Animal Science 434 Lecture 10: The Follicular Phase of the Estrous Cycle
Tonic and Preovulatory Surge of GnRH
Hypothalamus GnRH Anterior Pituitary Anterior Pituitary CLFollicle Ovary LH, FSH LH LH, FSH Inhibin (-) Estradiol Progesterone Estradiol (-)
Tonic and Preovulatory Surge of GnRH
Follicular Phase
Hypothalamus GnRH Anterior Pituitary Anterior Pituitary Follicle Ovary LH, FSH Inhibin (-) Estradiol (-) LH Progesterone (-) CL
Estradiol (+) Hypothalamus GnRH Anterior Pituitary Anterior Pituitary Follicle Ovary LH, FSH Inhibin (-) Estradiol
Follicular Phase
Follicular Progression Primordial Primary Secondary Tertiary
Growth and Atresia of Follicles Atresia
Fate of follicles and oocytes. Total # of follicles At birth 100, months 75, 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
Fate of follicles and oocytes. Total # of follicles At birth 100, months 75, 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 100 Days of Gestation 2.9 million Can increase with superovulation with FSH to stimulate the rescue of follicles which would have undergone atresia Can increase with superovulation with FSH to stimulate the rescue of follicles which would have undergone atresia
Gonadotropin Independent FSH Recruitment Initial Follicular Growth Small Antral Follicle days
Follicular Waves in Cattle Ovulation Follicular Size Day After Ovulation FSH Sensitive Pool Recruitment Selection Dominance Atresia
Follicular Waves in Cattle Ovulation Follicular Size Day After Ovulation FSH Sensitive Pool Recruitment Selection Dominance Atresia Progesterone
Follicular Waves in Cattle Ovulation Follicular Size Day After Ovulation Recruitment FSH estradiol (-) Selection FSH estradiol (-) inhibin (-) Dominance FSH estradiol (-) inhibin (-) Atresia estradiol inhibin Progesterone
Follicular Waves in Cattle Ovulation Follicular Size Day After Ovulation Recruitment Selection Dominance Atresia Progesterone
Follicular Waves in Cattle Ovulation Follicular Size Day After Ovulation Progesterone
Follicular Waves in Cattle Ovulation Follicular Size Day After Ovulation Progesterone
Follicular Waves in Cattle Ovulation Follicular Size Day After Ovulation Progesterone Dominance Recruitment Selection Ovulation
Two Follicular Waves 10Ovulation21 Follicular Size Recruitment Selection Dominance Atresia Ovulation Day After Ovulation Progesterone
Follicular Wave Emergence FSH always controls emergence Increase in FSH precedes emergence
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
Gonadotropin Action Within the Follicle
Antral Follicle Granulosa Theca Internal
Theca Interna Granulosa Blood Receptor LH cAMP Cholesterol Testosterone PKA Receptor FSH Testosterone cAMP Estradiol PKA
Theca Interna Granulosa Blood Receptor LH cAMP Cholesterol Testosterone PKA Receptor FSH Testosterone cAMP Receptor LH Selection Dominant Follicle Express LH Receptor cAMP Estradiol PKA
Ovulation
Tunica Albuginea Germinal Epithelium Theca Externa Theca Interna Granulosa Basement Membrane
protein synthesis steroid synthesis prostaglandin synthesis plasminogen activator synthesis Blocking of these events in the follicle prevents ovulation.
Preovulatory LH Surge Ovulation Cumulus Expansion Oocyte Separates From Follicular Wall
Cumulus Expansion Unexpanded Expanded Hyaluronic Acid and Protein Production
Cumulus and Oocyte Separation
Preovulatory LH Surge Ovulation Cumulus Expansion Cumulus Expansion Oocyte Separates From Follicular Wall Oocyte Separates From Follicular Wall Protein Synthesis in and around Follicle Protein Synthesis in and around Follicle Plasminogen Activator Plasminogen Activator Progesterone Prostaglandin Synthesis PGE and PGF Prostaglandin Synthesis PGE and PGF
Preovulatory LH Surge Ovulation Increased Blood Flow to Ovary and Follicle Increased Blood Flow to Ovary and Follicle Vascular Permeability Plasminogen Cumulus Expansion Cumulus Expansion Oocyte Separates From Follicular Wall Oocyte Separates From Follicular Wall Protein Synthesis in and around Follicle Protein Synthesis in and around Follicle Plasminogen Activator Plasminogen Activator Progesterone Prostaglandin Synthesis PGE and PGF Prostaglandin Synthesis PGE and PGF
Preovulatory LH Surge Ovulation Increased Blood Flow to Ovary and Follicle Increased Blood Flow to Ovary and Follicle Vascular Permeability Plasminogen Cumulus Expansion Cumulus Expansion Oocyte Separates From Follicular Wall Oocyte Separates From Follicular Wall Collagenase (inactive) Follicular Wall Weakens Follicular Wall Weakens Plasmin Collagenase (active) Protein Synthesis in and around Follicle Protein Synthesis in and around Follicle Plasminogen Activator Plasminogen Activator Progesterone Prostaglandin Synthesis PGE and PGF Prostaglandin Synthesis PGE and PGF
Preovulatory LH Surge Ovulation Increased Blood Flow to Ovary and Follicle Increased Blood Flow to Ovary and Follicle Vascular Permeability Plasminogen Cumulus Expansion Cumulus Expansion Oocyte Separates From Follicular Wall Oocyte Separates From Follicular Wall Contraction of Smooth Muscle Contraction of Smooth Muscle Collagenase (inactive) Follicular Wall Weakens Follicular Wall Weakens Plasmin Collagenase (active) Protein Synthesis in and around Follicle Protein Synthesis in and around Follicle Plasminogen Activator Plasminogen Activator Progesterone Prostaglandin Synthesis PGE and PGF Prostaglandin Synthesis PGE and PGF
Types of Ovulators
Spontaneous Ovulators
Induced Ovulators
Sensory Neurons Nerve endings sensing copulation Penis Copulation Induced Ovulators
GnRH Blood LH Time (hr) LH Spinal Chord Anterior Pit. Posterior Pit. Hypothalamus Stimulation
Sensory Neurons Nerve endings sensing copulation Penis Copulation LH
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
Oogenesis Primordial Germ Cells Oogonia Primary Oocyte Growth Initiation of Meiosis Interphase DNA synthesis Meiotic prophase begins zona pellucida formation mRNA production protein synthesis cortical granule formation nuclear maturation cytoplasmic maturation Migration to germinal ridge Mitotic divisions Prophase of Meiosis leptotene zygotene pachytene diplotene Meiotic Arrest dictyotene Gonadotropin Independent Gonadotropin Dependent Follicle Cells
Fetal Oocyte Development Fertilization Birth MitosisMeiosis Mouse 19 d Sow 114 d Cow 280 d
Ovulation of Tertiary Follicle
Formation of the Zona Pellucida Corona Radiata Zona Pellucida Oocyte
Corona Radiata Zona Pellucida Oocyte Gap Junctions
OMI - Oocyte Maturation Inhibitor MPF - Maturation promoting factor GV - germinal vesicle (nucleus) pre-MPF MPF GV During Oocyte Growth and Before the LH Surge OMI cAMP Gap Junctions Allow Cell to Cell Communication! cAMP PKA
The LH Surge Gap Junctions are Destroyed!
GV GVBD The LH Surge Resumption of Meiosis Gap Junctions are Destroyed! pre-MPF MPF cAMP PKA
LH Surge Resumption of Meiosis First polar body emitted, arrest at metaphase II of meiosis Ovulation Primary Oocyte Secondary Oocyte Sperm Penetration Zygote (pronucleate egg) 4N 2N N N (most species)
LH Surge Resumption of Meiosis First polar body emitted, arrest at metaphase II of meiosis Ovulation Primary Oocyte Secondary Oocyte Sperm Penetration Zygote (pronucleate egg) 4N 2N N N Ovulation Dog Fox Ovulation Dog Fox Sperm Penetration Dog Fox Sperm Penetration Dog Fox (most species)