Penis

About the Penis

The penis is the external male organ through which both urine and semen leave the body through the urethra. It consists of a root attached to the pubic bones, a shaft, and the glans at the tip, which in uncircumcised males is covered by the foreskin, or prepuce. The shaft contains three cylinders of erectile tissue: the paired corpora cavernosa along the top and the corpus spongiosum underneath, which surrounds the urethra and expands to form the glans. During sexual arousal, nerve signals cause the release of nitric oxide, relaxing smooth muscle in the arteries and erectile tissue so that it fills with blood, while outflow through the veins is restricted, producing an erection. Erectile dysfunction is common with increasing age and is often linked to cardiovascular disease and diabetes. Other conditions include phimosis, a tight foreskin, Peyronie disease, in which fibrous scar tissue causes curvature, priapism, a prolonged erection that is a medical emergency, and congenital variations such as hypospadias.