Genitalia (Male External)
The development of the external genitalia of males begins between seven and nine weeks after conception, in response to the production of a hormone called dihydrotestosterone by the testes. Before this time, the external genitalia of the male and female are indistinguishable.
During development, a region called the genital tubercle elongates to form the penis. Urogenital folds move toward each other to form a groove that will become the urethra (which connects to the bladder and through which urine is expelled). The urethral connection to the outside world through the penis is established between 11 and 14 weeks after conception. By 11 weeks the scrotum has developed as well.
The penis is the most obvious feature of the male external genitalia. The other constituents are the pubic air and the scrotum. The penis consists of a body (also called the shaft) and glans (also called the head). The body houses three columns of tissue, which can become engorged with blood. This causes the penis to become erect rather than flaccid. The bulk of the penis tissue is made up of the corpus cavernosum. Another tissue, the corpus spongiosum, runs underneath the penis. It can also fill with blood and participates in the formation of an erection.
At the tip of the penis there is a vertical slit. This is the urethral meatus. It is the opening of the urethra, through which both urine and semen flow.
The glans area of the penis is infused with nerve cells and is one of the most sensitive spots on the male body. A loose fold of skin called the foreskin or prepuce naturally covers it. In circumcised males, the foreskin is surgically removed just below the glans, exposing the glans. Circumcision is usually done for religious or cultural reasons and, until relatively recently, because it was thought to confer a health advantage on the male. However, a number of clinical studies have shown that although circumcised men have a slightly lower rate of penile cancer and bladder infections, when compared to uncircumcised men, the difference is not statistically significant. Whether the trauma of circumcision is balanced by any health advantage is a debatable point.
At the base of the penis lies the scrotum, a loose and wrinkled pouch. There are two compartments comprising the scrotum. Each of these contains a testicle. The testicles are oval in shape, rubbery in texture and, on average, about 1.77 in (4.5 cm) long. Sperm is produced in the testicles. Form there the sperm flows through the epididymis--a comma-shaped region at the back of each testicle--into the vas deferens, and joins the urethra in an organ called the prostate. During ejaculation the sperm is expelled from the penis.
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