Porth's Essentials of Pathophysiology, 4e

1020

Genitourinary and Reproductive Function

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the external os , and the uterine opening, the internal os . The space between these two openings, which is called the endocervical (cervical) canal, provides a route for menstrual discharge and entry of sperm. Secretions from the columnar epithelium of the endocervix protect the uterus from infection, alter receptivity to sperm, and form a mucoid “plug” during pregnancy. Fallopian (Uterine) Tubes The fallopian , or uterine , tubes are slender cylindri- cal structures attached bilaterally to the uterus and supported by the upper folds of the broad ligament. 1,2 They are formed by smooth muscle and lined with a ciliated, mucus-producing epithelial layer. The end of the fallopian tube nearest the ovary forms a funnel- like opening with fringed, fingerlike projections, called fimbriae , that pick up the oocyte (egg cell) after its release into the peritoneal cavity following ovulation (see Fig. 40-4). The beating of the cilia, along with con- tractile movements of the smooth muscle, propel the nonmobile oocyte toward the uterus. Besides providing a passageway for ova and sperm, the fallopian tubes permit drainage of tubal secretions into the uterus. Ovaries The ovaries are almond-shaped organs located on either side of the uterus below the ends of the two fallopian tubes. 2 The ovaries are attached to the posterior surface of the broad ligament and to the uterus by the ovarian ligament (see Fig. 40-4). Structurally, the mature ovary is divided into a highly vascular inner medulla and an outer cortex. The medulla or medullary region is located in the central part of the ovary. It contains loose connective tissue, blood vessels, lymphatic vessels, and nerves. The ovarian cortex is composed of a connective tissue frame- work, the stroma (also known as the interstitial compart- ment), as well as ovarian follicles in various stages of development. The surface of the ovary is covered with a thin layer of surface epithelium that is continuous with the lining of the peritoneum. The integrity of this covering is periodically broken at the time of ovulation to allow for the release of the ovum, but then quickly repairs itself. The Menstrual Cycle Between menarche (i.e., first menstrual bleeding) and menopause (i.e., cessation of menstrual bleeding), the female reproductive system undergoes cyclic changes called the menstrual cycle . This includes the maturation and release of oocytes from the ovary during ovulation and periodic vaginal bleeding resulting from the shedding of the endometrial lining. It is not necessary for a woman to ovulate to menstruate; anovulatory cycles do occur. The menstrual cycle produces changes in the breasts, uterus, skin, ovaries, and perhaps other unidentified tissues. The menstrual cycle is regulated by a complex interac- tion between the hypothalamic-pituitary axis, the ovaries, and the uterus 3,4 (Fig. 40-5). Although each part of the reproductive system is essential to normal function, the

50

40

LH

30

20

FSH

10 Plasma concentration of gonadotropins (IU/L)

Day

5

10

15

20

25 28

15

Estrogen

10

5

Progesterone

Plasma concentration of steroids (IU/L)

Day

5

10

15

20

25 28

Ovarian cycle

Primary follicle

Ovulation at day 14

Corpus luteum

36.7 Endometrial cycle Temperature (°C) 36.4 36.1

Proliferative phase

Secretory phase

Day

5

10

15

20

25 28

Menstrual flow

Secretory phase

Proliferative phase

ovaries are primarily responsible for controlling the cyclic changes and the length of the menstrual cycle. In most women in the middle reproductive years, menstrual bleed- ing occurs every 25 to 35 days, with a median of 28 days. The Hypothalamic-Pituitary Axis The ovaries perform two interrelated functions—ste- roidogenesis, or production of the female sex hormones, and gametogenesis, or production of ova. Both of these functions are regulated by follicle-stimulating hormone FIGURE 40-5. Hormonal and morphologic changes during the normal menstrual cycle. FSH, follicle-stimulating hormone; LH, luteinizing hormone.