Chapter 26 The Reproductive System: Female
12. Define female climacteric.
After puberty, reproductive cycles continue at regular intervals until fourth or fifth decade when they become irregular • Female climacteric is period from onset of irregular menstrual cycles until their complete cessation; varies but can last as long as five years in some women.
7b. Further explain the roles of estrogen and progesterone.
Estrogen and progesterone stimulate development of following female sex characteristics: Maturation of sex organs and development of external genitalia Maintenance of anatomical features unique to adult females such as breast development and fat accumulation around hips and thighs • Progesterone is responsible for maintenance of a pregnancy once fertilization has occurred • Estrogens have effects on many other tissues including increasing bone density and increasing beneficial HDL cholesterol level • Estrogen promotes blood coagulation that can lead to formation of blood clots in specific circumstances.
11. Describe puberty in a female. Define menarche and explain the requirements for this process to occur.
PUBERTY - for most girls puberty begins between 9 and 11 years old, when secretion of estrogens and progesterone increases from ovaries Prior to puberty, low GnRH levels keep LH and FSH levels low; keeps estrogen and progesterone levels low as well At puberty, hypothalamus becomes less sensitive to low levels of estrogen and progesterone, and GnRH levels increase Elevated GnRH levels stimulate HPG axis, and blood levels of estrogen and progesterone increase; results in development of female secondary sex characteristics PUBERTY • First sign of puberty in girls is budding breasts followed by secondary sex characteristics: Appearance of pubic and axillary hair and an increase in secretions from sebaceous glands Adipose tissue increases in subcutaneous layer throughout body, with additional deposits in hips, thighs, and breasts Individual's height increases; hips widen MENARCHE - first episode of menstrual bleeding; occurs approximately two years after onset of puberty. Will not occur unless a girl has at least 15-17% body fat Leptin - hormone secreted by adipocytes; stimulates gonadotropin secretion If leptin levels drop due to low body fat percentage, gonadotropin levels decline; directly affects HPG axis.
5a. Define oogenesis and explain how it differs from spermatogenesis.
OOGENESIS - process in which female gametes, or ova, are produced • Differs from spermatogenesis in following ways: Begins before female infant is born, then is suspended until puberty Once reactivated at puberty continues until it ceases operation at menopause, somewhere between 45 and 55 years of age Occurs about once per month as a part of ovarian cycle. SEE TABLE SHOWING SPERMATOGENESIS AND OOGENESIS.
6. Describe the 3 phases of the ovarian cycle. Include what happens at each of the 7 stages and within what time frame each phase occurs.
OVARIAN CYCLE - includes monthly series of events associated with maturation of an oocyte and its follicle in an ovary. Maturation of one oocyte and its follicle takes many cycles, requiring up to 350 days to progress from primordial follicle to ovulation. Divided into three major phases: o Follicular Phase (Stages 1-4) o Ovulation Phase (Stage 5) o Luteal Phase (Stages 6-7) FOLLICULAR PHASE (stages 1-4): During this phase follicle grows and develops in following maturation events: STAGE 1: Primordial follicle - single layer of squamous follicular cells surrounds primary oocyte; during childhood, many primordial follicles begin their development into primary follicles. STAGE 2: Primary follicle - squamous follicular cells become cuboidal and are called granulosa cells; microvilli and thecal cells appear in primary follicle; forms a region called zona pellucida that becomes important once fertilization occurs STAGE 3: Secondary follicle: o Wall of follicle thickens and deeper granulosa cells secrete follicular fluid; forms small pockets and increases volume and size of follicle o Granulosa cells grow and stimulate cells in ovary to form a layer of thecal cells around follicle; in turn, granulosa cells produce estrogen from thecal cell secretions STAGE 4: Vesicular (tertiary) follicle: o Small pockets of follicular fluid merge into a single large cavity called antrum; primary oocyte and its capsule of granulosa cells project into antrum on a stalk o Follicle continues to enlarge, which creates a bulge on ovary surface; primary oocyte, suspended in prophase I, completes Meiosis I to form a secondary oocyte and first polar body o Newly formed secondary oocyte arrests development in metaphase II; will only complete second division if fertilization occurs OVULATION PHASE (stage 5) - event at end of follicular phase: Vesicular follicle erupts from ovary wall into peritoneal cavity ejecting its secondary oocyte and its granulosa cell layer, called corona radiata Vesicular follicle collapses and ruptured blood vessels bleed into antrum LUTEAL PHASE (stages 6-7): ruptured follicle becomes an endocrine organ called corpus luteum: Stage 6: Yellowish corpus luteum is formed by remaining granulosa cells and thecal cells o Secretes progesterone and some estrogen; will persist for about three months and then degrade if pregnancy does not occur Stage 7: Corpus albicans - whitish knot of scar tissue that marks end of one ovarian cycle; remnants of previously active corpus luteum after it ceases secreting hormones and is degraded by macrophages. Ovarian cycle averages about 28 days overall, with each stage accounting for following amount of time: Follicular phase extends from day one to day 14; may vary Ovulation on day 14; may vary Luteal phase extends from day 14 to day 28; relatively constant.
2. Trace the pathway of the female gamete from the ovary to the uterus. Identify the typical site of fertilization.
Ovulation - an immature gamete called an oocyte is expelled from ovary Fimbriae sweep ovary surface to catch oocyte and direct it into uterine tube Uterine tube uses smooth muscle peristaltic contraction and ciliated cells to move the oocyte from fimbriae to the ampulla, to the infundibulum and finally to the isthmus before it falls into the uterus o Nonciliated cells produce mucus-like secretion to keep oocyte moist and nourished Fertilization begins when a sperm cell binds to and penetrates oocyte plasma membrane; typically occurs in ampulla.
10. Describe the hormonal control of the uterine cycle.
Regulation of uterine function requires rhythmic fluctuation of hormones from HPG axis components. When menstrual phase of uterine cycle begins FSH and LH start rising while ovarian hormones are still low; by day 5, ovarian follicles increase estrogen production. During proliferative phase of cycle, estrogen levels rise and stimulate LH and FSH surges; trigger ovulation; ovulation produces a corpus luteum which releases progesterone. During secretory phase of cycle, rising progesterone levels and decreasing estrogen levels inhibit LH. If fertilization doesn't occur, progesterone levels decrease, stratum functionalis breaks down, and menstruation phase begins. If fertilization does occur, outer layer of developing embryo begins to secrete human chorionic gonadotropin (hCG); keeps corpus luteum from degenerating and progesterone levels remain elevated.
7a. Describe the hormonal control of the ovarian cycle.
Regulation requires a rhythmic fluctuation of hormones from hypothalamus, anterior pituitary, and ovaries; interact via a negative feedback loop Of note, ovulation is triggered by a positive feedback mechanism 1) Hypothalamus secretes GnRH (gonadotropin-releasing hormone) Stimulates anterior pituitary to release LH and FSH 2) FSH and LH stimulate the follicles to grow and secrete estrogen and inhibin In turn, inhibits the release of more FSH and LH 3) One follicle eventually grows large enough to produce enough estrogens to evert positive feedback on the HPG axis. Results in LH surge and a rise in FSH with triggers ovulation; also transforms ruptured follicle into corpus luteum • Corpus luteum produces progesterone, estrogens and inhibin Will continue to do so until fertilization occurs If no fertilization occurs, progesterone levels drop and cycle repeats. If fertilization occurs: progesterone from corpus luteum inhibits release of gonadotropins continuously for duration of ensuing pregnancy • In absence of fertilization: corpus luteum degenerates into corpus albicans Estrogen, progesterone, and inhibin levels decrease; GnRH levels begin to rise and cycle begins once again.
3. Describe the histology of the uterine wall.
UTERUS (womb) - pathway for sperm to enter uterine tubes; provides a site for newly fertilized ovum to implant itself and where it can be protected and nourished as it develops: • Pear-shaped, hollow organ located in pelvis anterior to rectum and posterior to urinary bladder • Composed of three regions: body (main region), fundus (rounded region superior to entrance to uterine tubes), and cervix (narrow neck) Uterine wall is composed of 3 layers that shed cyclically resulting in menstrual flow: PERIMETRIUM- outermost serous layer is an extension of parietal peritoneum MYOMETRIUM - middle layer composed of bundles of smooth muscle; contract rhythmically during orgasm and childbirth. ENDOMETRIUM - innermost layer that lines uterine cavity; composed of simple columnar epithelium; forms a mucous membrane that rests on a thin layer of connective tissue called lamina propria.
5b. Summarize the stages of oogenesis and include the follicle development that simultaneously occurs.
BEFORE BIRTH: female stem cells called oogonia complete their mitotic division Oogonia begin meiosis I between 3rd and 7th month of fetal development; called primary oocytes Primary oocytes progress as far as prophase I before their development is arrested Primary oocyte develops inside a primordial follicle CHILDHOOD: primary oocytes remain in prophase I and don't develop any further until meiosis resumes after puberty when specific hormone levels trigger initiation of ovarian cycle • Most primordial follicles have died through a process called APOPTOSIS (programmed cellular death) • Some remaining primordial follicles grow into PRIMARY FOLLICLES as oocytes enlarge and develop into SECONDARY FOLLICLES containing arrested primary oocytes. PUBERTY TO MENOPAUSE: Approximately once monthly, 20-30 primary oocytes are stimulated to continue development. One or more primary oocytes complete first meiotic division to produce two haploid cells (1n) that differ in size. Smaller cell contains DNA but little cytoplasm; called first polar body; usually degenerates Larger cell, secondary oocyte, contains DNA and most of cytoplasm; has potential to become an ovum Secondary oocyte proceeds to metaphase II and its development is again arrested One secondary follicle grows into a mature follicle or vesicular follicle (tertiary follicle) about once per month and contains secondary oocyte.
1. List the female reproductive structures including any alternate names for each structure. Describe the functions of each female reproductive structure.
Internal female genitalia include ovaries, uterine tubes, uterus, and vagina • Peritoneum extends down either side of uterus, which creates two regions (pouches) between uterus and urinary bladder and rectum: vesicouterine pouch and rectouterine pouch, respectively. Ovaries - paired female gonads found on lateral walls of pelvic cavity Produce ova Secrete hormones: estradiol, estrone, and estriol, as well as progesterone, inhibin, and relaxin • Anatomical features of each ovary: OVARIAN CORTEX - superficial region where oogenesis (production of gametes) occurs within saclike follicles;develop and mature along with gametes OVARIAN MEDULLA - inner region where blood vessels, lymphatic vessels, and nerves are found. Each ovary is held in place by three ligaments that provide structural support: BROAD LIGAMENT - large, flat ligament that attaches to ovaries, uterine tubes, and uterus, connecting these structures to bony pelvis OVARIAN LIGAMENT - connects medial surface of ovary to uterus, near attachment of uterine tube SUSPENSORY LIGAMENT (infundibulopelvic ligament) -connects lateral surface of ovary to pelvic wall and provides support for ovarian artery and vein.Uterine tubes (fallopian tubes, or oviducts) form initial segment of reproductive system Moves oocytes toward uterus Site of fertilization and early stages of development Four regions: AMPULLA, INFUNDIBILUM, FIMBRIAE, ISTHMUS
13a. Define menopause and describe the effects of menopause on the female body. Define atresia.
MENOPAUSE - point when menstruation has not occurred for at least one year. Menopause occurs because: Number of primary follicles left that can respond to LH and FSH is diminished after thirty or more years of ovarian cycles. ATRESIA - process in which immature follicles degenerate and are resorbed during follicular phase of menstrual cycle. Reduced levels of estrogens and progesterone may alter female secondary sex characteristics. Breasts, uterus, and uterine tubes may shrink, while pubic and axillary hair may thin. Bone density may decrease; increases risk of developing osteoporosis. Vasomotor signs that include "hot flashes" may occur due to changes in rhythmic secretion of GnRH by hypothalamus in response to decreasing blood levels of sex hormones. Women may experience many other nonspecific symptoms, including migraine headaches, backaches, fatigue, and mood swings. • Early menopause is occurrence of menopause before age of 45, while premature menopause occurs before age of 40.
8. Describe the structure and function of the endometrial layers. Explain the endometrial glands and the blood supply to the endometrium.
Uterine cycle (menstrual cycle) - series of cyclic events that uterine endometrium goes through each month in response to fluctuating levels of ovarian hormones Uterine changes are coordinated with estrogen and progesterone levels released during ovarian cycle Under control of gonadotropins released from anterior pituitary Endometrium is composed of two main layers (strata): STRATUM FUNCTIONALIS: (functional layer) is location of cyclic change in response to fluctuating hormone levels o Stratum functionalis detaches from uterine wall and is shed with a discharge of 35-50 ml of blood and other materials from vagina, usually monthly during menstruation Thinner, deeper layer is STRATUM BASALIS (basal layer); does not thicken in response to hormone fluctuations, nor is it shed during menstruation, but it replaces stratum functionalis at end of menstruation. Endometrium also contains many endometrial (uterine) glands that change in length as endometrial thickness increases. Glands will produce uterine milk • Main uterine vascular supply is from uterine arteries; branches from internal iliac arteries in pelvis • Uterine arteries terminate in stratum functionalis as spiral (coiled) arteries These arteries respond to hormonal changes and lead to loss of blood supply to endometrium.
9. Describe the 3 phases of the uterine, or menstrual, cycle.
Uterine cycle proceeds through three phases during an average of 28 days Menstrual phase, days 1-5 o Uterus sheds stratum functionalis, resulting in menstruation Proliferative (preovulatory) phase, days 6-14 o A new stratum functionalis is generated with endometrial glands, spiral arteries, and veins; o Stratum functionalis begins to thicken (proliferate) o Glands enlarge and veins and arteries increase in number o Ovulation occurs around day 14 Secretory phase, days 15-28 o Spiral arteries convert stratum functionalis into secretory mucosa and endometrial glands secrete nutritious glycogen-rich fluid (uterine milk) o If pregnancy doesn't occur, cells of stratum functionalis die and on day 28 menstrual phase begins o If pregnancy occurs, secretory phase continues and uterus continues to develop in preparation for an embryo.
4. Describe the histology of the vagina.
VAGINA - organ of copulation; receives penis and semen during sexual intercourse; passageway for giving birth and for menstrual flow • Thick-walled tube that extends from cervix to exterior of body • Parallel to urethra; lies between urinary bladder and rectum. • Vaginal wall is lined with transverse ridges called rugae; stimulate penis during intercourse • Vaginal mucosa is composed of stratified squamous epithelium; able to withstand frictional forces; mucus from cervix provides lubrication Epithelial cells secrete glycogen into vaginal lumen; metabolized by resident bacteria; generates lactic acid that helps maintain acidic pH of this region HYMEN - vascular partition of mucosa near distal vaginal orifice; commonly ruptured during first sexual intercourse. Vulva - external reproductive structures SEE FIGURE 26.2!!
