Penis

The penis is the external reproductive organ of men and certain other vertebrate animals. In humans, it has two functions: conducting urine during urination and delivering semen during sexual intercourse. It consists of erectile tissue filled with blood vessels, which causes the penis to become rigid during erection.

The penis shares embryological origin with the clitoris in women; both develop from the same tissue in the fetus, but hormones—particularly androgens—direct their different development during gestation.

Structure

The penis is divided into three main parts: the root, attached to the pelvic bones; the shaft; and the glans (head). The shaft contains three columns of blood-filled tissue: two called the corpora cavernosa, located on the upper surface, and one called the corpus spongiosum, located below and containing the urethra. The glans is the enlarged end of the corpus spongiosum and the most sensitive part.

The glans is covered by a mucous membrane called the foreskin (or prepuce), which contains nerve endings and is sometimes surgically removed (circumcision). The urethra opens at the tip of the glans; both urine and semen are discharged through this opening, though not simultaneously, because during erection an internal mechanism blocks the flow of urine.

Function and erection

Erection results from changes in blood circulation: physical or psychological stimulation causes muscles in the blood vessels supplying the penis to contract, which fills the spongy tissue columns with blood. The pressure of blood in these tissues compresses the outflow vessels, trapping blood inside. Following stimulation, ejaculation may occur, involving secretions from the prostate gland, seminal vesicles, and sperm ducts. When stimulation ceases, the blood drains out and the penis returns to its flaccid state.

Size and variation

Penis size varies considerably among individuals and is influenced by genetics, hormones, and body structure. Flaccid size is generally not a reliable predictor of erect size. Various research studies have reported different measurements, as measurement methods and study populations differ.

Health and common conditions

Health conditions affecting the penis include erectile dysfunction, usually related to circulatory, metabolic, hormonal, or psychological factors; phimosis, in which the foreskin is too tight; hypospadias, in which the urethral opening is located away from its normal position on the glans; and Peyronie's disease, which causes penile tissue to develop abnormal curvature. Sexually transmitted infections can also produce symptoms affecting the penis. Penile cancer is rare compared with other cancer types.

Culture and society

The penis holds symbolic meaning in many cultures, associated with masculinity, reproduction, and power, as evidenced in ancient art, mythology, and linguistic expressions. Male circumcision is a widespread cultural and religious practice in Islam, Judaism, and many African and Asian societies, and is also performed for health reasons.