McKenna's Pharmacology for Nursing, 2e

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P A R T 7  Drugs acting on the reproductive system

The external genitalia—the clitoris, labia and vagina— are sites of erogenous stimulation and the entry way for sperm to reach the uterus to allow conception and the exit path for the developed fetus at birth. Development of the breast tissue, also considered a secondary sex char- acteristic, is controlled by the female sex hormones and is necessary for producing milk for the nourishment of the baby when it has been expelled from the uterus and is no longer able to be dependent on the mother’s blood supply for nourishment. Hormones The hormones produced in the ovaries are oestrogen and progesterone. These two hormones influence many other body systems while preparing the body for preg- nancy or maintenance of pregnancy. Oestrogen The oestrogens produced by the ovaries include oestrad­ iol, oestrone and oestriol. The oestrogens enter cells and bind to receptors within the cytoplasm to promote messenger RNA (mRNA) activity, which results in pro- duction of specific proteins for cell activity or structure. Many of these effects are first noticed at menarche (the onset of the menstrual cycle), when the hormones begin cycling for the first time. Female characteristics are associated with the effects of oestrogen on many of the body’s systems—wider hips, soft skin, breast growth and so on. Box 39.1 summarises the effects of oestrogen on the body. Progesterone Progesterone is released into circulation after ovulation. Progesterone has many effects that support the early development of the fetus. Progesterone’s effects on body temperature are monitored in the “rhythm method” of birth control to indicate that ovulation has just occurred. Box 39.2 summarises the effects of progesterone on the body. Control mechanisms The developing hypothalamus is sensitive to the andro- gens released by the adrenal glands and does not release GnRH during childhood. As the hypothalamus matures, it loses its sensitivity to the androgens and starts to release GnRH. This occurs at puberty , or sexual development. The onset of puberty leads to a number of hormonal changes. See Figure 39.2. GnRH stimulates the anterior pituitary to release FSH and LH. FSH and LH stimulate the follicles on the outer surface of the ovaries to grow and develop. These follicles, called Graafian follicles, produce progesterone, which is retained in the follicle, and oestrogen, which is released into circulation. When the circulating oestrogen level rises high enough, it stimulates a massive release of

■■ BOX 39.1  Effects of oestrogen

LH from the anterior pituitary. This is called the “LH surge”. This burst of LH causes one of the developing follicles to burst and release the ovum with its stored hormones into the system. LH also causes the rest of the developing follicles to shrink in on themselves, or involute and eventually disappear. The release of an ovum from the follicle is called ovulation . The ovum is released into the abdomen near the end of one of the fallopian tubes, and the constant movement of cilia within the tube helps to propel the ovum into Growth of genitalia (in preparation for childbirth) Growth of breast tissue (in preparation for pregnancy and breastfeeding) Characteristic female pubic hair distribution (a triangle) Stimulation of protein building (important for the developing fetus) Increased total blood cholesterol (for energy for the mother as well as the developing fetus) with an increase in high-density lipoprotein levels (“good” cholesterol, which serves to protect the female blood vessels against atherosclerosis) Retention of sodium and water (to provide cooling for the heat generated by the developing fetus and to increase diffusion of sodium and water to the fetus through the placenta) Inhibition of calcium resorption from the bones (helps to deposit calcium in the fetal bone structure; when this property is lost at menopause, osteoporosis, or loss of calcium from the bone, is common) Alteration of pelvic bone structure to a wider and flaring pelvis (to promote easier delivery) Closure of the epiphyses (to conserve energy for the fetus by halting growth of the mother) Increased thyroid hormone globulin (metabolism needs to be increased greatly during pregnancy, and the increase in thyroid hormone facilitates this) Increased elastic tissue of the skin (to allow for the tremendous stretch of the abdominal skin during pregnancy) Increased vascularity of the skin (to allow for radiation loss of heat generated by the developing fetus) Increased uterine motility (oestrogen is high when the ovum first leaves the ovary, and increased uterine motility helps to move the ovum towards the uterus and to propel the sperm towards the ovum) Thin, clear cervical mucus (allows easy penetration of the sperm into the uterus as ovulation occurs; used in fertility programs as an indication that ovulation will soon occur) Proliferative endometrium (to prepare the lining of the uterus for implantation with the fertilised egg) Anti-insulin effect with increased glucose levels (to allow increased diffusion of glucose to the developing fetus) T-cell inhibition (to protect the non-self cells of the embryo from the immune surveillance of the mother)