An orgasm is a physiological, and to no small degree a psychological, response to sexual stimulation, that can be experienced by both males and females. The orgasm is one of nature's ways of making certain that an animal will engage in sexual intercourse, thus propagating own genes.
In a human male orgasm, there are rapid, rhythmic contractions of the prostate, urethra and the muscles at the base of the penis, which force stored semen to be expelled through the penis's urethral opening. This is referred to as ejaculation. The process usually takes from 3 to 10 seconds. The process is usually, but not always, extremely pleasurable. Note that it is possible to ejaculate without reaching orgasm, and to have an orgasm without ejaculation. Following orgasm, a refractory period occurs during which a man cannot have another orgasm. This period can be anywhere from one minute to over half an hour, depending on the individual and his age.
In a human female orgasm, orgasm is preceded by moistening of the vaginal walls, and an enlargement of the clitoris due to increased blood flow trapped in the clitoris's spongy tissue. Some women exhibit a sex flush; a reddening of the skin over much of the body due to increased blood flow to the skin. As women come closer to having orgasm, the clitoris moves inward under the clitoral hood, and the labia minora (minor lips) become a darker pink. As orgasm becomes iminent, the vagina decreases in size by about 30% and also becomes congested with blood. The uterus then experiences muscular contractions. A women experiences full orgasm when her uterus, vagina and pelvic muscles undergo a series of rhythmic contractions.
After the orgasm is over, the clitoris re-emerges from under the clitoral hood, and returns to its normal size in less than 10 minutes. Unlike men, women do not have a refractory period, and thus can experience a second orgams soon after the first; some women can even follow this with a third, or even fourth orgasm; this is known as a multiple orgasm. Research shows that about 13% of women experience multiple orgasms; a larger number may be able to experience this with the proper stimulation and frame of mind.
Orgasms in both men and women are often associated with other involuntary actions, including vocalizations and muscular spasms in other areas of the body Also, a generally euphoric sensation is associated with orgasm.