1. The Follicular Phase of the Estrous Cycle
Animal Science 434
The Follicular Phase of the Estrous Cycle

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

3. Tonic and Preovulatory Surge of GnRH

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

5. Steps Leading to the Preovulatory LH Surge
P4 from Cl
 GnRH
FSH and LH
Inhibin
 FSH
Proestrual
Follicular
Development
Preovulatory
LH surge
 Estradiol
to threshold

6. Relationship of Hypothalamus, Anterior Pituitary and Ovary
In the Absence of Progesterone

7. Tonic and Preovulatory Surge of GnRH

8. Hormone Changes During the Folliclular Phase
Progesterone LH
FSH
Estradiol

9. Follicle Progression

10. Growth and Atresia of Follicles

11. Follicular Growth Recruitment Gonadotropin Independent Small Antral
Follicle
Recruitment
Initiated by FSH

12. Progesterone
FSH
FSH
FSH E2
Inhibin
Inhibin LH LH
Deviation!!!

13. Folliclular Waves in Cattle

15. Follicular Waves

16. Follicular Waves

17. Growing Phase Initial growth (recruitment) is under influence of FSH
Inhibin secreted to decrease FSH and development of subordinate follicles (estrogen also; selection)
Dominant follicle becomes less dependent on FSH for growth
FSH induces LH receptors in granulosa
Dominant follicle produces estradiol and androgens in response to LH and FSH
Androgens, lack of FSH may cause subordinate follicles to become atretic (dominance)

18. Static Phase Inhibin production stops
FSH increase stimulates follicular wave
Estradiol from dominant follicle decreases and androgens increase, this may initiate atresia of dominant follicle

19. Regressing Phase
Dominant follicle becomes atretic and looses steroidogenic capability

20. Follicular Waves

21. Growing Phase Initial growth (recruitment) is under influence of FSH
Inhibin secreted to decrease FSH and development of subordinate follicles (estrogen also; selection)
Dominant follicle becomes less dependent on FSH for growth
FSH induces LH receptors in granulosa
Dominant follicle produces estradiol and androgens in response to LH and FSH
Androgens, lack of FSH may cause subordinate follicles to become atretic (dominance)

22. Growing Phase
LH continues to increase in response to estradiol positive feedback in the absence of progesterone
Dominant follicle increases in size and estrogen production
LH surge occurs to trigger ovulation of the dominant follicle

23. Hormone Changes During the Folliclular Phase
Ovulation
Follicular Phase
Progesterone LH
FSH
Estradiol

24. Two Follicular Waves Follicular Size Day After Ovulation Dominance
Atresia
Ovulation
Selection
(Deviation)
Recruitment
Ovulation 10 21
Day After Ovulation

25. Three Follicular Waves
Follicular Size
Ovulation
Ovulation 9 16 21
Day After Ovulation

26. Follicular Waves

27. 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

28. Gonadotropin Action Within the Follicle

29. Theca Interna
Granulosa

30. 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

31. Ovulation

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

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

34. Pathways of Ovulation (granulosa) increased cyclic AMP Increased blood
flow to follicle LH
Mature follicle
Protein synthesis
Cumulus cell production
of hyaluronic acid
and proteins
Increased vascular
permeability of
follicle
(cellular differentiation)
Steroid biosynthesis
Prostaglandin
biosynthesis
(PGE and PGF )
Cumulus expansion
Progesterone 2 2
Plasminogen
activator
Separation of cumulus
and oocyte from
granulosa cells
(granulosa)
Plasmin
(protease)
Increased plasminogen
in tissue and follicular
fluid
Inactive
Collagenase
(theca)
Active
Collagenase
Breakdown of theca and tunica albuginea
collagen and tensile strength of follicle wall
Follicle ruptures with only a slight
increase in follicular pressure
PGF
stimulates smooth
muscle contractions
around follicle
Expulsion of follicular
contents

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

36. Cumulus Expansion Hyaluronic Acid and Protein Production Unexpanded

37. Cumulus and Oocyte
Separation

38. 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

39. Types of Ovulators

40. Spontaneous Ovulators

41. Induced Ovulators

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

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

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

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

46. 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

47. Manipulating Ovulation
will cover latter in class

48. 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

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

50. Corona Radiata
Oocyte
Cortical Granules
Zona Pellucida
Gap Junctions
Cortical Granules

51. 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!

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

53. 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