Reproductive Anatomy (p. 1050)
1. In the female fetus, the absence of testosterone and müllerian inhibiting factor results in the paramesonephric duct developing into the uterine tubes, uterus, and vagina and the external genitalia developing into a clitoris, labia minora, and labia majora.
2. The ovary has a central medulla, a surface layer of parenchyma called the cortex, and an outer fibrous capsule, the tunica albugínea. The ovary is supported by three ligaments and supplied by an ovarian artery, ovarian veins, and ovarian nerves.
3. Each egg develops in its own bubblelike follicle. Follicles are located primarily in the cortex.
4. The uterine (fallopian) tube is a ciliated duct that extends from the ovary to the uterus.
5. The uterus is a thick muscular chamber superior to the urinary bladder. It consists of an upper fundus, middle corpus (body), and lower cervix (neck), where it meets the vagina.
6. The uterine wall consists of an outer serosa called the perimetrium, a thick muscular myometrium, and an inner mucosa called the endometrium. The endometrium contains numerous tubular glands and is divided into two layers—a thick superficial stratum functionalis, which is shed in each menstrual period, and a thinner basal stratum basalis, which is retained from cycle to cycle.
7. The uterus is anchored by four pairs of ligaments and supplied with blood by a uterine artery that arises from each internal iliac artery.
8. The vagina tilts dorsally between the urethra and rectum. It has no glands but is moistened by transudation of serous fluid through the vaginal wall and by mucus from glands in the cervical canal.
9. The vulva (pudendum or external genitalia) include the mons pubis, labia majora and minora, clitoris, vaginal orifice, accessory glands (greater and lesser vestibular glands and paraurethral glands) and erectile tissues (vestibular bulbs). The urethra also opens into the vulva.
10. The breast is internally divided into lobes, each with a lactiferous duct that conveys milk to the nipple. Outside of pregnancy or lactation, the breast contains only small traces of mammary gland.
11. Breast cancer strikes a high percentage of women. Two breast cancer genes are known, although most cases are nonhereditary and have no association with identifiable risk factors.
Puberty and Menopause (p. 1058)
1. In the United States and Europe, female puberty typically begins around age 9 or 10. Rising GnRH levels trigger the secretion of FSH and LH. In response to FSH, the ovaries secrete estrogens, progesterone, inhibin, and androgens.
2. The earliest visible sign of puberty is breast development, or thelarche, which is stimulated by estrogen, progesterone, prolactin, glucocorticoids, and growth hormone.
3. Pubarche is the development of pubic and axillary hair, sebaceous glands, and axillary sweat glands. Androgens induce pubarche and activate the female libido.
4. Menarche is a girl's first menstrual period, occurring at an average age of 12 in the United States and Europe. The first few menstrual cycles are usually anovulatory; ovulation becomes regular about a year after menarche.
5. The estradiol of puberty induces development of the ovaries and secondary sex organs, has feminizing effects on the external anatomy, and stimulates bone growth. Progesterone acts primarily on the uterus, and inhibin modulates FSH secretion.
6. With age, the number of ovarian follicles declines and with it, the source of estrogen and progesterone. The decline in levels of steroids brings on a transitional period of climacteric, lasting a few years and marked by menopause, the eventual cessation of ovulation and menstruation.
Oogenesis and the Sexual Cycle (p. 1061)
1. The sexual cycle is the monthly cycle of events that occurs when a woman is not pregnant. It includes the ovarian cycle of events in the ovaries and the menstrual cycle of events in the uterus.
2. Oogenesis is the production of eggs. Unlike spermatogenesis, it occurs in a monthly rhythm and usually produces only one gamete (egg) per month.
3. Oogenesis begins with oogonia, which multiply until the fifth month of a girl's fetal development. Some of these develop into primary oocytes and begin meiosis I before birth. Most primary oocytes undergo atresia during childhood, leaving about 400,000 at puberty.
4. Surviving primary oocytes undergo meiosis I to produce a small first polar body, which dies, and a secondary oocyte. The secondary oocyte progresses only as far as metaphase II if it is not fertilized. If fertilized, it completes meiosis II, producing a second polar body, which also dies, and an ovum that goes on to become the zygote.
5. The ovarian cycle, occurring in the absence of pregnancy, typically lasts about 28 days, with day 1 considered to be the first day of visible menstruation.
6. The follicular phase of the cycle is divided into the menstrual phase (days 1-5 of the typical cycle) and preovulatory phase (days 6-14). It includes shedding of the endometrial stratum functionalis (menstruation), mitotic regrowth of endometrium, and follicular development. Under the influence of FSH, the follicles
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1084 Part Five Reproduction and Development progress from primordial follicles to primary follicles to secondary (antral) follicles, and finally, usually a single mature (graafian) follicle.
7. Ovulation is the release of an egg by the bursting of the mature follicle. It occurs on day 14 of the typical cycle and takes 2-3 minutes. It is triggered primarily by a surge in LH secretion.
8. The postovulatory phase is divided into the luteal phase (days 15-26) and premenstrual phase (days 27-28). The luteal phase is marked by transformation of the mature follicle into a corpus luteum, which secretes progesterone; by thickening of the endometrium; and eventually by atrophy, or involution, of the corpus luteum. The premenstrual phase is marked by ischemia and necrosis of the stratum functionalis.
9. The menstrual cycle is divided into proliferative, secretory, premenstrual, and menstrual phases.
10. The proliferative phase (days 6-14) is a period of rebuilding the lost stratum functionalis by mitosis under the influence of estrogen from the ovaries.
11. The secretory phase (days 15-26) is a period of thickening of the endometrium by secretion of mucus and glycogen under the influence of progesterone from the corpus luteum.
12. The premenstrual phase is a period triggered by involution of the corpus luteum and the resulting lack of progesterone. Spasms of the spiral arteries deprive the endometrium of blood flow, resulting in necrosis and sloughing off of the stratum functionalis. The menstrual phase begins when enough necrotic tissue and blood have accumulated to produce noticeable vaginal discharge of menstrual fluid.
Female Sexual Response (p. 1068)
1. Female sexual response occurs in stages similar to that of the male, with the following major differences: In the excitement phase, the labia majora and minora, the clitoris, and the breasts become vasocongested; secretions of the greater vestibular glands lubricate the vulva; and the vagina is moistened by vaginal transudate. The inner end of the vagina dilates and its lower end constricts to form a narrow passage, the orgasmic platform. The uterus rises from its forward-tilted position to a nearly vertical one (the tenting effect).
2. In orgasm, the paraurethral glands secrete into the vulva, the orgasmic platform of the vagina constricts repeatedly, and the cervix plunges into the vaginal canal (into the semen if present).
3. In resolution, the uterus returns to its forward tilt, the orgasmic platform relaxes, the breasts become less congested, and there may be an outbreak of perspiration. Unlike men, women lack a refractory period and may experience successive orgasms.
Pregnancy and Childbirth (p. 1070)
1. Gestation lasts an average of 266 days from conception to birth, but birth is predicted to occur about 280 days from the onset of the last menstrual period.
2. Fertilization occurs in the distal half of the uterine tube and the fertilized egg divides five or six times before reaching the uterus. All the products of fertilization—the embryo or fetus and the associated membranes—are called the conceptus.
3. The major hormones of pregnancy are human chorionic gonadotropin (HCG), estrogens, progesterone, and human chorionic somatomammotropin (HCS).
4. HCG stimulates the corpus luteum to grow and secrete estrogen and progesterone. Estrogen from the corpus luteum and later from the placenta stimulates tissue growth in the mother and fetus and softens joints of the mother's pelvic girdle in preparation for giving birth. Progesterone from the corpus luteum and placenta inhibits premature uterine contractions and stimulates the mitosis of uterine decidual cells that nourish the early conceptus. Estrogen and progesterone also promote mammary gland development and inhibit the secretion of FSH. HCS from the placenta mobilizes fatty acids as fuel for the mother while it spares glucose for use by the fetus.
5. Thyroid hormone, parathyroid hormone, glucocorticoids, aldosterone, and relaxin also contribute to the developments of pregnancy (table 28.2).
6. Morning sickness, constipation, and heartburn sometimes accompany pregnancy as steroid hormones inhibit intestinal motility and the growing uterus compresses the digestive organs. The basal metabolic rate rises and one may feel hot as a result. Nutrient intake must increase moderately to meet the needs of the fetus.
7. Blood volume and cardiac output increase in pregnancy. Pressure from the uterus may cause hemorrhoids or varicose veins.
8. Breathing becomes more rapid in pregnancy as O2 demand and CO2 sensitivity increase, yet pressure from the uterus indirectly compresses the lungs and makes breathing shallower.
9. Glomerular filtration and urine output increase to dispose of both fetal and maternal wastes, but the capacity of the bladder is reduced by pressure from the uterus.
10. The maternal skin grows, especially on the breasts and abdomen; dermal tearing may cause striae; and some women exhibit melanization of the skin on the abdomen (linea nigra) or face (chloasma).
11. In the seventh month, the fetus usually turns into the vertex (head-down) position.
12. Late in pregnancy, the uterus becomes more contractile, sometimes exhibiting Braxton-Hicks contractions weeks before the true labor contractions occur. A rising ratio of estrogen to progesterone may be responsible for this increased contractility late in pregnancy. True labor contractions are stimulated by uterine stretching and oxytocin (OT).
13. According to the positive feedback theory of labor, stretching of the cervix triggers reflex contraction of the uterine body, which pushes the fetus downward and stretches the cervix still more. Cervical stretching also activates a neuroendocrine reflex that results in OT secretion, and OT stimulates more and more intense uterine contractions. The voluntary abdominal muscles also aid in giving birth.
14. The dilation (first) stage of labor involves dilation of the cervical canal to a diameter of 10 cm and thinning (effacement) of the cervical tissue. The fetal membranes typically rupture and discharge the amniotic fluid during this stage.
15. The expulsion (second) stage begins when the baby's head enters the vagina and lasts until the baby is entirely discharged. An attendant
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Physiology: The Unity of Reproductive System Companies, 2003 Form and Function, Third Edition usually drains, clamps, and cuts the umbilical cord at the end of this stage.
16. The placental (third) stage is the discharge of the placenta, amnion, and other components of the afterbirth. The afterbirth is inspected to be sure it has all been discharged and that it shows no abnormalities.
17. The puerperium is a period of 6 weeks postpartum marked by involution of the uterus and the return of other maternal anatomy and physiology to the pregravid state.
Lactation (p. 1076)
1. During pregnancy, estrogen, growth hormone, insulin, glucocorticoids, and prolactin stimulate growth and branching of the ducts of the
mammary glands. Progesterone then stimulates the development of secretory acini at the ends of the ducts.
2. For 1 to 3 days postpartum, the mammary glands secrete a fluid called colostrum rather than milk. Colostrum is higher than milk in protein but lower in fat and lactose. It contains immunoglobulins that give the neonate some immunity to infection.
3. Prolactin is secreted during pregnancy but cannot stimulate milk synthesis until after the placenta is shed. The mammary glands begin releasing milk about 2 or 3 days postpartum.
4. The nursing infant stimulates neuroendocrine reflexes in which the pituitary gland secretes oxytocin and
prolactin. Oxytocin triggers contraction of myoepithelial cells of the acini, making milk flow down the lactiferous ducts to the nipple. Prolactin stimulates synthesis of the milk that will be used for the next feeding.
5. Breast milk changes composition over the first two weeks and varies at different times of day and over the course of a single feeding. Most lactose and protein are delivered to the infant at the beginning of a feeding, and most fat at the end.
6. A woman nursing one infant eventually produces about 1.5 L of milk per day at a cost of 50 g of fat, 100 g of lactose, and 2 or 3 g of calcium phosphate. Her diet must compensate for these demands.
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