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

7. Follicular Phase

8. Follicular Progression
Secondary
Primary
Primordial
Tertiary

9. Growth and Atresia of Follicles

10. 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

11. Initial Follicular Growth
Small Antral Follicle
days
Gonadotropin
Independent
FSH
Recruitment

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

13. 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

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

15. Follicular Waves in Cattle
Progesterone
Dominance
Recruitment
Selection
Ovulation
Follicular Size
FSH, E2 inhibin, LH
FSH, E2 inhibin, LH
FSH, E2
Ovulation 9 16 21
Day After Ovulation

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

17. 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

18. Gonadotropin Action Within the Follicle

19. Antral Follicle
Theca Internal
Granulosa

20. 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

21. Ovulation

22. Germinal Epithelium
Tunica
Albuginea
Theca Externa
Theca Interna
Basement Membrane
Granulosa

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

24. Preovulatory LH Surge Ovulation Cumulus Expansion Oocyte Separates
From
Follicular
Wall
Ovulation

25. Cumulus Expansion Hyaluronic Acid and Protein Production Unexpanded

26. Cumulus and Oocyte
Separation

27. 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

28. Types of Ovulators

29. Spontaneous Ovulators

30. Induced Ovulators

31. Nerve endings sensing copulation
Induced Ovulators
Nerve endings sensing copulation
Sensory Neurons
Penis
Copulation

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

33. Nerve endings sensing copulationLH
Nerve endings sensing copulation
Sensory Neurons
Penis
Copulation

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

35. 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

36. Manipulating Ovulation
Hormonal induction of ovulation
PGF2a
GnRH
Progestins
Superovulation
FSH
eCG

37. Principle of PGF2a Use Regress active corpus luteum
Only effective on day corpus luteum
Not effective on days:
1 - 4 (CL not responsive)
(CL already regressed)

38. Induction of Ovulation with PGF2a
Progesterone
Dominance
Recruitment
Selection
Ovulation
Follicular Size
PGF2
Ovulation 9 16 21
Day After Ovulation

39. Eliminate current follicular wave
Ovsync
GnRH
PGF2
GnRH
hours
Timed AI
7 Days
hours
Eliminate current follicular wave
Luteolysis
Ovulates dominant follicle

40. Use of Progestogens Principle:
Maintain the cow under the influence of progesterone until corpus luteum regresses, remove progesterone -
animal respond to progesterone with estrus and ovulation 2-5 days later.
Administration:
Injection
Feed
Implant
Pessary or Control Internal Drug Release (CIDR)
This does not regress the CL!!!!

41. Stimulating Follicular Development
eCG or FSH
Multiple
Ovulations
Ovulation
Estrus
Estrus
Progesterone
From C.L.
Estrus
eCG or FSH
First Follicular
Wave
10-12
PGF2a 17

42. 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

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

45. Formation of the Zona Pellucida
Corona Radiata
Oocyte
Zona Pellucida

46. Corona Radiata
Zona Pellucida
Oocyte
Gap Junctions

47. 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!

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

49. 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

50. Hormonal Production by Follicles
Recruitment
Estradiol
Selection
Estradiol, Inhibin
Dominant
Estradiol, Inhibin
Atretic
Androgen or No steroid