Overview of Female Cycles and Folliculogenesis
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Overview of Female Cycles and Folliculogenesis

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Questions and Answers

What is the primary hormone responsible for initiating ovulation?

  • Progesterone
  • Follicle-stimulating hormone (FSH)
  • Luteinizing hormone (LH) (correct)
  • Estrogen

    • What happens to the corpus luteum if pregnancy does not occur?

  • It degenerates to form a fibrous clot (correct)
  • It persists for 3 months before degeneration
  • It transforms into a primordial follicle
  • It continues to secrete progesterone indefinitely

    • During which phase does a primary oocyte complete its first mitotic division?

  • Preovulatory phase (correct)
  • Follicular phase
  • Luteal phase
  • Primordial phase

    • How long does it generally take for a primordial follicle to mature into an ovulatory follicle?

    <p>Around 6 months or longer</p> Signup and view all the answers

    What connects the cumulus oophorus to the secondary oocyte after its separation?

    <p>The corona radiata</p> Signup and view all the answers

    During which phase does the stratum functionalis undergo rebuilding from 2-8mm in thickness?

    <p>Proliferative / Preovulatory Phase</p> Signup and view all the answers

    What primary hormonal changes promote the expression of progesterone receptors on endometrial cells?

    <p>Increased levels of plasma oestrogen</p> Signup and view all the answers

    Which histological feature indicates the secretory phase of the endometrium?

    <p>Sawtooth and coiled glands with abundant secretory products</p> Signup and view all the answers

    How does the rapid increase in progesterone during the secretory phase affect the cervical mucus?

    <p>It thickens the mucus, forming a barrier to sperm and bacteria.</p> Signup and view all the answers

    What occurs if fertilization does not take place after the secretory phase?

    <p>Blood enters fragmented capillaries leading to menses.</p> Signup and view all the answers

    What is the primary role of progesterone in the menstrual cycle?

    <p>Thicken cervical mucus and inhibit uterine contractions</p> Signup and view all the answers

    Which phase of the menstrual cycle involves the shedding of the stratum functionalis?

    <p>Menstrual phase</p> Signup and view all the answers

    Which hormone indicates ovarian reserve and decreases with age?

    <p>Anti Mullerian Hormone (AMH)</p> Signup and view all the answers

    During which menstrual phase do spiral arterioles dilate, leading to hemorrhaging?

    <p>Menstrual phase</p> Signup and view all the answers

    What effect does an increase in prostaglandins have during the menstrual phase?

    <p>Cause uterine contractions and vasoconstriction</p> Signup and view all the answers

    What role do theca cells play in the production of oestrogen?

    <p>They produce androgens under the influence of LH.</p> Signup and view all the answers

    Over what time period does it typically take for a primordial follicle to mature into an ovulatory follicle?

    <p>More than 6 months.</p> Signup and view all the answers

    Which of the following statements most accurately describes early antral follicles?

    <p>They have small antrums and develop along with pre-antral follicles.</p> Signup and view all the answers

    What happens to the number of pre-antral and early antral follicles at the start of each menstrual cycle?

    <p>10-25 pre-antral and early antral follicles develop into larger antral follicles.</p> Signup and view all the answers

    Which factor is critical in determining which follicle continues to develop into a dominant follicle?

    <p>Amount of local oestrogen within the follicle.</p> Signup and view all the answers

    Which of the following best describes an antral follicle?

    <p>It features a singular large antrum.</p> Signup and view all the answers

    Which hormone is primarily involved in the conversion of androgens to oestrogen in granulosa cells?

    <p>Follicle-stimulating hormone (FSH).</p> Signup and view all the answers

    Which statement is false regarding the presence of follicles in the ovaries?

    <p>The ovaries contain only mature follicles after puberty.</p> Signup and view all the answers

    What does low concentration of oestrogen primarily affect in the ovarian and menstrual cycle?

    <p>Inhibits FSH and LH release</p> Signup and view all the answers

    Which hormone is primarily responsible for the surge that causes ovulation?

    <p>Luteinizing Hormone (LH)</p> Signup and view all the answers

    What happens to the corpus luteum if there is no pregnancy?

    <p>It degenerates, leading to a decrease in progesterone and oestrogen</p> Signup and view all the answers

    How does high concentration of oestrogen affect the release of FSH and LH?

    <p>It causes a positive feedback mechanism for their release</p> Signup and view all the answers

    What role do granulosa cells play in the ovarian cycle?

    <p>They produce oestrogen as the follicle grows</p> Signup and view all the answers

    What indicates the beginning of the secretory phase in the menstrual cycle?

    <p>The increase of progesterone from the corpus luteum</p> Signup and view all the answers

    What physiological change occurs in the endometrium due to progesterone release?

    <p>It becomes secretory</p> Signup and view all the answers

    Which of the following best describes the relationship between FSH and LH during the menstrual cycle?

    <p>FSH aids in follicle growth while LH triggers ovulation</p> Signup and view all the answers

    What occurs when there is a decrease in progesterone and oestrogen levels?

    <p>Menstruation occurs due to lack of endometrial support</p> Signup and view all the answers

    Which phase of the ovarian cycle is primarily responsible for follicle growth?

    <p>Follicular phase</p> Signup and view all the answers

    How long does it generally take for a primordial follicle to mature into an ovulatory follicle?

    <blockquote> <p>6 months</p> </blockquote> Signup and view all the answers

    What structure is formed from the primary follicle during its development?

    <p>Zona pellucida</p> Signup and view all the answers

    Which statement best describes the presence of early antral and pre-antral follicles?

    <p>They remain constant from puberty until menopause</p> Signup and view all the answers

    What event marks the completion of the first mitotic division of the primary oocyte?

    <p>Transformation into a secondary oocyte</p> Signup and view all the answers

    Which of the following accurately describes the fate of the corpus luteum if pregnancy does not occur?

    <p>It forms a fibrous clot and degenerates after 10 days</p> Signup and view all the answers

    What is the primary outcome of the ballooning of the follicle and ovary during ovulation?

    <p>The stigma site ruptures, expelling the oocyte into the peritoneal cavity</p> Signup and view all the answers

    What characterizes the presence of early antral and pre-antral follicles in the ovaries?

    <p>They are continuously present between puberty and menopause</p> Signup and view all the answers

    Which cells are primarily responsible for secreting progesterone and estrogen in the corpus luteum?

    <p>Granulosa and theca cells</p> Signup and view all the answers

    What physiological change occurs in the endometrium due to a decrease in oestrogen and progesterone during the menstrual phase?

    <p>Degeneration and shedding of the stratum functionalis</p> Signup and view all the answers

    Which of the following hormones is primarily responsible for the thickening of cervical mucus during the menstrual cycle?

    <p>Progesterone</p> Signup and view all the answers

    What is indicated by a decrease in Anti Mullerian Hormone (AMH) levels?

    <p>Decreased follicle number</p> Signup and view all the answers

    During which phase of the menstrual cycle does the endometrium undergo gradual rebuilding?

    <p>Proliferative phase</p> Signup and view all the answers

    What is the primary functional change in the corpus luteum if pregnancy does not occur?

    <p>It degenerates and forms the corpus albicans</p> Signup and view all the answers

    What is the function of oestrogen during the ovarian cycle at low concentrations?

    <p>Causes negative feedback on FSH/LH</p> Signup and view all the answers

    Which event triggers ovulation in the menstrual cycle?

    <p>Surge of luteinizing hormone (LH)</p> Signup and view all the answers

    What changes occur in the endometrium due to high concentrations of progesterone?

    <p>Induces secretory transformation of the endometrium</p> Signup and view all the answers

    What is the primary fate of the corpus luteum if fertilization does not occur?

    <p>It degenerates and ceases hormone production</p> Signup and view all the answers

    During which phase of the menstrual cycle does the secretory endometrium form?

    <p>Luteal Phase</p> Signup and view all the answers

    Which hormone is primarily responsible for the proliferation of the endometrium during the menstrual cycle?

    <p>Oestrogen</p> Signup and view all the answers

    What effect does the degeneration of the corpus luteum have on menstrual cycle hormones?

    <p>Increases FSH and LH production</p> Signup and view all the answers

    What triggers the release of oestrogen during follicle growth?

    <p>Growth of more granulosa cells</p> Signup and view all the answers

    What physiological change occurs as a result of the LH surge during ovulation?

    <p>Completion of the first meiotic division of the primary oocyte</p> Signup and view all the answers

    Which hormone is responsible for providing negative feedback to LH and FSH during the luteal phase?

    <p>Inhibin</p> Signup and view all the answers

    What is the role of aromatase in the ovarian cycle?

    <p>Converts androgens to estrogens</p> Signup and view all the answers

    What effect does a decrease in FSH have on the follicles during the follicular phase?

    <p>Only the dominant follicle survives</p> Signup and view all the answers

    How does the corpus albicans affect the menstrual cycle when it forms?

    <p>Decreases plasma progesterone and estrogen levels</p> Signup and view all the answers

    What primarily stimulates the granulosa cells during the early stages of the follicular phase?

    <p>Follicle-stimulating hormone (FSH)</p> Signup and view all the answers

    During which phase of the ovarian cycle does inhibin primarily decrease FSH levels?

    <p>Luteal phase</p> Signup and view all the answers

    What effect does high plasma concentration of estrogen have on the anterior pituitary?

    <p>Stimulates an LH surge</p> Signup and view all the answers

    What initiates the anterior pituitary to secrete LH and FSH at the beginning of the menstrual cycle?

    <p>GnRH released by hypothalamus</p> Signup and view all the answers

    How does the degradation of the corpus luteum influence the menstrual cycle?

    <p>Leads to a decrease in progesterone and estrogen</p> Signup and view all the answers

    Study Notes

    Overview of Interactions between Female Cycles

    • Follicular growth leads to more granulosa cells which release increasing amounts of oestrogen.
    • Oestrogen causes proliferation of the endometrium and has a negative feedback on FSH and LH at low concentrations, but a positive feedback at high concentrations.
    • An LH surge triggers ovulation on day 14.
    • The leftover follicle becomes the Corpus Luteum, which releases progesterone and oestrogen, inducing a secretory endometrium.
    • If pregnancy does not occur, the Corpus Luteum degenerates.
    • This leads to a decrease in progesterone and oestrogen, causing menstruation and removing inhibition on FSH and LH, allowing for follicle growth again.

    Folliculogenesis

    • Folliculogenesis is the process of follicle growth, which can take over 6 months.
    • Early antral and pre-antral follicles are always present between puberty and menopause.
    • At the start of each menstrual cycle, 10-25 pre-antral and early antral follicles develop, but only one dominant follicle will continue to develop, influenced by local oestrogen levels.
    • The mature Graafian follicle contains a 1° oocyte that completes the first mitotic division resulting in a 2° oocyte.
    • The cumulus oophorus, connected by the corona radiata, separates and floats in the antral fluid.

    Ovulation

    • LH is the main initiator of ovulation.
    • The ballooning walls of the follicle and ovary rupture at the stigma, releasing the oocyte into the peritoneal cavity.

    Corpus Luteum

    • The Corpus Luteum is formed by luteal and thecal cells and a fibrous clot.
    • It secretes progesterone and oestrogen for 3 months if pregnancy occurs.
    • It degenerates after 10 days if no pregnancy occurs.

    Hormone Roles

    • Oestrogen: produced by granulosa cells, thins cervical mucus, promotes proliferative phase, and promotes progesterone receptor expression.
    • Progesterone: produced by the Corpus Luteum, thickens cervical mucus, inhibits prostaglandin-induced contractions, and lowers fallopian tube motility.

    Anti Mullerian Hormone (AMH)

    • This hormone indicates follicle number and ovarian reserve.
    • AMH levels decrease with age and infertility.

    Uterine/Menstrual Cycle

    • Cyclic changes in the uterine endometrium in response to ovarian steroid hormones.
    • Phases: Menstrual phase (D1-5), Proliferative phase (D6-14), Secretory phase (D15-28).
    • Endometrium: Stratum functionalis (functional) and Stratum basalis (unresponsive to ovarian hormones).

    Menstrual Phase (D1-5)

    • Shedding of stratum functionalis, losing approximately 30-40 ml of blood (sometimes up to 60 ml).
    • Decrease in oestrogen/progesterone leads to endometrial deprivation.
    • Increase in prostaglandin causes vasoconstriction of spiral arterioles and uterine contractions.
    • Ischemic endometrial cells die, and then spiral arterioles dilate, causing haemorrhaging through weakened capillary walls.
    • The stratum functionalis is sloughed off.

    Proliferative / Preovulatory Phase (D6-14)

    • Rebuilding of the stratum functionalis (2-8 mm).
    • Proliferation of glandular epithelial cells, stroma, and blood vessels with glandular enlargement.
    • Increase in plasma oestrogen due to dominant follicle development, promoting progesterone receptor expression and thinning cervical mucus for sperm passage.
    • Ovulation marks the end of this phase.

    Secretory / Postovulatory Phase (D15-28)

    • Prepares endometrium for implantation.
    • Glandular and stromal enlargement, and artery elongation.
    • Secretion of nutritious glycogen, mucopolysaccharides, and glycoproteins.
    • Progesterone and oestrogen drive this phase, with progesterone causing cervical mucus thickening and inhibiting uterine contractions.
    • If no fertilization, the Corpus Luteum degenerates.
    • Subsequently, progesterone production stops, leading to artery spasms, low oxygen levels, and menstruation.

    Ovarian Cycle

    • Series of changes in the ovary where a follicle matures, an ovum is shed, and a corpus luteum develops
    • Divided into two phases:
      • Follicular phase (Day 1-14): for follicle growth
      • Luteal phase (Day 15-28): for corpus luteum activity

    Folliculogenesis

    • Takes over six months for a primordial follicle to grow and mature into an ovulatory follicle
    • There are always early antral and pre-antral follicles in the ovaries between puberty and menopause

    Stages of Follicular Development

    • Primordial follicle:
      • Single layer of squamous stromal cells (pre-granulosa cells)
      • Present before birth
      • Some primordial follicles are recruited and activated each month between puberty and menopause to form primary follicles
    • Primary follicle:
      • Cuboidal granulosa cells
      • Formation of the zona pellucida
    • Mature/Graafian/3°/Preovulatory follicle:
      • 1° oocyte completes its first meiotic division, resulting in a 2° oocyte
      • Cumulus oophorus separates and floats in the antral fluid, connected by the corona radiata

    Ovulation

    • LH is the major initiator
    • Ballooning walls of the follicle and ovary rupture at the site where they are joined (stigma), expelling the ovum into the peritoneal cavity

    Corpus Luteum

    • Forms from luteal and thecal cells
    • Forms a fibrous clot
    • Secretes progesterone and estrogen (for three months if pregnancy occurs)
    • Degenerates within 10 days if pregnancy does not occur to form a corpus albicans

    Corpus Albicans

    • A mass of fibrous tissue
    • Gradually resorbed in the ovary

    Hormonal Control of the Ovarian Cycle

    • Controlled by GnRH pulses released by the hypothalamus
    • Ovarian hormones:
      • Estrogen peaks in the middle of the follicular and mid-luteal stage (Day 12 and Day 21)
      • Progesterone peaks on Day 21
    • Anterior pituitary hormones:
      • LH and FSH rise toward the end of the cycle
      • LH surge (Day 14) causes ovulation

    Hormonal Control of the Follicular Phase

    • GnRH released by the hypothalamus stimulates FSH and LH release by the anterior pituitary
    • LH:
      • Stimulates theca cells to produce androgens
    • FSH:
      • Supports the development of pre-antral and early antral follicles
      • Enlarges and multiplies granulosa cells
      • Converts androgens to estrogens via aromatase
    • Estrogen and inhibin (from granulosa cells):
      • Negatively feedback on LH and FSH
    • Only the dominant follicle survives the drop in FSH

    Hormonal Control of Ovulation

    • Follicle maturation causes the release of large amounts of estrogen
    • Estrogen has a positive feedback effect on the hypothalamic-pituitary axis
    • LH surge causes ovulation:
      • Stimulates the primary oocyte to complete the first meiotic division, forming a 2° oocyte
      • Increases the size of the antrum and blood flow
      • Granulosa cells release enzymes and prostaglandins that break down follicular and ovarian membranes
      • Granulosa cells produce more progesterone and decrease estrogen production
      • The ruptured follicle becomes the corpus luteum

    Hormonal Control of the Luteal Phase

    • Increased progesterone and estrogen released by the corpus luteum negatively feedback to LH and FSH
    • Release of inhibin decreases FSH
    • Declining gonadotropin (LH and FSH) levels prevent development of additional follicles and LH surges
    • The corpus luteum degrades within two weeks, resulting in decreased plasma progesterone and estrogen

    Hormonal Control of Cycles - Summary

    • Estrogen:
      • Low levels inhibit FSH and LH, high levels cause LH surge
      • Produced by the follicle (LH stimulates theca cells to produce androgens, FSH stimulates granulosa cells to produce estrogen) and corpus luteum
      • Thins cervical mucus
      • Induces the proliferative phase
      • Promotes progesterone receptor expression
    • Progesterone:
      • Produced by the corpus luteum
      • Thickens cervical mucus
      • Inhibits prostaglandins (causing relaxtion)
      • Low levels cause low fallopian tube motility
    • Anti Mullerian Hormone (AMH):
      • Indicates follicle number and ovarian reserve (product of growing follicles)
      • Declines with age and infertility

    Uterine/Menstrual Cycle

    • Series of cyclic changes in the uterine endometrium in response to rising and falling ovarian steroid hormones in the blood
    • Divided into three phases:
      • Menstrual phase (Day 1-5)
      • Proliferative phase (Day 6-14)
      • Secretory phase (Day 15-28)

    Endometrium

    • Part of the uterus that is shed during menstruation
    • Consists of two layers:
      • Stratum functionalis - functional layer
        • Columnar epithelium
        • Connective tissue stroma
        • Simple tubular uterine glands
        • Spiral arteries
      • Stratum basalis - unresponsive to ovarian hormones
        • Similar cell types to the stratum functionalis, but more compact

    Menstrual Phase (Day 1-5)

    • Shedding of the stratum functionalis of the endometrium
    • Average blood loss: 30-40 ml (up to 60 ml)
    • Process:
      1. Decreased estrogen and progesterone deprive the endometrium of hormonal support
      2. Increased prostaglandin production from the endometrium in response to decreased estrogen causes vasoconstriction of spiral arterioles and uterine contractions
      3. Endometrial cells become ischemic and die due to a decrease in oxygen and nutrients
      4. Spiral arterioles dilate, resulting in hemorrhage through weakened capillary walls

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