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Lecture 11: The Follicular Phase of the Estrous Cycle
Animal Science 434 Lecture 11: 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 LH Progesterone (-) CL Estradiol (-) GnRH Anterior Pituitary Inhibin (-) LH, FSH Estradiol LH, FSH Follicle Ovary
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Hypothalamus Estradiol (+) GnRH Anterior Pituitary Inhibin (-) LH, FSH Estradiol LH, FSH Follicle Ovary
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Follicular Phase
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Follicular Progression
Secondary Primary Primordial Tertiary
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Growth and Atresia of Follicles
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Fate of follicles and oocytes
Total # of follicles At birth ,000 12 months ,000 4-6 years ,000 Aged cow ,500 Follicles undergo atresia at all stages of development. 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 ,000 12 months ,000 4-6 years ,000 Aged cow ,500 Follicles undergo atresia at all stages of development. 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 Superovulation; rescue follicles from undergoing atresia with FSH treatment.
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Initial Follicular Growth
Small Antral Follicle days Gonadotropin Independent FSH Recruitment
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Follicular Waves in Cattle
Atresia Follicular Size Recruitment Dominance Ovulation Selection FSH Sensitive Pool Ovulation 9 16 21 Day After Ovulation
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Follicular Waves in Cattle
Progesterone Atresia Follicular Size Recruitment Dominance Ovulation Selection FSH Sensitive Pool Ovulation 9 16 21 Day After Ovulation
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Follicular Waves in Cattle
Progesterone Atresia estradiol inhibin FSH Follicular Size Dominance FSH estradiol (-) inhibin (-) Selection FSH estradiol (-) inhibin (-) Recruitment FSH estradiol (-) Ovulation 9 16 21 Day After Ovulation
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Follicular Waves in Cattle
Progesterone Follicular Size Atresia Dominance Selection Recruitment Ovulation 9 16 21 Day After Ovulation
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Follicular Waves in Cattle
Progesterone Follicular Size Ovulation 9 16 21 Day After Ovulation
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Follicular Waves in Cattle
Progesterone Follicular Size Ovulation 9 16 21 Day After Ovulation
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Follicular Waves in Cattle
Progesterone Dominance Recruitment Selection Ovulation Follicular Size Ovulation 9 16 21 Day After Ovulation
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Two Follicular Waves Follicular Size Day After Ovulation Progesterone
Dominance Follicular Size Atresia Ovulation Selection Recruitment Ovulation 10 21 Day After Ovulation
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Follicular Wave Emergence
Recruitment = 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 Cl-progesterone Cl-progesterone, inhibin
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Gonadotropin Action Within the Follicle
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Antral Follicle Theca Internal Granulosa
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Theca Interna Granulosa LH Receptor cAMP Cholesterol PKA Testosterone
Blood Receptor LH cAMP Cholesterol Testosterone PKA Testosterone Receptor FSH cAMP Estradiol PKA
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Theca Interna Selection Granulosa LH Receptor Dominant Follicle cAMP
Blood Receptor LH cAMP Receptor LH Selection Dominant Follicle Express LH Receptor cAMP Cholesterol Testosterone PKA Testosterone Receptor FSH cAMP Estradiol PKA
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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 Cumulus Expansion Oocyte Separates
From Follicular Wall Ovulation
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Cumulus Expansion Hyaluronic Acid and Protein Production Unexpanded
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Cumulus and Oocyte Separation
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Protein synthesis changes Prostaglandin Synthesis
Preovulatory LH Surge Cumulus Expansion Oocyte Separates From Follicular Wall Protein synthesis changes in and around Follicle Plasminogen Activator Progesterone Prostaglandin Synthesis PGE and PGF Ovulation
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Preovulatory LH Surge Ovulation Cumulus Increased Blood Expansion
Histamine PGE2 Preovulatory LH Surge Increased Blood Flow to Ovary and Follicle Vascular Permeability Plasminogen Cumulus Expansion Oocyte Separates From Follicular Wall Protein synthesis changes in and around Follicle Plasminogen Activator Progesterone Prostaglandin Synthesis PGE and PGF Edema Follicular pressure Ovulation
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Preovulatory LH Surge Ovulation Cumulus Increased Blood Expansion
Histamine PGE2 Preovulatory LH Surge Increased Blood Flow to Ovary and Follicle Vascular Permeability Plasminogen Cumulus Expansion Oocyte Separates From Follicular Wall Protein synthesis changes in and around Follicle Plasminogen Activator Progesterone Prostaglandin Synthesis PGE and PGF Collagenase (inactive) Follicular Wall Weakens Plasmin Collagenase (active) Edema Follicular pressure Ovulation
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Preovulatory LH Surge Ovulation Cumulus Increased Blood Expansion
Histamine PGE2 Preovulatory LH Surge Increased Blood Flow to Ovary and Follicle Vascular Permeability Plasminogen Cumulus Expansion Oocyte Separates From Follicular Wall Protein synthesis changes in and around Follicle Plasminogen Activator Progesterone Prostaglandin Synthesis PGE and PGF Collagenase (inactive) Follicular Wall Weakens Plasmin Collagenase (active) Contraction of Smooth Muscle Edema Follicular pressure Ovulation
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Types of Ovulators
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Spontaneous Ovulators
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Induced Ovulators
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Nerve endings sensing copulation
Induced Ovulators Nerve endings sensing copulation Sensory Neurons Penis Copulation
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Hypothalamus Blood LH Time (hr) GnRH Posterior Pit. Stimulation LH Anterior Pit. Spinal Chord
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Nerve endings sensing copulation
LH Nerve endings sensing copulation Sensory Neurons Penis 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 Gonadotropin Independent Gonadotropin Dependent
Migration to germinal ridge Mitotic divisions Primordial Germ Cells Oogonia Follicle Cells Initiation of Meiosis Interphase DNA synthesis Meiotic prophase begins Prophase of Meiosis leptotene zygotene pachytene diplotene Meiotic Arrest dictyotene Primary Oocyte Growth Gonadotropin Independent zona pellucida formation mRNA production protein synthesis cortical granule formation Gonadotropin Dependent nuclear maturation cytoplasmic maturation
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Oogonia in Egg Nest Fetal Pig Ovary
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Oogonia and Primary Oocytes
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Primary Oocytes in Primordial Follicles
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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 OMI cAMP PKA 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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Gap Junctions are Destroyed!
The LH Surge cAMP Resumption of Meiosis GVBD PKA GV pre-MPF MPF Gap Junctions are Destroyed!
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2N 4N (most species) N First polar body Resumption of
emitted, arrest at LH Surge Meiosis metaphase II of meiosis 4N 2N N Primary Oocyte Secondary Oocyte Ovulation (most species) Zygote (pronucleate egg) Sperm Penetration
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2N 4N Sperm Penetration Ovulation Dog Fox (most species) N
First polar body Resumption of emitted, arrest at LH Surge Meiosis metaphase II of meiosis 4N 2N N Ovulation Dog Fox Sperm Penetration Primary Oocyte Secondary Oocyte Ovulation (most species) Zygote (pronucleate egg) Sperm Penetration
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