Animal Science 434 The Follicular Phase of the
- Slides: 62
Animal Science 434 The Follicular Phase of the Estrous Cycle
Preovulatory Gn. RH Surge Tonic Gn. RH Release Hours Gn. RH (pg/ml) Tonic and Preovulatory Surge of Gn. RH Hours
Hypothalamus Progesterone (-) Gn. RH Estradiol (-) Anterior Pituitary Inhibin (-) LH, FSH LH CL Estradiol LH, FSH Ovary Follicle
Preovulatory Gn. RH Surge Tonic Gn. RH Release Hours Gn. RH (pg/ml) Tonic and Preovulatory Surge of Gn. RH Hours
The Follicular Phase
Hypothalamus Progesterone (-) Gn. RH Estradiol (-) Anterior Pituitary Start of Follicular Phase Inhibin (-) LH, FSH LH CL Estradiol LH, FSH Ovary Follicle
Hypothalamus Gn. RH Estradiol (-) Anterior Pituitary CL Regression Inhibin (-) LH, FSH Estradiol LH, FSH Ovary Follicle
Hypothalamus Gn. RH Ends in LH surge and ovulation Estradiol (+) Anterior Pituitary Inhibin (-) LH, FSH Estradiol LH, FSH Ovary Follicle
The Follicular Phase
Primary Primordial Follicular Progression Tertiary Secondary
Growth and Atresia of Follicles Atresia
Fate of follicles and oocytes At birth 100, 000 12 months 75, 000 4 -6 years 21, 000 Aged cow 2, 500 100 Days of Gestation 2. 9 million • 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 Superovulation or Ovum Pick-up (OPU) - rescue some follicles from atresia
Initial Follicular Growth Small Antral Follicle 50 - 60 days Gonadotropin Independent FSH Recruitment
Follicular Waves in Cattle
Follicular Size Atresia Recruitment Dominance Ovulation Selection FSH Sensitive Pool Ovulation 9 Day 16 21
Follicular Size Atresia Recruitment Dominance Progesterone Ovulation Selection FSH Sensitive Pool Ovulation 9 Day 16 21
Follicular Size Progesterone Atresia Ovulation FSH Dominance Selection FSH Recruitment 9 FSH Day estradiol inhibin FSH estradiol (-) inhibin (-) estradiol (-) 16 21
Follicular Size Progesterone Atresia Dominance Selection Recruitment Ovulation 9 Day 16 21
Follicular Size Progesterone Ovulation 9 Day 16 21
Follicular Size Progesterone Ovulation 9 Day 16 21
Progesterone Follicular Size Ovulation Dominance Selection Recruitment Ovulation 9 Day 16 21
Two Follicular Waves
Follicular Size Progesterone Atresia Dominance Ovulation Selection Recruitment Ovulation 10 Day 21
Follicular Wave Emergence • Recruitment = Emergence • FSH always controls emergence • Increase in FSH precedes emergence
Species Variation in Follicular Waves • • • Cattle - 2 or 3 / cycle Cl-progesterone Sheep - 4 or 5 / cycle Pigs - 1 / cycle Cl-progesterone, inhibin Horses - 1 / cycle If first wave Human - 1 / cycle stops/fails, then a second wave emerges!!!
Gonadotropin Action Within the Follicle
Antral Follicle Theca Internal Granulosa
Theca Interna LH Receptor c. AMP Cholesterol FSH d Testosterone Receptor Bloo PKA c. AMP Test. Granulosa Estradiol PKA
Theca Interna Selection Dom. Foll. Express LH Receptor c. AMP Cholesterol FSH PKA Testosterone Receptor c. AMP LH Receptor c. AMP Test. PKA Granulosa Estradiol d Receptor Bloo LH
Ovulation
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
Preovulatory LH Surge Cumulus Expansion Oocyte Separates From Follicular Wall Ovulation
Cumulus Expansion Hyaluronic Acid and Protein Production Unexpanded Expanded
Cumulus and Oocyte Separation
Preovulatory LH Surge Cumulus Expansion Protein synthesis changes in and around Follicle Progesterone Plasminogen Activator Oocyte Separates From Follicular Wall Ovulation Prostaglandin Synthesis PGE and PGF
Preovulatory LH Surge Cumulus Expansion Protein synthesis changes in and around Follicle Progesterone Plasminogen Activator Oocyte Separates From Follicular Wall Histamine, PGE 2 Increased Blood Flow to Ovary and Follicle Vascular Prostaglandin Permeability Synthesis PGE and PGF Plasminogen Edema Ovulation Foll. pressure
Preovulatory LH Surge Cumulus Expansion Protein synthesis changes in and around Follicle Progesterone Plasminogen Activator Oocyte Collagen. (inact. ) Plasmin Separates From Collagenase (act. ) Follicular Wall Weakens Wall Ovulation Histamine, PGE 2 Increased Blood Flow to Ovary and Follicle Vascular Prostaglandin Permeability Synthesis PGE and PGF Plasminogen Edema Foll. pressure
Preovulatory LH Surge Cumulus Expansion Protein synthesis changes in and around Follicle Progesterone Plasminogen Activator Oocyte Collagen. (inact. ) Plasmin Separates From Collagenase (act. ) Follicular Wall Weakens Wall Ovulation Histamine, PGE 2 Increased Blood Flow to Ovary and Follicle Vascular Prostaglandin Permeability Synthesis PGE and PGF Plasminogen Contraction Sm. Muscle Edema Foll. pressure
Types of Ovulators
Spontaneous Ovulators
Induced Ovulators
Induced Ovulators Nerve endings sensing copulation Copulation Sensory Neurons Penis
Blood LH Hypothalamus LH Time (hr) Stimulation Gn. RH Posterior Pit. Anterior Pit. Spinal Chord
Induced Ovulators LH Nerve endings sensing copulation Copulation Sensory Neurons Penis
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 Move to germinal ridge Mitotic divisions Primordial Germ Cells Oogonia Follicle Cells Meiosis Interphase DNA synthesis Meiotic prophase Primary Oocyte Prophase of Meiosis Leptotene, Zygotene Pacytene, Diplotene Dictyotene Meiotic Arrest
Gonadotropin Independent Gonadotropin Dependent Growth zona pellucida formation m. RNA production Protein synthesis Cortical granule formation nuclear maturation cytoplasmic maturation Remains primary oocyte until LH surge
Oogonia in Egg Nest Fetal Pig Ovary
Oogonia Primary Oocytes
Primary Oocytes in Primordial Follicles
Primary Oocyte in Primary Follicle
Fetal Oocyte Development Fertilization Mitosis Meiosis Birth Cow 280 d Sow 114 d Mouse 19 d
Ovulation of Tertiary Follicle
Corona Radiata Formation of the Zona Pellucida Oocyte
Corona Radiata Zona Pellucida Oocyte Gap Junctions
During Oocyte Growth and Before the LH Surge • OMI - Oocyte Maturation Inhibitor • MPF - Maturation promoting factor c. AMP OMI c. AMP GV PKA pre-MPF • GV - germinal vesicle (nucleus) Gap Junctions Allow Cell to Cell Communication!
The LH Surge Gap Junctions are Destroyed!
The LH Surge c. AMP GVBD PKA Resumption of Meiosis GV pre-MPF Gap Junctions are Destroyed!
LH Surge Resumption of Meiosis 4 N 4 N 2 N Ovulation (most species) Secondary Oocyte Primary Oocyte N N Zygote (pronucleate egg) First polar body emitted, arrest at metaphase II 2 N Sperm Penetration
LH Surge Resumption of Meiosis 4 N 4 N Primary Oocyte Ovulation • Dog, Fox Zygote (pronucleate egg) First polar body emitted, arrest at metaphase II 2 N Ovulation (most species) Sperm Pen. Secondary • Dog, Fox Oocyte N N 2 N Sperm Penetration
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