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Questions and Answers
What role do theca interna cells play in estrogen synthesis?
What role do theca interna cells play in estrogen synthesis?
Which hormone is responsible for binding to granulosa cells to promote the conversion of androgens into estrogen?
Which hormone is responsible for binding to granulosa cells to promote the conversion of androgens into estrogen?
What is the function of the enzyme aromatase in the context of E2 synthesis?
What is the function of the enzyme aromatase in the context of E2 synthesis?
How do theca interna cells respond to Luteinizing Hormone (LH)?
How do theca interna cells respond to Luteinizing Hormone (LH)?
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What substance fills the antrum of the follicle during folliculogenesis?
What substance fills the antrum of the follicle during folliculogenesis?
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What is the dominant structure in the ovary during the luteal phase?
What is the dominant structure in the ovary during the luteal phase?
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Which hormone is primarily high during the follicular phase?
Which hormone is primarily high during the follicular phase?
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What occurs during the recruitment process of folliculogenesis?
What occurs during the recruitment process of folliculogenesis?
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Which phase of the estrous cycle is associated with the preovulatory surge of LH?
Which phase of the estrous cycle is associated with the preovulatory surge of LH?
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What is the classification maximum diameter of large antral follicles?
What is the classification maximum diameter of large antral follicles?
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What is the primary function of the tonic center in the hypothalamus during the estrous cycle?
What is the primary function of the tonic center in the hypothalamus during the estrous cycle?
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What does the surge center of the hypothalamus respond to in order to release a surge of GnRH?
What does the surge center of the hypothalamus respond to in order to release a surge of GnRH?
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What happens to most recruited follicles during folliculogenesis?
What happens to most recruited follicles during folliculogenesis?
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What is the main role of the corpus luteum after ovulation?
What is the main role of the corpus luteum after ovulation?
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Which hormone directly stimulates follicular recruitment?
Which hormone directly stimulates follicular recruitment?
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What is a key characteristic of the episodic profile of GnRH secretion from the tonic center?
What is a key characteristic of the episodic profile of GnRH secretion from the tonic center?
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Which stage of the estrous cycle does ovulation typically occur?
Which stage of the estrous cycle does ovulation typically occur?
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What happens during the dominance process in folliculogenesis?
What happens during the dominance process in folliculogenesis?
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What is primarily secreted by the corpus luteum during the luteal phase?
What is primarily secreted by the corpus luteum during the luteal phase?
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What hormone is primarily responsible for preventing high quantities of GnRH release during the luteal phase?
What hormone is primarily responsible for preventing high quantities of GnRH release during the luteal phase?
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Which phase of the reproductive cycle is characterized by the presence of a corpus luteum secreting progesterone?
Which phase of the reproductive cycle is characterized by the presence of a corpus luteum secreting progesterone?
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What effect does elevated estradiol (E2) have on GnRH neurons during the follicular phase?
What effect does elevated estradiol (E2) have on GnRH neurons during the follicular phase?
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Which gonadotropin is primarily responsible for stimulating the growth of dominant follicles?
Which gonadotropin is primarily responsible for stimulating the growth of dominant follicles?
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What is the main consequence of low estradiol (E2) levels during the luteal phase?
What is the main consequence of low estradiol (E2) levels during the luteal phase?
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What role does inhibin play in the regulation of FSH secretion?
What role does inhibin play in the regulation of FSH secretion?
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How does luteolysis affect GnRH and LH release?
How does luteolysis affect GnRH and LH release?
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Which cells are responsible for producing E2 in the antral follicles?
Which cells are responsible for producing E2 in the antral follicles?
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What happens to most recruited follicles due to insufficient FSH levels?
What happens to most recruited follicles due to insufficient FSH levels?
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What is the relationship between FSH and the early selection of follicles?
What is the relationship between FSH and the early selection of follicles?
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What hormone's secretion is negatively regulated by the combination of E2 and inhibin?
What hormone's secretion is negatively regulated by the combination of E2 and inhibin?
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During which phase is the preovulatory surge of GnRH primarily influenced by estradiol?
During which phase is the preovulatory surge of GnRH primarily influenced by estradiol?
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What is the outcome of a lack of progesterone after luteolysis on the GnRH pulse frequency?
What is the outcome of a lack of progesterone after luteolysis on the GnRH pulse frequency?
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Which follicular phase is marked by the absence of P4 secretion from the corpus luteum?
Which follicular phase is marked by the absence of P4 secretion from the corpus luteum?
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What triggers luteolysis during the estrous cycle?
What triggers luteolysis during the estrous cycle?
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What role does estrogen play in the release of PGF2α?
What role does estrogen play in the release of PGF2α?
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During which phase does LH stimulate final growth and maturation of follicles?
During which phase does LH stimulate final growth and maturation of follicles?
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How do rising levels of estrogen affect the secretion of gonadotropins?
How do rising levels of estrogen affect the secretion of gonadotropins?
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What is the primary consequence of high progesterone during the first follicular wave?
What is the primary consequence of high progesterone during the first follicular wave?
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Which event occurs after luteolysis has taken place?
Which event occurs after luteolysis has taken place?
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What effect does high progesterone have on GnRH secretion?
What effect does high progesterone have on GnRH secretion?
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What are the stages of the estrous cycle mentioned in the content?
What are the stages of the estrous cycle mentioned in the content?
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What signifies the emergence of the dominant follicle?
What signifies the emergence of the dominant follicle?
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What hormone primarily stimulates recruitment of small antral follicles?
What hormone primarily stimulates recruitment of small antral follicles?
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What occurs in the absence of progesterone during the follicular phase?
What occurs in the absence of progesterone during the follicular phase?
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How does inhibin influence FSH secretion?
How does inhibin influence FSH secretion?
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What initiates the recruitment of follicles in the folliculogenesis process?
What initiates the recruitment of follicles in the folliculogenesis process?
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What defines the process of follicular selection?
What defines the process of follicular selection?
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During which phase is the final follicular wave prior to ovulation observed?
During which phase is the final follicular wave prior to ovulation observed?
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Study Notes
Reproductive Cyclicity
- There are two phases of the estrous cycle (follicular and luteal)
- the follicular phase involves the development of antral follicles
- the luteal phase involves the development of the corpus luteum
- There are four stages of the estrous cycle:
- Proestrus - follicular phase
- Estrus - follicular phase
- Metestrus - luteal phase
- Diestrus - luteal phase
- The luteal phase is characterized by high levels of progesterone (P4) and a dominant corpus luteum
- The follicular phase is characterized by high levels of estradiol (E2) and a dominant antral follicle
- During ovulation, the dominant follicle ruptures and releases an oocyte
- After ovulation, the ruptured follicle becomes the corpus luteum
Folliculogenesis
- Folliculogenesis is the process of ovarian follicular growth and degeneration
- Antral follicles are classified based on their diameter:
- Small (1-5 mm)
- Medium (5.1-7.9 mm)
- Large (>8 mm)
- Follicular dynamics involves 4 processes:
- Recruitment: a cohort of small antral follicles start to grow and secrete E2
- Selection: follicles are selected to become dominant or undergo atresia
- Dominance: the preovulatory follicle(s) keeps growing
- Ovulation: the preovulatory follicle ruptures to release the oocyte
Folliculogenesis: Hormonal Regulation
- The hypothalamus releases gonadotropin-releasing hormone (GnRH)
- The tonic center is responsible for basal secretion of GnRH
- The surge center is responsible for the preovulatory secretion of GnRH
- The anterior pituitary releases follicle-stimulating hormone (FSH) and luteinizing hormone (LH)
- The ovary releases estradiol (E2) and inhibin
- The corpus luteum releases progesterone (P4)
- During the luteal phase:
- P4 levels are high, inhibiting the release of GnRH from the tonic and surge centers
- The combination of low P4 and low E2 reduces the degree of GnRH neurons firing in the surge center through negative feedback
- During the follicular phase:
- P4 levels are low, allowing high levels of GnRH to be released
- E2 stimulates firing by GnRH neurons in the surge center through positive feedback
- This positive feedback results in the preovulatory surge of LH
- LH promotes the final growth and maturation of dominant follicles and stimulates ovulation
- FSH stimulates the recruitment and secretion of E2 in early stage follicles
Folliculogenesis: Estrogen Synthesis
- E2 synthesis is regulated by FSH and LH
- E2 is produced in the antral follicles by the communication between theca interna cells and granulosa cells
Folliculogenesis
-
Estrogen (E2) synthesis in antral follicles:
- Theca interna cells produce androgens (e.g., testosterone) in response to luteinizing hormone (LH).
- Granulosa cells have follicle-stimulating hormone (FSH) receptors and convert androgens into E2 using the enzyme aromatase.
- Dominant follicles have both LH and FSH receptors for final maturation.
Luteolysis
- Luteolysis is the degeneration of the corpus luteum, which initiates the follicular phase of the estrous cycle.
- Progesterone (P4) secretion from the corpus luteum is stopped, leading to increased gonadotropin secretion by the anterior pituitary.
- Prostaglandin F2⍺ (PGF2⍺), released by the endometrium, induces luteolysis.
- Estrogen (E2) stimulates the release of PGF2⍺, but only after the endometrium has been exposed to P4 for a period of time (P4 priming).
Ovarian Folliculogenesis in Waves
- Occurs in waves, with multiple follicles recruited and selected at different stages.
- Follicles of the first wave usually become atretic (degenerate) due to high P4 levels.
- FSH stimulates recruitment, but is inhibited by E2 and inhibin from antral follicles.
- Rising E2 stimulates PGF2⍺ release, leading to luteolysis, and then a subsequent increase in FSH, LH, and E2 for the final follicular growth and ovulation.
Regulation of Folliculogenesis
- Small antral follicles are recruited in response to FSH and start secreting E2 and inhibin.
- High P4 levels inhibit the tonic and surge centers, resulting in low LH pulse frequency and low GnRH release.
- As follicles grow, E2 and inhibin levels increase, further inhibiting FSH release.
- A dominant follicle secretes enough E2 to stimulate PGF2⍺ release from the P4-primed endometrium.
- Luteolysis eliminates the negative feedback from P4, allowing E2 to stimulate the preovulatory GnRH surge and subsequently the LH surge.
- Rising E2 levels trigger estrus behavior.
- LH stimulates final follicular growth and ovulation.
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Description
This quiz covers the phases of the estrous cycle, including the follicular and luteal phases, and the process of folliculogenesis. Learn about the stages of the estrous cycle and the classification of antral follicles by size. Test your knowledge on ovarian follicular dynamics and hormonal changes.
