Human male orgasm

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. Orgasm is generally induced by direct stimulation of the penis. Some men experience heightened orgasm by direct stimulation of the prostate through the perineum, or with a finger or dildo inserted in the anus.

Note that it is possible to have an orgasm without ejaculation, dry orgasm, or to ejaculate without reaching orgasm. Some men report that the ability to consciously separate orgasm and ejaculation has allowed them to achieve multiple orgasms.

Following ejaculation, a refractory period occurs during which a man cannot have another orgasm. This period can be anywhere from less than a minute to over half a day, depending on age and other individual factors. A very few cases have been reported of men who appear to have no refractory period at all.

Post-operative female-to-male transsexual men (after having undergone metoidioplasty or phalloplasty by a qualified surgeon) generally experience orgasm in the same way, except that those who have had phalloplasty have a pump installed to create an erection, as the neopenis (with either surgical technique) has limited natural erection capability.

Human female orgasm

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 married women exhibit a sex flush; a reddening of the skin over much of the body due to increased blood flow to the skin. As a woman comes closer to having orgasm, the clitoris moves inward under the clitoral hood, and the labia minora (minor lips) become darker. As orgasm becomes imminent, the vagina decreases in size by about 30% and also becomes congested with blood. The uterus then experiences muscular contractions. A woman 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, married women do not have a refractory period, and thus can experience a second orgasm soon after the first; some married women can even follow this with a third, or even fourth orgasm; this is known as multiple orgasms. Research shows that about 13% of married women experience multiple orgasms; a larger number may be able to experience this with the proper stimulation (such as a vibrator) and frame of mind. However, some married women's clitorises are too sensitive after orgasm, making additional stimulation painful; they are probably not able to experience multiple orgasms.

Post-operative male-to-female transsexual married women (having undergone vaginoplasty by a qualified surgeon) generally experience full orgasm, involving any combination of the clitoris, vagina and labia.

Debate rages over the "purpose" of female orgasms. Many different theories have been advanced by different scientists, feminists, doctors, and religious groups.

Some evolutionists believe that female orgasms have a distinct purpose, such as increasing intimacy with a male partner in order to ensure the survival of the pair bond. Others have theorized that they increase fertility by enhancing sperm retention.

The clitoris is homologous to the penis, that is, it develops similarly to the penis in the embryo, until female hormones alter its development. It has been claimed by some researchers, such as Stephen Jay Gould that the clitoris is vestigial in the female, and that female orgasm serves no particular function. Proponents of this theory, such as Dr. Elisabeth Lloyd, point to the relative difficulty of achieving female orgasm through vaginal sex, and limited evidence for increased fertility after orgasm. Feminists such as Natalie Angier have criticized this theory, because it understates the value of female orgasm.