American Medical Association Family Medical Guide - American Medical Association [238]
The male sex organs
The penis and the testicles are the most visible parts of the male reproductive system. The testicles are suspended in a pouch of skin called the scrotum. The testicles produce sperm and the male sex hormone testosterone. During sexual arousal, spongy tissue inside the penis becomes engorged with blood. Sperm travel from the testicles through a duct called the vas deferens into a pair of sacs called the seminal vesicles. The prostate gland and seminal vesicles produce a fluid that combines with the sperm to create semen—the fluid that is ejaculated at orgasm.
The Sexual Response Cycle
Men and women experience a predictable sequence of physical events as they become sexually aroused and begin to engage in sexual intercourse or masturbation. This sequence of events is called the sexual response cycle. The human sexual response cycle occurs in four stages—excitement, plateau, orgasm, and resolution. Men and women go through the same four stages, but the timing of the stages differs. For example, women usually take longer to become aroused during the excitement stage, although this is not always true. From beginning to end, a woman’s arousal and response cycle lasts almost four times longer than that of a man. This difference in timing is completely normal, but it can lead to sexual problems and misunderstanding if the partners are unaware of it. At the end of the sexual response cycle, men go through an additional phase, called the refractory period, during which they can no longer respond to sexual stimuli.
Excitement
Becoming sexually aroused depends on our ability to allow ourselves to focus on and experience effective sexual stimulation, which can be in the form of sexually stimulating touch, thoughts, or imagination. During the excitement, or arousal, stage, a woman’s vaginal lining secretes a lubricating fluid after erotic stimulation begins, making insertion of the penis easier and penetration more pleasurable. Her breasts, nipples, and labia swell, and her clitoris becomes engorged with blood. The man’s penis becomes erect, and his nipples also swell. Both men and women experience an accelerated heart rate and breathing as well as increased blood pressure. As arousal increases, blood flow to the sex organs increases. Late in this stage, many women and some men experience flushing on their chest. The excitement stage can last from a few minutes to several hours.
Plateau
The plateau stage is an advanced state of arousal preceding orgasm. This stage involves an acceleration of breathing, heart rate, and blood pressure experienced during the excitement stage. The outer third of the woman’s vagina swells and becomes longer, and the clitoris retracts to avoid direct stimulation by the penis. The man’s testicles enlarge and are drawn up into the scrotum, which tightens. A few drops of fluid that can contain sperm may appear at the tip of the penis. In both sexes, muscle spasms may occur in the face, hands, and feet. Muscle tension increases throughout the body. Men and women can move from the plateau phase to the resolution phase without having an orgasm.
Male and female sexual responses
Male and female sexual responses proceed through four stages—excitement, plateau, orgasm, and resolution. Women usually take longer to become aroused during the excitement phase and, generally, a woman’s sexual response cycle lasts about four times longer than that of a man. During the resolution stage, men go through a refractory period during which they do not respond to sexual stimuli and cannot have another orgasm for a certain length of time. Unlike