According to Masters and Johnson (1966) there are four phases that the body of both male and females go through due to sexual stimulation. They are the Excitement Phase, the Plateau Phase, the Orgasmic Phase, and the Resolution Phase.
The Excitement Phase is the phase in which sexual stimulation first starts. The reaction is different in many ways for the male and female. In the male, there is the start of an erection, which takes 3 to 8 seconds to appear after sexual stimulation is first started. There is also a change in the skin around the penis. The scrotal skin thickens and the testes become larger and more drawn into the males body. In the female, there is the start of vaginal lubrication which can start as soon as 10 to 30 seconds after the start of sexual stimulation. Vasocongestion, which is the swelling of the genital tissue, will begin to swell the clitoris and flattens the vaginal lips. The inner vagina expands, the breasts enlarge, and blood vessels near surface become more prominent. In both the male and female, the nipples become more erect, the heart rate increases, as well as an increase in blood pressure.
The second phase of sexual arousal is the Plateau Phase. In this phase, the male will have an increase in the circumference of the head of the penis and it will take on a purplish hue. The testes become even more elevated into a position for ejaculation. They may also reach up to one and a half sizes larger than their normal size when not aroused. In the female, there is be contracting in the vaginal opening in preparation to grasp the penis. The inner vagina will continue to expand and the clitoris will withdraw beneath the clitoral hood and shorten. In both the male and female, there will be rapid breathing, increase in heart rate to 100-160 beats per minute, and blood pressure will continue to rise.
The third phase is the Orgasmic Phase in which everything begins to come to a peak. In the males, there are two different contractions of...