McKenna's Pharmacology for Nursing, 2e

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C H A P T E R 3 9 Introduction to the reproductive system

THE HUMAN SEXUAL RESPONSE Many animals require particular endocrine stimuli, called an oestrous cycle, for sexual response to occur. Humans and ferrets are the only animals known to be sexually stimulated and responsive at will. Humans can be sexually stimulated by thoughts, sights, touch or a variety of combined stimuli. The human sexual response consists of four phases: • A period of stimulation with mild increases in sensitivity and beginning stimulation of the sympathetic nervous system • A plateau stage when stimulation levels off • A climax, which results from massive sympathetic stimulation of the body • A period of recovery or resolution, when the effects of the sympathetic stimulation are resolved (Figure 39.6) Previously, it was believed that male and female responses were very different. However, it is now thought that the physiology of the responses is quite similar. Sexual stimulation and activity are a normal response and, in healthy individuals, are probably necessary for complete health of the body’s systems. The sympathetic stimulation causes increased heart rate, increased blood pressure, sweating, pupil dilation, glycogenolysis (break- down of stored glycogen to glucose for energy) and other sympathetic responses. This stimulation could be dan- gerous in some cardiovascular conditions that could be exacerbated by the sympathetic effects. In the male, the increased blood flow to the penis causes erection, which is necessary for penetration of the female and deposition of the sperm. Any drug therapy or disease process that interferes with the sympathetic response or the innerva- tion of the sexual organs will change the person’s ability to experience the human sexual response. This is import­ ant to keep in mind when teaching and when evaluating the effects of a drug.

■■ BOX 39.3  Effects of testosterone

Growth of male and sexual accessory organs (penis, prostate gland, seminal vesicles, vas deferens) Growth of testes and scrotal sac Thickening of vocal cords, producing the deep, male voice Hair growth on the face, body, arms, legs and trunk Male-pattern baldness Increased protein anabolism and decreased protein catabolism (this causes larger and more powerful muscle development) Increased bone growth in length and width, which ends when the testosterone stimulates closure of the epiphyses Thickening of the cartilage and skin, leading to the male gait Vascular thickening Increased haematocrit

CNS

Hypothalamus

GnRH

Anterior pituitary

FSH

LH

Seminiferous tubules

Interstitial or Leydig cells

Sperm Inhibin, oestrogens

Testosterone

occurs. This is similar to female menopause. The hypo- thalamus and anterior pituitary put out larger amounts of GnRH, FSH and LH in an attempt to stimulate the gland. If no increase in testosterone or inhibin occurs, the levels of GnRH, FSH and LH eventually return to normal levels. ■■ The testes produce sperm in the seminiferous tubules in response to FSH stimulation, and testosterone in the interstitial cells in response to LH stimulation. ■■ Testosterone is responsible for the development of male sex characteristics. These characteristics can be maintained by the androgens from the adrenal gland once the body has undergone the changes of puberty. KEY POINTS FIGURE 39.5  Interaction of the hypothalamic, pituitary, and testicular hormones that underlies the male sexual hormone system. CNS, central nervous system; FSH, follicle-stimulating hormone; GnRH, gonadotropin-releasing hormone; LH, luteinising hormone.

Climax (orgasm)

Plateau

Resolution

Excitement

FIGURE 39.6  Human sexual response.