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Lecture 10: The Follicular Phase of the Estrous Cycle

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1 Lecture 10: The Follicular Phase of the Estrous Cycle
Animal Science 434 Lecture 10: The Follicular Phase of the Estrous Cycle

2 Tonic and Preovulatory Surge of GnRH

3 Hypothalamus Progesterone Estradiol (-) (-) GnRH Anterior Pituitary Inhibin (-) LH, FSH Estradiol LH, FSH LH CL Follicle Ovary

4 Tonic and Preovulatory Surge of GnRH

5 Follicular Phase

6 Hypothalamus LH Progesterone (-) CL Estradiol (-) GnRH Anterior Pituitary Inhibin (-) LH, FSH Estradiol LH, FSH Follicle Ovary

7 Hypothalamus Estradiol (+) GnRH Anterior Pituitary Inhibin (-) LH, FSH Estradiol LH, FSH Follicle Ovary

8 Follicular Phase

9 Follicular Progression
Secondary Primary Primordial Tertiary

10 Growth and Atresia of Follicles

11 Fate of follicles and oocytes.
Total # of follicles At birth ,000 12 months ,000 4-6 years ,000 Aged cow ,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

12 Fate of follicles and oocytes.
Total # of follicles At birth ,000 12 months ,000 4-6 years ,000 Aged cow ,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

13 Initial Follicular Growth
Small Antral Follicle days Gonadotropin Independent FSH Recruitment

14 Follicular Waves in Cattle
Atresia Follicular Size Recruitment Dominance Ovulation Selection FSH Sensitive Pool Ovulation 9 16 21 Day After Ovulation

15 Follicular Waves in Cattle
Progesterone Atresia Follicular Size Recruitment Dominance Ovulation Selection FSH Sensitive Pool Ovulation 9 16 21 Day After Ovulation

16 Follicular Waves in Cattle
Progesterone Atresia estradiol inhibin Follicular Size Dominance FSH estradiol (-) inhibin (-) Selection FSH estradiol (-) inhibin (-) Recruitment FSH estradiol (-) Ovulation 9 16 21 Day After Ovulation

17 Follicular Waves in Cattle
Progesterone Follicular Size Atresia Dominance Selection Recruitment Ovulation 9 16 21 Day After Ovulation

18 Follicular Waves in Cattle
Progesterone Follicular Size Ovulation 9 16 21 Day After Ovulation

19 Follicular Waves in Cattle
Progesterone Follicular Size Ovulation 9 16 21 Day After Ovulation

20 Follicular Waves in Cattle
Progesterone Dominance Recruitment Selection Ovulation Follicular Size Ovulation 9 16 21 Day After Ovulation

21 Two Follicular Waves Follicular Size Day After Ovulation Progesterone
Dominance Follicular Size Atresia Ovulation Selection Recruitment Ovulation 10 21 Day After Ovulation

22 Follicular Wave Emergence
FSH always controls emergence Increase in FSH precedes emergence

23 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

24 Gonadotropin Action Within the Follicle

25 Antral Follicle Theca Internal Granulosa

26 Theca Interna Granulosa LH Receptor cAMP Cholesterol PKA Testosterone
Blood Receptor LH cAMP Cholesterol Testosterone PKA Testosterone Receptor FSH cAMP Estradiol PKA

27 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

28 Ovulation

29 Germinal Epithelium Tunica Albuginea Theca Externa Theca Interna Basement Membrane Granulosa

30 Blocking of these events in the follicle prevents ovulation.
protein synthesis steroid synthesis prostaglandin synthesis plasminogen activator synthesis

31 Preovulatory LH Surge Ovulation Cumulus Expansion Oocyte Separates
From Follicular Wall Ovulation

32 Cumulus Expansion Hyaluronic Acid and Protein Production Unexpanded

33 Cumulus and Oocyte Separation

34 Prostaglandin Synthesis
Preovulatory LH Surge Cumulus Expansion Oocyte Separates From Follicular Wall Protein Synthesis in and around Follicle Plasminogen Activator Progesterone Prostaglandin Synthesis PGE and PGF Ovulation

35 Vascular Permeability Prostaglandin Synthesis
Preovulatory LH Surge Cumulus Expansion Oocyte Separates From Follicular Wall Increased Blood Flow to Ovary and Follicle Vascular Permeability Plasminogen Protein Synthesis in and around Follicle Plasminogen Activator Progesterone Prostaglandin Synthesis PGE and PGF Ovulation

36 Vascular Permeability Prostaglandin Synthesis
Preovulatory LH Surge Cumulus Expansion Oocyte Separates From Follicular Wall Increased Blood Flow to Ovary and Follicle Vascular Permeability Plasminogen Protein Synthesis in and around Follicle Plasminogen Activator Progesterone Prostaglandin Synthesis PGE and PGF Collagenase (inactive) Follicular Wall Weakens Plasmin Collagenase (active) Ovulation

37 Vascular Permeability Prostaglandin Synthesis
Preovulatory LH Surge Cumulus Expansion Oocyte Separates From Follicular Wall Increased Blood Flow to Ovary and Follicle Vascular Permeability Plasminogen Protein Synthesis in and around Follicle Plasminogen Activator Progesterone Prostaglandin Synthesis PGE and PGF Collagenase (inactive) Follicular Wall Weakens Plasmin Collagenase (active) Contraction of Smooth Muscle Ovulation

38 Types of Ovulators

39 Spontaneous Ovulators

40 Induced Ovulators

41 Nerve endings sensing copulation
Induced Ovulators Nerve endings sensing copulation Sensory Neurons Penis Copulation

42 Hypothalamus Blood LH Time (hr) GnRH Posterior Pit. Stimulation LH Anterior Pit. Spinal Chord

43 Nerve endings sensing copulation
LH Nerve endings sensing copulation Sensory Neurons Penis Copulation

44 Cats Induced Ovulators Single copulation Only works 50% of the time
Multiple copulations Higher LH surge

45 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

46 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

47 Primordial Follicles in Fetal Pig Ovary

48 Oogonia

49 Primary Oocytes in Primordial Follicles

50 Oogonia and Primary Oocytes

51 Primary Oocyte in Primary Follicle

52 Fetal Oocyte Development
Mitosis Meiosis Fertilization Birth Cow 280 d Sow 114 d Mouse 19 d

53 Ovulation of Tertiary Follicle

54 Formation of the Zona Pellucida
Corona Radiata Oocyte Zona Pellucida

55 Corona Radiata Zona Pellucida Oocyte Gap Junctions

56 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!

57 The LH Surge Gap Junctions are Destroyed!

58 Gap Junctions are Destroyed!
The LH Surge cAMP Resumption of Meiosis GVBD PKA GV pre-MPF MPF Gap Junctions are Destroyed!

59 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

60 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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