The Penis

Anatomy

Urethral Opening: Located at the end of the penis, the urethral opening is the end of the urethra, the tube through which urine and ejaculate exit the body. The inside of the urethra has spiral grooves that cause urine to flow in a narrow stream.

Glans: Also called the "head", the glans is the acorn-shaped structure at the end of the penis. It is well-endowed with nerve endings and is very sensitive to touch.

Frenulum: The small strip of skin that runs between the glans and shaft on the underside of the penis. The frenulum is very sensitive to stimulation and can produce significant pleasure for some males.

Shaft: The shaft is the long, cylindrical part of the penis that connects the glans to the base. It is made up of three parts: two corpora cavernosa and the corpus spongiosum.

Corpora Cavernosa: Cylinders of porous erectile tissue that make up a large part of the penile shaft and connect the head of the penis to the base. The corpora cavernosa engorge with blood upon sexual arousal, which causes the first phase of penile erection.

Corpus Spongiosum: Also known as the “spongy body,” this tissue forms the glans of the penis, runs along the bottom side of the shaft, and encircles the urethra. As the erection continues to develop, the corpus spongiosum fills with blood. It can be seen as a raised, vein-like column along the bottom of the penis. The corpus spongiosum also functions to keep the urethra from closing: it remains flexible while the corpora cavernosa remain stiff

Base: The base or bulb of the penis is a rounded mass of tissue at the end of the corpus spongiosum (the bottom of the penis). The base of the penis is located above the scrotum. Similarly to the penis bulb, the vestibule bulb is present in women.

Scrotum: A loose sac of skin that hangs below the penis and encompasses both of the testes. The distance that the scrotal sac hangs below the body changes with temperature: in cold temperatures, it moves closer to the body, and in hot temperatures, it hangs farther away from the body. This movement helps keep the testes a few degrees cooler than normal body temperature, a condition needed for most effective sperm production. In cold conditions, the testes are held closer to the body so that they are kept at a warmer temperature than their surrounding environment.

Penile Skin: The penile skin is continuous with the skin of the lower abdomen. The glans is covered with smooth, hairless skin.  Below the glans, at the corona, the skin folds onto itself to form the foreskin, which lies on top of the glans when flaccid (circumcised men lack foreskin). The penile skin is attached loosely to the smooth muscle tissue beneath it.

Foreskin: The loose skin that covers the head of an uncircumcised penis (while it is flaccid). The foreskin typically pulls back when a male becomes aroused and the penis becomes erect. If a male is circumcised, the foreskin will have been previously removed.1