Female Reproductive System Notes

Sexual Differentiation

• Initially, the two sexes appear indistinguishable during the first 8 to 10 weeks of development. This undifferentiated stage is crucial.

• The development of the female reproductive tract from the paramesonephric ducts occurs due to the absence of testosterone and müllerian-inhibiting factor (MIF). This process isn't driven by a specific female hormone but rather the lack of male hormones.

• Without testosterone:

  • Mesonephric ducts, which could potentially develop into male reproductive structures, degenerate.

  • The genital tubercle differentiates into the glans clitoris, a highly sensitive structure.

  • Urogenital folds develop into the labia minora, the inner lips of the vulva.

  • Labioscrotal folds develop into the labia majora, the outer lips of the vulva.

• Without MIF, the paramesonephric ducts develop into the uterine tubes (fallopian tubes), uterus, and the upper portion of the vagina. MIF's absence is critical for the proper formation of these structures.

The Genitalia

• Internal genitalia in females include the ovaries, uterine tubes, uterus, and vagina. These organs are crucial for reproduction and hormone production.

• External genitalia include the clitoris, labia minora, and labia majora, which play roles in sexual function and protection.

• These structures are located within the perineum, the region between the pubic symphysis and the coccyx.

• Primary sex organs: Ovaries, responsible for producing egg cells and sex hormones.

• Secondary sex organs: Other internal and external genitalia that support reproduction.

The Ovaries

• Ovaries are the female gonads that produce egg cells (ova) through oogenesis and synthesize sex hormones, including estrogen and progesterone.

• Almond-shaped, they are located in the ovarian fossa on the posterior pelvic wall.

• The ovary is encapsulated by a tunica albuginea, a fibrous connective tissue layer similar to that in the testes.

• Outer cortex: Contains follicles where germ cells (oocytes) develop.

• Inner medulla: Composed of major arteries, veins, and connective tissue.

• Each egg cell develops within its own fluid-filled follicle, which supports its maturation.

• Ovulation: The process where the follicle bursts, releasing the mature egg (ovum).

Ligaments of Ovary

• The ovary is attached to the uterus via the ovarian ligament.

• It is connected to the pelvic wall by the suspensory ligament, which carries the ovarian artery, vein, and nerves. This is the main neurovascular supply to the ovary.

• The mesovarium, a fold of the broad ligament, anchors the ovary.

• The ovary receives its blood supply from two main arteries:

  • Ovarian branch of the uterine artery

  • Ovarian artery, which is analogous to the testicular artery in males.

The Ovaries - Blood Supply

• The ovarian and uterine arteries anastomose along the margin of the ovary, providing a redundant blood supply. Small arterial branches then enter the ovary.

• Ovarian veins, lymphatics, and nerves also traverse the suspensory ligaments, ensuring proper function and drainage.

The Uterine Tubes

• Uterine tube (oviduct or fallopian tube):

• A canal approximately 10 cm long extending from the ovary to the uterus.

• The muscular tube is lined with ciliated cells and is highly folded into longitudinal ridges, which help in the transport of the oocyte.

• Major portions:

  • Infundibulum: The flared, trumpet-shaped distal (ovarian) end that captures the oocyte after ovulation.

  • Fimbriae: Feathery projections on the infundibulum that help guide the oocyte into the tube.

  • Ampulla: The middle and longest part, where fertilization typically occurs.

  • Isthmus: The narrower end closer to the uterus.

  • Mesosalpinx: The superior part of the broad ligament that supports and enfolds the uterine tube.

The Uterus

• The uterus is a thick, muscular chamber opening into the roof of the vagina.

• Typically, it tilts forward over the urinary bladder (anteverted and anteflexed).

• The uterus harbors the fetus during pregnancy, provides nutrition, and expels the fetus at the end of gestation.

• Pear-shaped organ:

  • Fundus: Broad, superior curvature.

  • Body (corpus): Main, middle portion.

  • Cervix: Cylindrical, inferior end.

• The lumen is roughly triangular with openings to the uterine tubes at the upper corners and the internal os at the lower apex.

• It is a potential space in the nonpregnant uterus rather than a hollow cavity.

• Cervical canal: Connects the uterine lumen to the vagina.

  • Internal os: Superior opening into the uterine body.

  • External os: Inferior opening into the vagina.

• Cervical glands: Secrete mucus to prevent the spread of microorganisms from the vagina to the uterus, offering protection against infection.

Pap Smears and Cervical Cancer

• Cervical cancer commonly affects women between 30 and 50 years of age.

• Risk factors include smoking, early sexual activity, STDs, and human papillomavirus (HPV) infection.

• Typically originates in the epithelial cells of the lower cervix.

• Early detection through Pap smears is the best protection. Cells are collected from the cervix and vagina and examined microscopically for abnormalities.

• Three grades of cervical intraepithelial neoplasia (CIN):

  • Class I: Mild dysplasia, often resolving spontaneously.

  • Class II: Requires biopsy for further evaluation.

  • Class III: May necessitate radiation therapy or hysterectomy, depending on severity.

Uterine Wall

• Perimetrium: The external serosa layer providing protection.

• Myometrium: The thick, middle muscular layer forming most of the uterine wall.

  • Composed mainly of smooth muscle, enabling powerful contractions.

  • Smooth muscle sweeps downward from the fundus and spirals around the body.

    • Less muscular and more fibrous near the cervix, providing structural support.

  • Responsible for labor contractions during childbirth and expelling the fetus.

• Endometrium: The inner mucosa consisting of simple columnar epithelium, compound tubular glands, and a stroma populated with leukocytes and macrophages.

  • Functional layer (stratum functionalis): The superficial half that is shed during each menstrual period in response to hormonal changes.

  • Basal layer (stratum basalis): The deep layer that remains and regenerates the stratum functionalis with each menstrual cycle.

  • During pregnancy, the endometrium serves as the site for embryo attachment and forms the maternal part of the placenta, providing fetal nourishment.

Uterus Support

• The uterus is supported by the muscular floor of the pelvic outlet and peritoneal folds that form ligaments.

• The broad ligament comprises the mesosalpinx and mesometrium on each side of the uterus, providing wide support.

• Cardinal (lateral cervical) ligaments: Support the cervix and the superior part of the vagina, extending to the pelvic wall for stability.

• Uterosacral ligaments: Attach the posterior uterus to the sacrum, providing posterior support.

• Round ligaments: Originate from the anterior uterus, pass through the inguinal canals, and terminate in the labia majora, similar to the gubernaculum in males.

Uterine Blood Supply

• The uterine blood supply is essential for the menstrual cycle and pregnancy, providing nutrients and oxygen.

• The uterine artery arises from the internal iliac artery.

  • It branches to penetrate the myometrium, leading to arcuate arteries.

  • These arteries encircle the uterus and anastomose with their counterparts on the opposite side.

• Spiral arteries penetrate the myometrium into the endometrium.

  • They wind between endometrial glands toward the mucosal surface.

  • These arteries rhythmically constrict and dilate in response to hormones, causing the endometrium to blanch and flush with blood.

The Vagina

• Vagina (birth canal): An 8 to 10 cm long distensible muscular tube.

• Functions include the discharge of menstrual fluid, reception of the penis and semen, and passage of the baby during childbirth.

• Consists of an outer adventitia, a middle muscularis, and an inner mucosa.

• Tilted posteriorly between the rectum and urethra.

• The vagina lacks glands; lubrication is provided by transudation (vaginal sweating) and cervical mucus.

• Transudation lubricates the vagina through serous fluid passing through its walls and mucus from the cervical gland above it.

• Fornices: Blind-ended spaces at the top of the vagina that extend beyond the cervix.

• Transverse friction ridges (vaginal rugae) are present at the lower end.

• Mucosal folds form the hymen across the vaginal opening.

• Vaginal epithelium:

  • Undergoes metaplasia, transforming from one tissue type to another.

  • Childhood: Simple cuboidal epithelium.

    • Puberty: Estrogens cause it to transform into stratified squamous epithelium for protection.

  • Bacteria ferment glycogen, creating an acidic pH that inhibits pathogen growth.

  • Contains antigen-presenting dendritic cells, a route for HIV from infected semen to invade the female body.

The External Genitalia

• The external genitalia, collectively termed the vulva or pudendum, includes:

• Mons pubis: A mound of fat over the pubic symphysis bearing most of the pubic hair.

• Labia majora: Pair of thick folds of skin and adipose tissue inferior to the mons.

• Pudendal cleft: The fissure between the labia majora.

• Labia minora: Thin, hairless folds medial to the labia majora.

• The space between the labia minora forms the vestibule, containing the urethral and vaginal openings.

• The anterior margins of the labia minora join to form a hood-like prepuce over the clitoris.

Vulva

• Clitoris: An erectile, sensory organ and the primary center for sexual stimulation.

  • Consists of a glans, body, and crura.

• Vestibular bulbs: Erectile tissue deep to the labia majora that brackets the vagina.

• Greater and

  Typically begins around age 8-10 in girls in the United States and may be influenced by genetic, environmental, and health-related factors. The timing can vary significantly among individuals.

• Triggered by rising levels of Gonadotropin-Releasing Hormone (GnRH) from the hypothalamus, which then acts on the pituitary gland.

  • GnRH neurons in the hypothalamus increase their pulsatile secretion, which is crucial for stimulating the release of gonadotropins.

  • The activation of GnRH secretion can be affected by factors such as nutrition, body fat, and stress levels.

  • Kisspeptin, a neuropeptide, plays a key role in the activation of GnRH neurons.

  • Disruptions in GnRH signaling can lead to delayed or precocious puberty.

• GnRH stimulates the anterior pituitary to secrete Follicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH).

  • FSH and LH are essential for the development of ovarian follicles, the production of sex hormones, and the regulation of the menstrual cycle.

  • The pulsatile release of GnRH is critical for the differential secretion of FSH and LH.

• FSH stimulates ovarian follicles, which then secrete:

  • Estrogen (primarily estradiol, estriol, and estrone).

    • Estradiol is the most potent and abundant estrogen, influencing the development of secondary sexual characteristics and the reproductive system.

    • Estriol is mainly produced during pregnancy.

    • Estrone can be converted to estradiol and is the predominant estrogen after menopause.

  • Progesterone.

    • Progesterone prepares the uterus for implantation and supports pregnancy by maintaining the uterine lining.

    • It also has effects on the brain, influencing mood and behavior.

  • Inhibin.

    • Inhibin selectively suppresses FSH secretion, providing negative feedback to regulate follicle development.

  • A small amount of androgen.

    • Androgens, such as testosterone and androstenedione, are precursors for estrogen synthesis and contribute to the development of pubic and axillary hair.

• Estrogens are feminizing hormones with widespread effects on the body.

  • They promote the development of female secondary sexual characteristics, such as breast development and widening of the hips.

  • Estrogens affect bone density, cardiovascular health, and cognitive function.

• Estrogens and progesterone exert negative feedback on FSH and LH secretion.

  • This feedback loop helps maintain hormonal balance and regulates the menstrual cycle.

• Inhibin selectively suppresses FSH secretion.

  • Inhibin provides a direct negative feedback on the pituitary, fine-tuning FSH levels and influencing follicle selection.

• Hormone secretion is distinctly cyclic, with hormones secreted in a specific sequence.

  • The cyclic pattern of hormone secretion regulates the menstrual cycle, influencing ovulation and the preparation of the uterus for pregnancy.

Key Puberty Events

• Thelarche: Onset of breast development (earliest visible sign).

  • Estrogen, progesterone, and prolactin stimulate the development of ducts and lobules in the breasts.

    • Estrogen stimulates the growth of the ductal system.

    • Progesterone promotes the development of lobules and alveoli.

    • Prolactin, though more significant during pregnancy and lactation, contributes to early breast development.

  • Glucocorticoids and growth hormone govern the completion of duct and lobule formation.

    • Growth hormone regulates overall breast size and structure.

    • Glucocorticoids modulate the growth and differentiation of mammary tissue.

  • Adipose and fibrous tissue contribute to breast enlargement.

    • Fat deposition is influenced by genetics, nutrition, and hormonal factors.

    • Fibrous tissue provides structural support.

• Pubarche: Appearance of pubic and axillary hair, sebaceous glands, and axillary glands.

  • Androgens from the ovaries and adrenal cortex stimulate pubarche and libido.

    • DHEA-S (dehydroepiandrosterone sulfate) from the adrenal glands plays a significant role in the initial development of pubic and axillary hair.

    • Ovarian androgens contribute to the maintenance and further development of these secondary sexual characteristics.

• Menarche: First menstrual period.

  • Requires a minimum of 17% body fat in teenagers.

    • Body fat is crucial for the production of leptin, which influences GnRH secretion.

  • Improved nutrition has lowered the average onset age to around 12.

    • Adequate nutrition supports overall growth and hormonal balance, leading to earlier menarche.

  • Leptin stimulates gonadotropin secretion.

    • Leptin signals the hypothalamus about the body's energy stores, impacting reproductive function.

  • If body fat and leptin levels drop too low, gonadotropin secretion declines, potentially causing the menstrual cycle to cease.

    • Conditions like anorexia nervosa can lead to amenorrhea due to insufficient body fat and leptin levels.

  • Menstruation may cease if body fat drops below 22% in adult women.

    • This threshold ensures sufficient energy reserves for reproductive function.

  • The first few menstrual cycles are often anovulatory (no egg is ovulated).

    • Hormonal imbalances and incomplete maturation of the hypothalamic-pituitary-ovarian axis can cause anovulatory cycles.

  • Girls typically begin ovulating regularly about a year after menarche.

    • This marks the establishment of regular, ovulatory menstrual cycles.

Effects of Estradiol and Progesterone

• Estradiol stimulates:

  • Vaginal metaplasia.

    • Induces the transformation of the vaginal epithelium to a non-keratinized, stratified squamous epithelium.

  • Growth of ovaries and secondary sex organs.

    • Promotes the development of the uterus, fallopian tubes, and other reproductive structures.

  • Growth hormone secretion, leading to an increase in height and widening of the pelvis.

    • Estrogen enhances growth hormone release, affecting skeletal growth and body composition.

  • Fat deposition in breasts and hips.

    • Influences the distribution of subcutaneous fat, contributing to female body contours.

  • Thickening of the skin (though girls' skin remains thinner, softer, and warmer than boys').

    • Affects collagen production and skin hydration, resulting in characteristic differences in skin texture.

• Progesterone primarily prepares the uterus for potential pregnancy during the second half of the menstrual cycle.

  • It promotes the development of the uterine lining, making it receptive to implantation.

  • Progesterone also has a role in preventing uterine contractions during pregnancy.

Climacteric and Menopause

• Climacteric: Midlife change in hormone secretion.

  • Accompanied by menopause (cessation of menstruation).

    • Transition phase that can last several years, marked by fluctuating hormone levels and various symptoms like hot flashes, mood changes, and sleep disturbances.

  • A female is born with approximately 2 million eggs; climacteric begins when about 1,000 follicles remain.

    • The depletion of ovarian follicles leads to decreased estrogen production.

  • Remaining follicles become less responsive to gonadotropins and secrete less estrogen and progesterone.

    • Reduced hormone production causes a range of physiological changes.

  • This leads to atrophy of the uterus, vagina, and breasts.

    • Estrogen deficiency results in thinning of the vaginal lining, decreased uterine size, and reduced breast tissue.

• Menopause: Cessation of menstrual cycles.

  • Usually occurs between ages 45 and 55.

    • Influenced by genetic, lifestyle, and health factors.

  • Menopause is considered complete after one year without menstruation.

    • Confirmed by the absence of menstrual bleeding for 12 consecutive months.

Reproductive and Sexual Cycles

• Reproductive cycle: Sequence of events from fertilization to giving birth and returning to fertility.

  • Encompasses pregnancy, childbirth, and the postpartum period, during which the body returns to its pre-pregnancy state.

• Sexual cycle: Recurring monthly events when pregnancy does not occur.

  • Involves two interrelated cycles controlled by shifting hormone secretion patterns:

    • Ovarian cycle: Events in the ovaries.

      • Follicle development, ovulation, and corpus luteum formation.

    • Menstrual cycle: Parallel changes in the uterus.

      • Endometrial buildup, shedding, and regeneration.

Oogenesis

• Oogenesis: Egg production.

  • Produces haploid gametes via meiosis.

    • Meiosis reduces the chromosome number from diploid (46) to haploid (23), ensuring the correct chromosome number in the zygote after fertilization.

  • A cyclic event typically releasing one egg each month.

    • Ovulation usually occurs once per menstrual cycle.

  • Accompanied by cyclic changes in hormone secretion and histological structure of the ovaries and uterus.

    • Hormonal fluctuations regulate follicle development, ovulation, and endometrial changes.

  • Uterine changes result in monthly menstrual flow.

    • Menstruation occurs when the uterine lining is shed due to hormonal withdrawal.

Embryonic Development of the Ovary

• Female germ cells originate in the yolk sac.

  • Primordial germ cells migrate from the yolk sac to the developing gonads.

• They colonize the gonadal ridges during the first 5-6 weeks of development.

  • The gonadal ridges differentiate into ovaries under the influence of genes like DAX1 and WNT4.

• Germ cells differentiate into oogonia, multiplying until the fifth month, reaching 6 to 7 million in number.

  • Oogonia proliferate through mitosis.

• Oogonia transform into primary oocytes, initiating early meiosis I.

  • Primary oocytes enter prophase I of meiosis but arrest at this stage until puberty.

• Most primary oocytes degenerate (atresia) before birth, leaving approximately 2 million at birth.

  • Atresia is a process of programmed cell death that eliminates many oocytes.

• Egg/ovum: any stage from primary oocyte to fertilization.

  • Represents the entire developmental timeline of the female gamete.

• By puberty, approximately 200,000 oocytes remain.

  • The number of oocytes declines throughout life.

• Lifetime supply: A female will likely ovulate around 480 times.

  • Only a small fraction of oocytes are ovulated during a woman's reproductive years.

Egg Development in Adolescence

• FSH stimulates ONLY one oocyte from a monthly cohort of about 24 primary oocytes to complete meiosis I.

  • FSH promotes the growth and development of ovarian follicles.

• The primary oocyte divides into two haploid daughter cells of unequal size:

  • Secondary oocyte: The larger daughter cell. Product of meiosis I.

    • Contains most of the cytoplasm and cellular organelles.

  • First polar body: The smaller cell, which ultimately disintegrates (a mechanism for discarding extra haploid chromosomes).

    • Serves to eliminate extra chromosomes, ensuring the secondary oocyte is haploid.

• The secondary oocyte proceeds to metaphase II and arrests until after ovulation.

  • The secondary oocyte pauses in meiosis II until fertilization occurs.

• If not fertilized, it dies without finishing meiosis.

  • Without fertilization, the secondary oocyte degenerates.

• If fertilized, it completes meiosis II, casting off a second polar body.

  • Fertilization triggers the completion of meiosis II.

• The chromosomes of the remaining large egg unite with those of the sperm.

  • Forms a diploid zygote, the first cell of the new organism.

Comparison of Spermatogenesis and Oogenesis

Key differences in gametogenesis:

• Spermatogenesis creates 4 cells with an equal distribution of cytoplasm.

  • Results in four viable sperm cells.

• Oogenesis creates 1 cell with an unequal distribution of cytoplasm.

  • Produces one viable egg and polar bodies.

Folliculogenesis

• Folliculogenesis: Development of the follicles around the egg that undergoes oogenesis.

Primordial Follicles

• Consist of a primary oocyte in early meiosis, surrounded by a single layer of squamous follicular cells.

  • The basic structural unit of the ovary, housing the primary oocyte.

• Follicular cells connect to the primary oocyte via cytoplasmic processes for nutrient and signal exchange.

  • Facilitates communication and support between follicular cells and the oocyte.

• Concentrated in the cortex of the ovary.

  • Located in the outer layer of the ovary.

• Remain in this state for 13 to 50 years before further development

  • The quiescent phase can last for a significant portion of a woman's life.

• Adult ovary: 90-95% are primordial follicles.

  • The vast majority of follicles are in this resting stage.

• Monthly recruitment of about 24 follicles, beginning a 290-day path to maturity, but only one will finish.

  • Only one follicle typically reaches ovulation each month.

Follicle Development Stages

• Primary Follicles:

  • About 140 days into the cycle, recruited primordial follicles become primary follicles.

  • Contain larger, primary oocytes and a surrounding layer of cuboidal follicular cells.

• Secondary Follicles:

  • Appear about 170 days into the cycle.

  • Primary oocytes are even larger, and follicular cells now form two or more layers (granulosa cells).

  • Zona pellucida: A layer of glycoprotein gel secreted by the primary oocyte.

    • Protects the oocyte and plays a role in fertilization.

  • Theca folliculi: Connective tissue around the granulosa cells condenses to form a fibrous husk.

    • Provides structural support and endocrine function.

    • Theca externa: Outer fibrous capsule, rich in blood vessels.

      • Supplies blood to the follicle.

    • Theca interna: Inner cellular, hormone-secreting layer. Produces androgens (androstenedione and testosterone), which granulosa cells convert to estradiol.

      • Produces androgens that serve as precursors for estrogen synthesis in the granulosa cells.

• Tertiary Follicles:

  • Appear about 230 days into the cycle, approximately 60 days before ovulation.

  • Granulosa cells begin secreting follicular fluid, forming small pools.

  • As pools enlarge, they merge, forming a single antrum.

    • Antrum: Fluid-filled cavity that characterizes tertiary follicles.

    • Antral follicles: Tertiary and mature follicles.

    • Preantral follicles: Earlier stages of follicle development.

  • Cumulus oophorus: A mound of granulosa cells on one side of the antrum, covering and securing the primary oocyte to the follicular wall.

    • Supports and nourishes the oocyte.

  • Corona radiata: Innermost layer of cells in the cumulus, surrounding the zona pellucida and primary oocyte. Forms a protective barrier around the egg.

    • Provides protection and support to the oocyte as it is released during ovulation.

• Mature Follicles:

  • About 10 days before ovulation, one follicle becomes dominant (destined to ovulate) while the rest degenerate.

  • The dominant follicle captures and holds FSH, growing rapidly.

  • About 5 days before ovulation, it is large enough to be considered a preovulatory (Graafian) follicle.

  • An LH surge induces completion of Meiosis I, generating the secondary oocyte and first polar body, followed by ovulation.

The Sexual Cycle

• Averages 28 days, varying from 20-45 days.

  • Cycle length varies among individuals and can be influenced by various factors.

• The hypothalamus regulates the pituitary gland.

  • The hypothalamus secretes GnRH, which controls the pituitary gland's hormone secretion.

• Pituitary hormones regulate the ovaries.

  • FSH and LH from the pituitary stimulate follicle development and hormone production in the ovaries.

• Ovaries secrete hormones that regulate the uterus.

  • Estrogen and progesterone from the ovaries affect the uterine lining.

• Basic hierarchy of hormonal control: Hypothalamus → pituitary → ovaries → uterus.

• Ovaries exert feedback control over the hypothalamus and pituitary.

  • Hormones produced by the ovaries provide negative feedback, regulating the hypothalamus and pituitary.

Ovarian Cycle

• Three principal steps: follicular phase, ovulation, and luteal phase.

Follicular Phase

• Begins with a 2-week follicular phase.

  • Menstruation occurs during the first 3-5 days.

    • The uterus replaces lost tissue via mitosis, and a cohort of follicles grows.

  • Ovulation occurs around day 14.

  • The remainder of the follicle becomes the corpus luteum.

• Next 2 weeks: luteal phase

  • Corpus luteum stimulates endometrial secretion and thickening.

  • If pregnancy does not occur, the endometrium breaks down in the last 2 days.

  • Menstruation begins, and the cycle restarts.

• Extends from the beginning of menstruation until ovulation (Days 1-14).

  • Includes the preovulatory phase: the end of menstruation until ovulation.

    • The most variable part of the cycle; ovulation is seldom predictable.

  • FSH stimulates follicles to grow and secrete estradiol.

  • The dominant follicle becomes increasingly sensitive to FSH, LH, and estradiol.

• The dominant follicle has a rich blood supply and a large number of FSH receptors, becoming the preovulatory follicle.

• Other antral follicles degenerate (atresia).

• The ovary also contains follicles at earlier stages for maturation in future cycles.

Ovulation

• Rupture of the mature follicle and release of the egg and attendant cells, typically around day 14.

• Estradiol stimulates a surge of LH and a lesser spike of FSH by the anterior pituitary.

• LH induces several events:

  • The primary oocyte completes meiosis I, producing the secondary oocyte and first polar body.

  • Follicular fluid builds rapidly, and the follicle swells (resembling a blister on the ovary).

  • Macrophages and leukocytes secrete enzymes that weaken the follicle wall.

  • A nipple-like stigma appears on the surface.

Ovulation Details

• Takes only 2-3 minutes.

• The stigma seeps follicular fluid for 1-2 minutes.

• The follicle bursts, and the remaining fluid oozes out, carrying the secondary oocyte and cumulus oophorus.

• Normally swept up by ciliary current and taken into the uterine tube.

• The uterine tube prepares to catch the oocyte, swelling with edema.

• Its fimbriae envelop and caress the ovary in synchrony with the woman’s heartbeat.

• Cilia creates a gentle current in nearby peritoneal fluid.

Signs of Ovulation

• Cervical mucus becomes thinner and more stretchy.

  • Facilitates sperm transport.

• Resting body temperature rises 0.4 to 0.6°F.

  • Best measured first thing in the morning before getting out of bed.

  • Record for several days to see the difference.

• Mittelschmerz: twinges of pain at the time of ovulation.

  • Caused by follicular swelling or rupture.

• Best time for conception:

  • Within 24 hours after the cervical mucus changes and the basal temperature rises.

Luteal Phase

• Postovulatory phase: Day 15 to day 28, from just after ovulation to the onset of menstruation.

• If pregnancy does not occur:

  • The follicle ruptures, collapses, and bleeds into the antrum.

  • Clotted blood is slowly absorbed.

  • Granulosa and theca interna cells multiply and fill the antrum.

  • A dense bed of capillaries grows amid them.

  • The ovulated follicle becomes the corpus luteum.

• Named for the yellow lipid accumulating in the theca interna cells, now called lutein cells.

Corpus Luteum Regulation

• Transformation from ruptured follicle to corpus luteum is regulated by LH.

• LH stimulates the corpus luteum to grow and secrete rising levels of estradiol and progesterone.

  • A 10-fold increase in progesterone is the most important aspect of the luteal phase.

  • Progesterone is crucial in preparing the uterus for the possibility of pregnancy.

• LH and FSH secretion decline over the rest of the cycle.

• High levels of estradiol and progesterone, along with inhibin from the corpus luteum, have a negative feedback effect on the pituitary.

• The corpus luteum begins involution (shrinkage) around day 22 (8 days after ovulation).

• By day 26, involution is complete, and the corpus luteum becomes the corpus albicans: small scar.

• With diminishing ovarian steroid secretion, FSH levels rise, ripening a new cohort of follicles.

• Ovulation occurs in one ovary per cycle, with the two ovaries usually alternating monthly.

• The ovulated oocyte began ripening 290 days earlier and began development before birth.

The Menstrual Cycle

• Consists of the buildup of the endometrium during most of the sexual cycle, followed by its breakdown and vaginal discharge.

• Divided into four phases: proliferative phase, secretory phase, premenstrual phase, and menstrual phase.

• The first day of noticeable vaginal discharge is defined as day 1 of the sexual cycle.

• Menstrual phase average: 5 days.

Phases of the Menstrual Cycle

• Proliferative Phase:

  • Rebuilding of the functional layer of the endometrium that was lost in the last menstruation.

  • At day 5 of menstruation, the endometrium is about 0.5 mm thick and consists only of the basal layer.

  • As a new cohort of follicles develops, they secrete more estrogen.

  • Estrogen stimulates mitosis in the basal layer and regrowth of blood vessels to regenerate the functional layer.

  • By day 14, the endometrium is 2 to 3 mm thick.

  • Estrogen also stimulates endometrial cells to produce progesterone receptors.

• Secretory Phase:

  • The endometrium thickens more in response to progesterone from the corpus luteum (Day 15 to day 26).

  • Thickening results from secretion and fluid accumulation rather than mitosis.

  • Endometrial glands secrete glycogen.

  • Glands grow wider, longer, and more coiled.

  • The endometrium is 5 to 6 mm thick.

  • A soft, wet, nutritious bed is available for embryonic development.

• Premenstrual Phase:

  • A period of endometrial degeneration during the last 2 days of the cycle.

  • The corpus luteum atrophies, and progesterone levels fall.

  • This triggers spasmodic contractions of spiral arteries, causing endometrial ischemia (interrupted blood flow).

  • This brings about tissue necrosis and menstrual cramps.

  • Pools of blood accumulate in the functional layer.

  • Necrotic endometrium mixes with blood and serous fluid, forming menstrual fluid.

• Menstrual Phase (Menses):

  • Discharge of menstrual fluid from