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Related Concept Videos

Oogenesis02:07

Oogenesis

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In human women, oogenesis produces one mature egg cell or ovum for every precursor cell that enters meiosis. This process differs in two unique ways from the equivalent procedure of spermatogenesis in males. First, meiotic divisions during oogenesis are asymmetric, meaning that a large oocyte (containing most of the cytoplasm) and minor polar body are produced as a result of meiosis I, and again following meiosis II. Since only oocytes will go on to form embryos if fertilized, this unequal...
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Oogenesis,  the process of developing egg cells (female gametes), occurs within the ovaries and is fundamental to female fertility. This sequence begins during fetal development when diploid oogonia in the developing ovaries undergo mitotic divisions to produce primary oocytes. By birth, these primary oocytes enter prophase I of meiosis but become arrested in this stage, remaining suspended until puberty.
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Folliculogenesis is the development of ovarian follicles, the specialized structures within the ovarian cortex where oogenesis, or egg development, occurs. This process is essential for female reproductive health and begins during fetal development when primordial follicles are formed. Each primordial follicle comprises a primary oocyte in the center, surrounded by a single layer of squamous pre-granulosa cells. These follicles remain dormant in late prophase I of meiosis until triggered by...
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The early endosome containing internalized molecules matures through transformations in its location, morphology, intraluminal pH, and membrane protein composition. Together, these changes result in a more acidic late endosome that contains multiple intraluminal vesicles; therefore, the late endosome is also called a multivesicular body (MVB).
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Cell division is necessary for growth and reproduction in organisms. Mitosis aids cell growth and development by dividing somatic cells. In contrast, meiosis causes the division of germ cells and plays an essential role in sexual reproduction. Due to their unique functional requirements, mitosis and meiosis differ from each other in multiple aspects.
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Meiosis II is the second and final stage of meiosis. It relies on the haploid cells produced during meiosis I, each of which contain only 23 chromosomes—one from each homologous initial pair. Importantly, each chromosome in these cells is composed of two joined copies, and when these cells enter meiosis II, the goal is to separate such sister chromatids using the same microtubule-based network employed in other division processes. The result of meiosis II is two haploid cells, each...
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Related Experiment Video

Updated: Nov 22, 2025

Human Egg Maturity Assessment and Its Clinical Application
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Human Egg Maturity Assessment and Its Clinical Application

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Cytoplasmic maturation in human oocytes: an ultrastructural study †.

Z Trebichalská1, D Kyjovská2, S Kloudová2

  • 1Department of Histology and Embryology, Faculty of Medicine, Masaryk University, Brno, Czech Republic.

Biology of Reproduction
|January 6, 2021
PubMed
Summary

Understanding human egg quality requires examining cytoplasmic maturation. This study reveals key ultrastructural changes in oocytes during maturation, offering insights into female fertility.

Keywords:
cytoplasmic maturationegg qualityelectron microscopyhuman oocytein vitro maturationoocyte ultrastructure

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Area of Science:

  • Reproductive Biology
  • Cell Biology
  • Developmental Biology

Background:

  • Female fertility depends on successful egg development, which involves cytoplasmic changes beyond chromosome segregation.
  • The morphological basis of cytoplasmic maturation in human oocytes is not well understood.
  • Oocyte quality is crucial for fertilization and embryonic development.

Purpose of the Study:

  • To investigate the ultrastructural changes in the cytoplasm of human oocytes during meiotic maturation in vitro.
  • To establish a morphological map of cytoplasmic maturation for reference in future studies.

Main Methods:

  • Ultrastructural analysis of 69 unfertilized human oocytes from healthy egg donors.
  • Comparison of oocytes at three consecutive developmental stages of in vitro maturation.
  • Morphometric image analysis to quantify cytoplasmic reorganization.

Main Results:

  • Significant cytoplasmic reorganization occurs before polar body extrusion, with organelles redistributing from the nucleus to the periphery.
  • Secretory apparatus transforms into cortical granules beneath the oocyte surface.
  • Heterologous complexes of endoplasmic reticulum and primitive mitochondria form during maturation.

Conclusions:

  • This study provides essential insights into the morphological changes during human oocyte cytoplasmic maturation.
  • The findings enhance understanding of intracellular factors influencing human egg quality.
  • A proposed morphological map serves as a reference for comparative studies on oocyte development.