Animal Science 434

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Animal Science 434

• Lecture 10 The Follicular Phase of the Estrous
  Cycle

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Tonic and Preovulatory Surge of GnRH
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Hypothalamus
Progesterone
(-)
Estradiol
GnRH
(-)
Anterior Pituitary
Inhibin (-)
LH, FSH
Estradiol
LH, FSH
LH
CL
Follicle
Ovary
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Tonic and Preovulatory Surge of GnRH
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Follicular Phase
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Hypothalamus
GnRH
Anterior Pituitary
Inhibin (-)
LH, FSH
Estradiol
LH, FSH
Follicle
Ovary
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Hypothalamus
GnRH
Anterior Pituitary
Inhibin (-)
LH, FSH
Estradiol
LH, FSH
Follicle
Ovary
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Follicular Phase
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Follicular Progression
Primordial
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Growth and Atresia of Follicles
Atresia
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Fate of follicles and oocytes.
Total of follicles
At birth
100,000 12 months
75,000 4-6 years
21,000 Aged cow
2,500 Follicles grow to
tertiary characteristic and degenerate.
Maximum number of oocytes ovulated for a cow
17 cycles/year x 8 year 136 oocytes
ovulated/lifespan
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Fate of follicles and oocytes.
Total of follicles
At birth
100,000 12 months
75,000 4-6 years
21,000 Aged cow
2,500 Follicles grow to
tertiary characteristic and degenerate.
Maximum number of oocytes ovulated for a cow
17 cycles/year x 8 year 136 oocytes
ovulated/lifespan
100 Days of Gestation 2.9 million
Can increase with superovulation with FSH to
stimulate the rescue of follicles which would
have undergone atresia
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Initial Follicular Growth
Small AntralFollicle
50 - 60 days
Gonadotropin Independent
FSH
Recruitment
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Follicular Waves in Cattle
Atresia
Follicular Size
Ovulation
FSH Sensitive Pool
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16
21
Ovulation
Day After Ovulation
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Follicular Waves in Cattle
Atresia
Follicular Size
Ovulation
FSH Sensitive Pool
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16
21
Ovulation
Day After Ovulation
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Follicular Waves in Cattle
Progesterone
Follicular Size
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16
21
Ovulation
Day After Ovulation
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Follicular Waves in Cattle
Progesterone
Follicular Size
Atresia
Dominance
Selection
Recruitment
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16
21
Ovulation
Day After Ovulation
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Follicular Waves in Cattle
Progesterone
Follicular Size
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16
21
Ovulation
Day After Ovulation
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Follicular Waves in Cattle
Progesterone
Follicular Size
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16
21
Ovulation
Day After Ovulation
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Follicular Waves in Cattle
Progesterone
Follicular Size
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16
21
Ovulation
Day After Ovulation
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Two Follicular Waves
Progesterone
Dominance
Follicular Size
Atresia
Ovulation
Selection
Recruitment
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Ovulation
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Day After Ovulation
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Follicular Wave Emergence

• FSH always controls emergence
• Increase in FSH precedes emergence

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Species Variation in Follicular Waves

• Cattle - 2 or 3 / cycle
• Sheep - 4 or 5 / cycle
• Pigs - 1 / cycle
• Horses - 1 / cycle
• Human - 1 / cycle

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Gonadotropin Action Withinthe Follicle
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Antral Follicle
Theca Internal
Granulosa
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Ovulation
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Germinal Epithelium
Tunica Albuginea
Theca Externa
Theca Interna
Basement Membrane
Granulosa
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Blocking of these events in the follicle
prevents ovulation.

• protein synthesis
• steroid synthesis
• prostaglandin synthesis
• plasminogen activator synthesis

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Preovulatory LH Surge
Ovulation
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Cumulus Expansion
Hyaluronic Acid and Protein Production
Unexpanded
Expanded
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Cumulus and Oocyte Separation
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Preovulatory LH Surge
Ovulation
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Preovulatory LH Surge
Ovulation
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Preovulatory LH Surge
Ovulation
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Preovulatory LH Surge
Ovulation
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Types of Ovulators
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Spontaneous Ovulators
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Induced Ovulators
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Induced Ovulators
Nerve endings sensing copulation
Copulation
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Hypothalamus
Blood LH
GnRH
Time (hr)
Posterior Pit.
Stimulation
LH
Anterior Pit.
Spinal Chord
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LH
Nerve endings sensing copulation
Copulation
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Cats

• Induced Ovulators
• Single copulation
• Only works 50 of the time
• Multiple copulations
• Higher LH surge

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Spontaneous Ovulators

• Retain some neural control of ovulation
• heifers can alter the timing of the LH surge by
  clitoral stimulation
• human rape cases result in higher than expected
  pregnancy rates

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Oogenesis
Primordial Germ Cells
Oogonia
Primary

Oocyte
Growth
Gonadotropin Independent
Gonadotropin Dependent
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Primordial Follicles in Fetal Pig Ovary
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Oogonia
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Primary Oocytes in Primordial Follicles
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Oogonia and Primary Oocytes
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Primary Oocyte in Primary Follicle
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Fetal Oocyte Development
Mitosis
Meiosis
Fertilization
Birth
Cow
280 d
Sow
114 d
Mouse
19 d
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Ovulation of Tertiary Follicle
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Formation of the Zona Pellucida
Corona Radiata
Oocyte
Zona Pellucida
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Corona Radiata
Zona Pellucida
Oocyte
Gap Junctions
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During Oocyte Growth and Before the LH Surge

• OMI - Oocyte Maturation Inhibitor
• MPF - Maturation promoting factor
• GV - germinal vesicle (nucleus)

cAMP
GV
pre-MPF
MPF
Gap Junctions Allow Cell to Cell Communication!
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The LH Surge
Gap Junctions are Destroyed!
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The LH Surge
Resumption of Meiosis
GVBD
GV
pre-MPF
MPF
Gap Junctions are Destroyed!
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First polar body
emitted, arrest at
Resumption of

LH Surge
metaphase II of meiosis
Meiosis
Primary Oocyte
Secondary
Oocyte
Ovulation
(most species)
Zygote (pronucleate egg)
Sperm
Penetration
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First polar body
emitted, arrest at
Resumption of

LH Surge
metaphase II of meiosis
Meiosis
Primary Oocyte
Secondary
Oocyte
Ovulation
(most species)
Zygote (pronucleate egg)
Sperm
Penetration