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Animal Science 434. Lecture 11: The Follicular Phase of the Estrous Cycle. Tonic and Preovulatory Surge of GnRH. Hypothalamus. Progesterone. (-). Estradiol. GnRH. (-). Anterior Pituitary. Inhibin (-). LH, FSH. Estradiol. LH, FSH. LH. CL. Follicle. Ovary.
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Animal Science 434 Lecture 11: The Follicular Phase of the Estrous Cycle
Hypothalamus Progesterone (-) Estradiol GnRH (-) Anterior Pituitary Inhibin (-) LH, FSH Estradiol LH, FSH LH CL Follicle Ovary
Progesterone (-) Estradiol (-) LH CL Hypothalamus GnRH Anterior Pituitary Inhibin (-) LH, FSH Estradiol LH, FSH Follicle Ovary
(+) Estradiol Hypothalamus GnRH Anterior Pituitary Inhibin (-) LH, FSH Estradiol LH, FSH Follicle Ovary
Primary Secondary Tertiary Follicular Progression Primordial
Growth and Atresia of Follicles Atresia
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 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
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 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.
Initial Follicular Growth Small AntralFollicle 50 - 60 days Gonadotropin Independent FSH Recruitment
Recruitment Dominance Selection Follicular Waves in Cattle Atresia Follicular Size Ovulation FSH Sensitive Pool 9 16 21 Ovulation Day After Ovulation
Progesterone Recruitment Dominance Selection Follicular Waves in Cattle Atresia Follicular Size Ovulation FSH Sensitive Pool 9 16 21 Ovulation Day After Ovulation
estradiolinhibin Atresia FSH estradiol (-) inhibin (-) Dominance Selection FSH estradiol (-) inhibin (-) Recruitment FSH estradiol (-) Follicular Waves in Cattle Progesterone FSH Follicular Size 9 16 21 Ovulation Day After Ovulation
Follicular Waves in Cattle Progesterone Follicular Size Atresia Dominance Selection Recruitment 9 16 21 Ovulation Day After Ovulation
Follicular Waves in Cattle Progesterone Follicular Size 9 16 21 Ovulation Day After Ovulation
Follicular Waves in Cattle Progesterone Follicular Size 9 16 21 Ovulation Day After Ovulation
Ovulation Dominance Selection Recruitment Follicular Waves in Cattle Progesterone Follicular Size 9 16 21 Ovulation Day After Ovulation
Two Follicular Waves Progesterone Dominance Follicular Size Atresia Ovulation Selection Recruitment Ovulation 10 21 Day After Ovulation
Follicular Wave Emergence • Recruitment = Emergence • FSH always controls emergence • Increase in FSH precedes emergence
Cl-progesterone Cl-progesterone, inhibin Species Variation in Follicular Waves • Cattle - 2 or 3 / cycle • Sheep - 4 or 5 / cycle • Pigs - 1 / cycle • Horses - 1 / cycle • Human - 1 / cycle
Antral Follicle Theca Internal Granulosa
Theca Interna LH Receptor cAMP Cholesterol PKA Testosterone FSH Receptor Blood cAMP Testosterone PKA Estradiol Granulosa
Theca Interna Selection LH LH Receptor Receptor Dominant Follicle Express LH Receptor cAMP Cholesterol PKA Testosterone FSH Receptor Blood cAMP cAMP Testosterone PKA Estradiol Granulosa
Germinal Epithelium Tunica Albuginea Theca Externa Theca Interna Basement Membrane Granulosa
Blocking of these events in the follicle prevents ovulation. • protein synthesis • steroid synthesis • prostaglandin synthesis • plasminogen activator synthesis
Cumulus Expansion Oocyte Separates From Follicular Wall Preovulatory LH Surge Ovulation
Cumulus Expansion Hyaluronic Acid and Protein Production Unexpanded Expanded
Cumulus and Oocyte Separation
Cumulus Expansion Protein synthesis changes in and around Follicle Progesterone Plasminogen Activator Prostaglandin Synthesis PGE and PGF Oocyte Separates From Follicular Wall Preovulatory LH Surge Ovulation
Cumulus Expansion Increased Blood Flow to Ovary and Follicle Protein synthesis changes in and around Follicle Vascular Permeability Progesterone Plasminogen Activator Prostaglandin Synthesis PGE and PGF Plasminogen Oocyte Separates From Follicular Wall Histamine PGE2 Preovulatory LH Surge Edema Follicularpressure Ovulation
Cumulus Expansion Increased Blood Flow to Ovary and Follicle Protein synthesis changes in and around Follicle Vascular Permeability Progesterone Plasminogen Activator Prostaglandin Synthesis PGE and PGF Collagenase (inactive) Plasminogen Plasmin Oocyte Separates From Follicular Wall Collagenase (active) Follicular Wall Weakens Histamine PGE2 Preovulatory LH Surge Edema Follicularpressure Ovulation
Cumulus Expansion Increased Blood Flow to Ovary and Follicle Protein synthesis changes in and around Follicle Vascular Permeability Progesterone Plasminogen Activator Prostaglandin Synthesis PGE and PGF Collagenase (inactive) Plasminogen Plasmin Oocyte Separates From Follicular Wall Collagenase (active) Contraction of Smooth Muscle Follicular Wall Weakens Histamine PGE2 Preovulatory LH Surge Edema Follicularpressure Ovulation
Sensory Neurons Penis Induced Ovulators Nerve endings sensing copulation Copulation
Hypothalamus Blood LH Time (hr) GnRH Posterior Pit. Stimulation LH Anterior Pit. Spinal Chord
Sensory Neurons Penis LH Nerve endings sensing copulation Copulation
Cats • Induced Ovulators • Single copulation • Only works 50% of the time • Multiple copulations • Higher LH surge
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
Migration to germinal ridge Mitotic divisions Follicle Cells Initiation of Meiosis Interphase DNA synthesis Meiotic prophase begins Prophase of Meiosis leptotene zygotene pachytene diplotene dictyotene Meiotic Arrest zona pellucida formation mRNA production protein synthesis cortical granule formation nuclear maturation cytoplasmic maturation Oogenesis Primordial Germ Cells Oogonia Primary Oocyte Growth Gonadotropin Independent Gonadotropin Dependent
Oogonia in Egg Nest Fetal Pig Ovary