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Questions and Answers
What is the outcome of the maturation process of oogonia after they differentiate into primary oocytes?
At what stage do primary oocytes become surrounded by a layer of flat epithelial cells?
Which event marks the beginning of cell death in oogonia and primary oocytes?
What characterizes the diplotene stage that primary oocytes enter before birth?
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What primarily happens to the majority of oogonia by the seventh month of development?
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What initiates the development of primordial follicles?
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What is the maximum number of germ cells reached during the development of oocytes?
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Why do primary oocytes not complete their first meiotic division before puberty?
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What is the role of oocyte maturation inhibitor (OMI)?
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Which layer develops as granulosa cells proliferate and form a stratified epithelium?
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How many primary oocytes are typically present at the onset of puberty?
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What is the longest stage in the maturation of follicles?
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What results from the coalescence of fluid-filled spaces between granulosa cells?
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What cellular change occurs in surrounding follicular cells as primordial follicles begin to grow?
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What is the purpose of the finger-like processes extending from follicular cells?
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During which phase does the follicle become known as a mature vesicular follicle or Graafian follicle?
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What structure forms from the granulosa cells surrounding the oocyte at maturity?
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What triggers the preovulatory growth phase in the secondary follicle?
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What happens to the first polar body after meiosis I is completed?
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Which of the following statements about meiosis II is correct?
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What is the ploidy of the secondary oocyte?
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Which of the following structures merges with the ovarian connective tissue?
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What occurs to most follicles during the ovarian cycle?
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What is the main function of the theca interna cells?
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Study Notes
Oogenesis Overview
- Oogenesis is the process where oogonia develop into mature oocytes.
- Begins with primordial germ cells (PGCs) differentiating into oogonia in the female gonad.
Development Stages
- At 3 months of gestation, oogonia are in clusters, surrounded by flat epithelial follicular cells.
- Majority of oogonia continue mitosis; some enter meiosis and form primary oocytes.
- Maximum germ cell count reaches about 7 million by the 5th month.
- Cell death leads to degeneration, with most oogonia and primary oocytes becoming atretic by 7 months gestation.
Primary Oocyte Characteristics
- Surviving primary oocytes arrest in prophase of meiosis I, forming primordial follicles.
- The arrested state is maintained by oocyte maturation inhibitor (OMI) produced by follicular cells.
- Total primary oocytes at birth estimated between 600,000 to 800,000, reducing to approximately 40,000 by puberty.
Maturation at Puberty
- At puberty, 15 to 20 primordial follicles begin maturing monthly.
- Follicular cells transition from flat to cuboidal, forming primary follicles with stratified granulosa cells.
- Granulosa cells create the zona pellucida around oocytes; theca folliculi develops into internal and external layers.
Follicle Development Stages
- Maturation progresses through three stages:
- Primary or preantral
- Secondary or antral (vesicular)
- Preovulatory (Graafian follicle)
- The antral stage accumulates fluid, with mature vesicular follicles reaching 25 mm or more in diameter before ovulation.
Luteinizing Hormone Surge
- A surge in luteinizing hormone (LH) initiates the preovulatory growth phase.
- Meiosis I completes, creating unequal daughter cells; one becomes the secondary oocyte while the other is the first polar body.
Secondary Oocyte Arrest
- The secondary oocyte enters meiosis II but is arrested in metaphase approximately 3 hours before ovulation.
- Completion of meiosis II occurs only if fertilization takes place, with degeneration of the oocyte if not fertilized within 24 hours post-ovulation.
Fertilization Process
- Secondary oocyte is released surrounded by follicle cells (nurse cells).
- Sperm enzymes, released from the acrosome, penetrate the zona pellucida to reach the egg cytoplasm for fertilization.
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Description
Test your knowledge on the process of oogenesis, including primary oocyte development and meiosis stages. This quiz covers key concepts and terminology necessary for understanding female gametogenesis.
