The second stage, excitement or arousal, is due to spinal cord release of parasympathetic nerve impulses traveling along the pelvic nerves to the uterovaginal plexus. The end result is vascular engorgement of the clitoris, which results in lengthening and thickening of the clitoral organ, vasodilatation of the perivaginal blood supply causing transudation of fluid through the vaginal epithelium which appears to the partners as "wetness" or "lubrication."
Estrogen is required for this transudation and results in lubrication by maintaining the health of the vaginal mucosa. Continued vasocongestion of the vagina causes blood sequester in the upper half of the vagina leading to ballooning of the distal portion and elevation of the uterus. The excitement phase also causes vasodilatation in the breasts leading to increased breast size, nipple erection, and engorgement of the surrounding areola. Pulse, blood pressure, and respiratory rates increase and muscle tension throughout the body also increases. A sexual flush causing redness and erythema of the face, neck, chest, and frequently much of the body occurs in 75 percent of women. Pelvic and extragenital changes culminate in the "Plato phase" of the excitement stage where the clitoris retracts beneath its protective foreskin or hood. Vasocongestion occurs in the outer-third of the vagina with swelling to form the so called "orgasmic platform."
Orgasm is characterized by maximum physical and emotional excitement. This is accompanied by a series of involuntary ( 0.86 second) contractions of the rectal and urethral muscles as well as the uterus. Orgasm is a reflex and requires the woman to relinquish her sense of control and in addition for the orgasmic response to be activated stimulation primarily of the clitoris must be applied and must be of sufficient intensity and duration to reach the threshold for this reflex. Masters and Johnson showed that female orgasm almost always involves clitoral stimulation.
The last stage is resolution in which blood flow and pelvic congestion along with bodily tensions resolves within seconds unless the woman returns to orgasm. Females do not always fall back to the low excitement stage and many women are capable of returning to excitation with stimulation that can rapidly produce a repeat orgasm. Whether the orgasmic experience is multiple or single, resolution of all excitement phase changes may take one hour or longer in contrast to men.
Classification of Female Sexual Dysfunction
Classification of female sexual dysfunction was first developed by an international consensus conference in 1998 and formalized and published in 2000. FSD is divided into four categories: sexual desire disorder, sexual arousal disorder, orgasmic disorder, and sexual pain disorder. A significant addition was "causing personal distress." This has implication for women who are happy with their frequency and response to sexual activity; however, their partners may not be. This incompatibility among couples may require counseling; however, the women will no longer be labeled with the diagnosis of FSD.
Disorders of Sexual Desire
Hypoactive sexual desire disorder (HSDD) is the persistent or recurrent absence of sexual fantasy, thought, or desire for sexual activity which causes personal distress. Lowen reported an incidence of 22 percent, others as high as 55 percent, and appears to represent the most common form of FSD. All aspects of sexuality can cause HSDD. Psychosocial aspects of the relationship between partners appears to be a major cause. The couch potato, football watching, beer drinking husband is not uncommon. Demanding careers, raising children, motherhood, stressful life milestones, job loss, and the death of a loved one can all play a role. On the other hand, physical factors such as general health conditions, drug and alcohol abuse, aging, and many of the antidepressants may have a potential affect as well.