(ē-rĕk'shŭn )

The state of swelling, hardness, and stiffness observed in the penis and to a lesser extent in the clitoris, generally due to sexual excitement. It is caused by engorgement with blood of the corpora cavernosa and the corpus spongiosum of the penis in men and the corpus cavernosa clitoridis in women.

Erection is necessary in men for the natural intromission of the penis into the vagina but not for the emission of semen. The blood withdraws from the penis after ejaculation and the erection is reduced. Erection of the penis may occur as the result of sexual excitement, during sleep, or due to physical stimulation of the penis. Abnormal persistent erection of the penis due not to sexual excitement but to certain disease states is called priapism.

SEE: nocturnal emission; penile prosthesis; priapism.