Porth's Essentials of Pathophysiology, 4e

1021

Disorders of the Female Genitourinary System

C h a p t e r 4 0

(FSH) and luteinizing hormone (LH) from the anterior pituitary gland 3,4 (Fig. 40-6). Because these hormones promote the growth of cells in the ovaries and testes as a means of stimulating the production of sex hor- mones, they are called the gonadotropic hormones . The secretion of LH and FSH is stimulated by gonadotro- pin-releasing hormone (GnRH) from the hypothalamus. These gonadotropins then trigger the ovary to release an oocyte that is capable of being fertilized. Concurrently, the ovary secretes hormones that act on the endome- trial lining of the uterus to prepare for implantation. In addition, the ovarian hormones provide feedback to the hypothalamus and pituitary regarding the secretion of gonadotropins during the menstrual cycle. In addition to LH and FSH, the anterior pituitary secretes a third reproductive hormone called prolactin . The primary function of prolactin is the stimulation of lactation in the postpartum period. During pregnancy, prolactin, along with other hormones such as estrogen, progesterone, insulin, and cortisol, contributes to breast development in preparation for lactation. Although prolactin does not appear to play a physiologic role in ovarian function, hyperprolactinemia can lead to hypo- gonadism. This may include an initial shortening of the luteal phase with subsequent absence of menstruation,

scanty menstruation, infrequent menstruation (periods more that 35 days apart), and infertility. The hypotha- lamic control of prolactin secretion is primarily inhibi- tory, and dopamine is the most important inhibitory factor. Hyperprolactinemia may occur as an adverse effect of drug treatment using phenothiazine derivatives (i.e., antipsychotic drugs that block dopamine receptors). Ovarian Hormones The ovaries produce estrogens, progesterone, and andro- gens (e.g., testosterone). In the ovary, the main source of hormone production are the maturing follicles, includ- ing the theca cells and granulosa cells (Fig. 40-7A), and the corpus luteum, the cell mass remaining in the ovary after the oocyte has been released (Fig. 40-7B). The theca cells produce androgens, the granulosa cells produce estrogen, and the corpus luteum produces pro- gesterone. The other stromal cells that contribute to the production of androgens can be divided into two popu- lations: the secondary interstitial cells (derived from the theca) and the cells of the hilum, the bridge of tissue through which blood vessels and nerves enter and exit the ovary (see Fig. 40-7B). These cells are the major ones involved in androgen production during menopause. 3,4 Estrogens. Estrogens are a family of structurally related female sex hormones synthesized and secreted by cells in the ovaries and, in small amounts, by cells in the adre- nal cortex. 3–5 Androgens can be converted to estrogens peripherally, especially in adipose tissue. Three estro- gens occur naturally in humans: estrone, estradiol, and estriol. Of these, estradiol is the most biologically potent and the most abundantly secreted product of the ovary. Estrogens are transported in the blood bound to spe- cific plasma globulins, inactivated and conjugated in the liver, and then excreted in the bile. Estrogens are necessary for normal female develop- ment. 3–5 They stimulate the development of the vagina, uterus, and uterine tubes in the embryo. They also stim- ulate the stromal development and ductal growth of the breasts at puberty, are responsible for the accelerated pubertal skeletal growth phase and for closure of the epiphyses of the long bones, contribute to the growth of axillary and pubic hair, and alter the distribution of body fat to produce the typical female body contours. In concert with other hormones, estrogens provide for the reproductive processes of ovulation, implantation of the products of conception, pregnancy, parturition, and lactation by stimulating the development and maintain- ing the growth of the reproductive organs. Estrogens also have a number of other important met- abolic effects. They are responsible for maintaining the normal structure of skin and blood vessels in women. Estrogens decrease the rate of bone resorption by antago- nizing the effects of calcitonin on bone; for this reason, osteoporosis is a common problem in estrogen-deficient postmenopausal women (see Chapter 44). In the liver, estrogens increase the synthesis of transport proteins for thyroxine, estrogen, testosterone, and other hormones. Estrogens also affect the composition of the plasma

Cerebral cortex, limbic system and other brain centers

Hypothalamus

GnRH

Anterior pituitary

Feedback

LH

FSH

Ovary

Theca interna

Corpus luteum

Estrogen

Progestin

Target tissues

Target tissues

FIGURE 40-6. Hypothalamic-pituitary feedback control of estrogen and progesterone levels in the female.The dashed line represents negative feedback. FSH, follicle-stimulating hormone; GnRH, gonadotropin-releasing hormone; LH, luteinizing hormone.