Topic 91 - Hormonal changes during the estrus cycle Flashcards

1
Q

Words to inculde

A
  • Ovulation
    • E2 level high
    • GnRH → LH peak → ovulation
  • LH peak
    • Induces ovulation
    • Luteinization process
  • Corpus haemorragicum, luteinization
    • E2 and FSH level ↓
    • Luteninization due to previous LH peak
    • PRL level ↑
  • Early phase of corpus luteum
    • P4 level ↑
  • Flourishing corpus luteum
    • P$ level ↑

Luteal phase

  • Growing phase of corpus luteum
  • P4 level ↑
    • Due to ovulation and luteinization (ø ca)
  • PRL level ↑
  • Flourishing corpus luteum
    • Plasma E2 low
      • Due to negative effect of high P4 on CNS

Luteolysis (end of luteal phase)

  • PGF production in uterus → lysis of corpus luteum → plasma P4 ↓
  • PGF
    • Endometrium → ovary
      • Ru: v. endometrial → a. ovarica
      • Eq: systemic circulation

Follicular phase

  • FSH level ↑
    • Induces next ovarian cycle
  • Inhibin produced
  • High level of E2 and FSH → GnRH peak

Hypothalamus - pituitary - gonad axis

  • GnRH secretion
    • Tonic releasing center
      • Ventromedial hypothalamic nucleus (location)
      • Base levels of GnRH
      • Normal E2 and P4 plasma concentration
      • Negative feedback
    • Pulsatile releasing surge center
      • Preoptic area (location)
      • Positive feedback

Estrogen

  • The relevance of preovulatory estrogen peak
    • Pre-ovulatory E2 levels ↑ → GnRH peak & LH peak → ovulation
    • Negative-positive feedback change of the hypothalamic GnRH cells
  • Role of elevated E2 levels
    • Positive / negative feedback
    • Diestrus, metestrus: low E2 level
    • Proestrus: elevated E2 level
      • Negative feedback → positive feedback → GnRH peak / surge
      • Gonadotropic cells ↑
        • Adenohypophysis
        • GnRH ↑ → LH peak

Luteinizing hormone (LH)

  • Peptide hormone
  • Secretion regulation:
    • GnRH
    • Sexual steroids
      • Positive: E2
      • Negative: P4
  • Role:
    • Surge center → GnRH ↑ → LH peak → ovulation, luteinization
    • Induced ovulators: Copulation → neuroendocrine reflex arch → LH peak → ovulation, luteinization
  • Supports theca cells
    • Provides androgens & hormonal precursors for estradiol production
    • FSH intiates follicular growth affecting granulosa cells
    • E2 level ↑ → LH receptors expressed on maturing follicle → estradiol production ↑
  • LH peak / surge
    • Trigger ovulation
    • Residual follicle → corpus luteum
      • P4 production to prepare endometrium

Refractory period of corpus luteum

  • PGF
    • No effect on corpus luteum for 2-5 days after ovulation

Regulation of seasonality

  • ​Length of diurnal periods (stimulator)
    • “Rushing into cycle”
  • Melatonin concentrations
  • Fall:
    • Length of dark period > 9.5 hours
    • Sheep: cycle starts
    • Eq: cycle inhibited
  • Spring:
    • Length of dark period < 9.5 hours
    • Sheep: cycle inhibited
    • Eq: cycle starts
  • Sheep: estrus cycle in short-day periods
  • Eq: estrus cycle in long-day periods
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2
Q

Topics to include in the essay

A
  1. Review of hormonal events
  2. Secretion of Gnrh
  3. Hypothalamus-hypohphysis-gonad axis
  4. Estrogen
    • The relevance of preovulatory E2 peak
    • Role of elevated E2 levels (+ /- feedback)
  5. Luteinizing hormone (LH)
  6. Refractory period of corpus luteum
  7. Regulation of seasonality
    • Horse and sheep
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3
Q

Figure: a review of hormonal events in cow

A
  • Chagens of plasma hormone leves during estrus cycle
  • Ovulation (18-0)
    • High level of E2
    • GnRH then LH peakovulation
      • ​LH peak incues the ovulation and luteinization process
    • High level of H2
  • Corpus haemorragicum, luteinization (0-5)
    • Dropping level of E2 and FSH
    • Due to previous LH-peak, luteinization is in progress
    • PRL levels ↑
  • Early phase of corpus luteum (5)
    • P4 levels ↑
    • A new generation of follicular cohort starts developing, but increasing P4 levels stops the process
  • Flourishirng corpus luteum (10-15)
    • High level of P4
    • Other hormones are on a baseline concentration
    • A new generation of follicles starts beveloping, but these follicles soon udergo the stresia
  • Luteolysis, early follicular development (15-18)
    • Non-pregnant animals
    • PGF is produced by the uterus → lysis of corpus luteum
    • P4 level ↓ → FSH level ↑
  • Follicular development and selection (17-21)
    • Increasing FSH levels stimulate the follicular development
    • Inhibis is produced by the fastest developing follicle (dominant follicle)
      • Inhibin blocks the other developing follicles
      • Some species: Inhibin cause a sharp drop in plasma FSH levels (negative feedback)
    • Due to constant high level of E2 and FSH, GnRH peak (followed by LH peak) develops and consequently next ovulation happens
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4
Q

Secretion of GnRH

A
  • GnRH: Gonadotropin Releasing Hormone
  • GnRH frequency is influenced by:
    • Estrous phase (hormones)
    • Season (melatonin)
    • Energy balance
  • Integration:
    • ​Kisspeptin-containing neurons
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5
Q

Hypothalamus-hypophysis-gonad axis

A
  • Feedback mechanism
  • Two aspects of GnRH secretion:
    • Tonic releasing center
      • Location: ventromedial hypothalamic nuclei
      • Ensures base levels of GnRH secretion necessary for functioning of the gonads
      • Normal E2 and P4 plasam concentration
      • Negative feedback loop
    • Pulsatile releasing surge center
      • Location: preoptic area
      • Produces a peak above the base level in every cycle
      • This center is stimulated by the high level of E2, a positive feedback loop
      • P4 in high concentration inhibits this center
      • The cyclic center affects functioning of the toic center
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6
Q

Estrogen

A
  • Estrogen = E2

The relevance of preovulatory estrogen peak

  • Rising pre-ovulatory estrogen levels directly prepare the GnRH peak and LH peak and therefore the ovulation
    • ​Pre-ovulatory estrogen level → GnRH peak and LH peak → ovulation
    • Negative-positive feedback change of the hypothalamic GnRH cells

Role of elevated E2 levels (+/- feedback)

  • E2 levels shows strong fluctation:
    • Diestrus, metestrus: low level
      • Inhibits the central GnRH secretion that keeps the noral baseling level of GnRH and LH in the circulation
    • Proestrus: elevates rapidly
      • Constant high level of E2 changes the feedback state of the GnRH cell from negative feedback to positive feedback → GnRH peak
      • Sensitivity of gonadotropic cells (FSH, LH) in the adenohypophysis icreases, and the elevated GnRH induces LH peak
      • LH peak → ovulation of fully matured follicle
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7
Q

Luteinizing hormone (LH)

A
  • Peptide hormone
  • Secretion regulated by:
    • GnRH
    • Sexual steroids
      • Positive: E2
      • Negative: P4
  • Role:
    • Surge center → GnRH ↑ → LH peak → ovulation, luteinization
    • Induced ovulators: Copulation → neuroendocrine reflex arch → LH peak → ovulation, luteinization
  • LH supports theca cells in the ovaries that provides androgens and hormonal precursors for estradiol production
    • FSH initiates follicular growth affecting granulosa cells → E2 increase → LH receptors expressed on the maturing follicle → estradiol production ↑
  • GnRH in the hypothalamus stimulates the release of LH from the anterior pituitary → LH peak
  • LH surge / LH peak triggers ovulation resulting in:
    • Releasing egg from follicle
    • Initiating the conversion of the residual follicle → corpus luteum whic produces P4 for preparation of endometrium for possible implantation
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8
Q

Refractory period of corpus luteum

A
  • PGFhas no effect on the corpus luteum for 2-5 days after ovulation

Refractory period of corpus luteum, interspecies

  • Ru: 4 days
  • Sus: 5 days
  • Eq: 13 days
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9
Q

Regulation of seasonality

A
  • The most important stimulator in seasonality is the length of diurnal periods, that determines the “rushing into cycle” process
  • Major role: Melatonin concentrations
  • During fall:
    • Length of dark period ↑, becomes more than 9.5 hours
    • The “rushing into cycle” starts for those which are sensitive for short day
      • Sheep: activated cycle
      • Eq: inhibited cycle
  • During spring:
    • Length of the dark periods ↓, becomes less than 9.5 hours
    • Cycle starts for those which are sensitive for long day light
      • Sheep: inhibited cycle
      • Eq: activated cycle
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