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Related Concept Videos

Oogenesis02:07

Oogenesis

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...
Oogenesis01:22

Oogenesis

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.
Each primary oocyte is surrounded by a layer of pre-granulosa cells, forming what is known...
Hormonal Regulation of the Menstrual Cycle01:22

Hormonal Regulation of the Menstrual Cycle

The ovarian cycle regulates endometrial changes throughout a single menstrual cycle via the coordinated action of gonadotrophin-releasing hormone (GnRH) and gonadotrophins.
At puberty, GnRH begins a pulsatile release pattern, which triggers the anterior pituitary gland to secrete follicle-stimulating hormone (FSH) and luteinizing hormone (LH). The frequency and amplitude of GnRH pulses vary across the menstrual cycle, with faster pulses favoring LH release and slower pulses favoring FSH release.
Hormonal Control of the Ovarian Cycle01:30

Hormonal Control of the Ovarian Cycle

The ovarian cycle is meticulously regulated by the hypothalamic-pituitary-gonadal axis. This cycle orchestrates the release of a mature oocyte, essential for reproduction.
Before puberty, the hypothalamus releases GnRH in a low frequency, low amplitude pulsatile manner. This along with the immature hypothalamic-pituitary-gonadal axis activity, results in low estrogen levels and the absence of a fully functional ovarian cycle.  At puberty, GnRH secretion increases in both frequency and...
Ovarian Cycle01:27

Ovarian Cycle

The menstrual cycle includes a critical component known as the ovarian cycle, which undergoes two main phases each month—the follicular phase and the luteal phase. The follicular phase is variable and averaging around 14 days. Ovulation, triggered by a surge in luteinizing hormone (LH), marks the transition between the two phases. The second phase, the luteal phase, is relatively consistent, lasting approximately 14 days, and is marked by the activity of the corpus luteum. While a cycle length...
Menopause01:28

Menopause

Menopause, a natural biological process marking the end of a woman's fertility, typically occurs between the fifth and sixth decade of life. This phase is characterized by the exhaustion of the ovarian follicle pool, leading to less responsive ovaries despite the high levels of Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH). The consequential decrease in estrogen production results in symptoms like hot flashes, heavy sweating, headaches, hair loss, muscle pains, vaginal...

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Related Experiment Video

Updated: Jul 8, 2026

Probing the Limits of Egg Recognition Using Egg Rejection Experiments Along Phenotypic Gradients
07:34

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Published on: August 22, 2018

Hematological changes associated with egg production: estrogen dependence and repeatability.

Emily C Wagner1, Jaime S Prevolsek, Katherine E Wynne-Edwards

  • 1Women's Health Research Institute, E204-4500 Oak Street, Box 42, Vancouver, British Columbia, V6H 3N1, Canada. ewagner3@cw.bc.ca

The Journal of Experimental Biology
|January 22, 2008
PubMed
Summary

Reproduction incurs costs, potentially linked to hormones. In female zebra finches, estrogen receptor blockade prevented the drop in hematocrit during egg-laying, suggesting a hormonal mechanism for reproductive costs.

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Area of Science:

  • Life history theory
  • Reproductive physiology
  • Avian biology

Background:

  • The cost of reproduction, a trade-off between current reproduction and future fitness, is central to life history theory.
  • Physiological mechanisms underlying reproductive costs are poorly understood.
  • Estrogen's role in reproduction may impose costs, such as reduced hematocrit during egg production.

Purpose of the Study:

  • To investigate the physiological mechanisms of reproductive costs.
  • To determine if estrogen's action on hematocrit during egg production is receptor-mediated.
  • To explore the repeatability of hematological changes and their relation to pre-breeding hematocrit.

Main Methods:

  • Experimental manipulation using the anti-estrogen tamoxifen in female zebra finches.
  • Measurement of hematocrit levels before and during egg production.
  • Analysis of repeatability of hematocrit and its decrease during egg production.

Main Results:

  • Blocking estrogen receptors with tamoxifen prevented the decrease in hematocrit during egg production.
  • Pre-breeding hematocrit and the magnitude of its decrease during egg production were repeatable.
  • Females with higher pre-breeding hematocrit showed larger decreases during egg production.

Conclusions:

  • The reduction in hematocrit during egg production is mediated by estrogen receptor action.
  • Hematological changes represent a potential mechanism for regulatory-network based trade-offs involving estrogen's pleiotropic effects.
  • Estrogen's essential reproductive functions may come at the cost of reduced oxygen-carrying capacity.