researched. 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 10-16 cm.

Although erections and orgasm can occur in prepubertal boys, they become much more common
during puberty, accompanied by development of libido (sexual desire). 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, and can occur even before reproductive capacity itself. 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.

If the foreskin of a boy does not become retractable during childhood, it normally begins to retract
during puberty. This occurs as a result of the increased production of testosterone and other hormones
in the body.

Genital Erection

The penis contains two chambers called the corpora cavernosa, which run the length of the organ.
A spongy tissue, full of muscle, veins, arteries, etc. fills these chambers. The corpora cavernosa are
surrounded by a membrane, called the tunica albuginea.

Erection begins with sensory or mental stimulation, or both. Impulses from the brain and local
nerves cause the muscles of the corpora cavernosa to relax, allowing blood to flow in and fill the
spaces. The blood creates pressure in the corpora cavernosa, making the penis expand. The tunica
albuginea helps trap the blood in the corpora cavernosa, thereby sustaining erection. When muscles in
the penis contract to stop the inflow of blood and open outflow channels, erection is reversed.

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