Physiology of ovary
By Alvin Lee
THE OVARIAN CYCLE EVENTS
• A) FOLLICULAR GROWTH• B) OVULATION • C) CORPUS LUTEUM FORMATION• D) CORPUS LUTEUM REGRESSION
Follicle DevelopmentFollicular Wave
Recruitment
Growth
Selection
Dominance
Regression
Next Recruitment
Follicle development occurs as a wave-like pattern consisting of “Recruitment”, “Selection”, “Growth”, “Dominance”, and “Regression” phases Usually 2 to 4 follicular waves occur during the estrous cycle in cattle
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Follicle DevelopmentFollicle Stimulating Hormone (FSH)
Recruitment
Next Recruitment
FSH precedes recruitment of follicles (causes follicles to start growing) FSH is the same hormone used for superovulation and embryo transfer in cattle
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Regression
FSH FSH
Follicle DevelopmentLuteinizing Hormone (LH)
Growth
Selection
Dominance
LH promotes further follicle growth and maturation of egg
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Regression
LH pulses
Follicle Development and OvulationLuteinizing Hormone (LH) and Estrogen
Growth
Selection
Dominance
Estrus
LH Surge
Ovulation
Estrogen
LH stimulates follicle growth and a growing follicle produces high levels of estrogen High levels of estrogen, in turn, cause estrus and surge release of LH that triggers ovulation
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0 2 4 6 8 10 12 14 16 18 20 0
Estru
s
Estru
s
Day of the Estrous Cycle Length of the estrous cycle in cattle with 3 follicular waves is typically 20 to 24 days
Follicle Development During the Estrous CycleExample for 3 Follicular Waves
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Ovulation
Ovulation
Day of the Estrous Cycle0 2 4 6 8 10 12 14 16 18 20 0
Estru
s
Estru
s
Length of the estrous cycle in cattle with 2 follicular waves is typically 18 to 20 days, slightly shorter than the estrous cycle with 3 follicular waves
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Ovulation
Ovulation
Follicle Development During the Estrous CycleExample for 2 Follicular Waves
0 2 4 6 8 10 12 14 16 18 20 0
Estru
s
Estru
s
Day of the Estrous Cycle
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Ovulation
Ovulation
Endocrinology During the Estrous CycleFollicle Stimulating Hormone (FSH)
Example shown for cattle having 3 follicular waves during a 21-day estrous cycle
FSH
0 2 4 6 8 10 12 14 16 18 20 0
Estru
s
Estru
s
Day of the Estrous Cycle Example shown for cattle having 3 follicular waves during a 21-day estrous cycle
11Endocrinology During the Estrous CycleLuteinizing Hormone (LH)
LH SurgeOvulation
Ovulation
LH Surge
LH pulses LH pulses
0 2 4 6 8 10 12 14 16 18 20 0
Estru
s
Estru
s
Day of the Estrous Cycle
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Example shown for cattle having 3 follicular waves during a 21-day estrous cycle
Endocrinology During the Estrous CycleEstrogen
Ovulation
Ovulation
Estrogen
0 2 4 6 8 10 12 14 16 18 20 0
Estru
s
Estru
s
Day of the Estrous Cycle
Growth
Regression
13Corpus Luteum (CL)Growth and Regression
Corpus luteum develops from the ovulated follicle and takes approximately 10 days to reach mature size
Ovulation
0 2 4 6 8 10 12 14 16 18 20 0
Estru
s
Estru
s
Day of the Estrous Cycle Corpus luteum produces progesterone Progesterone is responsible for maintenance of pregnancy after conception occurs
14Corpus Luteum (CL)
Progesterone
Growth
Regression
Progesterone
0 2 4 6 8 10 12 14 16 18 20 0
Estru
s
Estru
s
Corpus Luteum (CL) RegressionProstaglandin F2 (PG)
Day of the Estrous Cycle Late in the estrous cycle, uterus produces PG which causes regression of corpus luteum PG is the same or similar hormone in “Lutalyse®”, “Estrumate®”, “ProstaMate®”, and “In Synch®”
Growth
Regression
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PG
Estru
sCorpus Luteum (CL) Maintenance
When cow becomes pregnant …
Day of the Estrous Cycle
Presence of embryo blocks uterus to produce PG late in the estrous cycle which causes maintenance of corpus luteum and production of progesterone for pregnancy
PG
Maintenance
0 2 4 6 8 10 12 14 16 18 20 0
Embryo
Growth
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Progesterone regulates LH PulsesLuteinizing Hormone (LH)
0 2 4 6 8 10 12 14 16 18 20 0
Estru
s
Estru
s
Day of the Estrous Cycle
LH Surge
Progesterone regulates secretion pattern of LH pulses and hence, follicular development
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Progesterone
LH pulses LH pulses
Endocrinology of the Estrous Cycle
0 2 4 6 8 10 12 14 16 18 20 0
Estru
s
Estru
s
Day of the Estrous Cycle
Estrogen
Progesterone PG
Relationships among estrogen, progesterone, and PG during the 21-day estrous cycle
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Physiology and Endocrinologyof the Estrous Cycle
0 2 4 6 8 10 12 14 16 18 20 0
Estru
s
Estru
s
Day of the Estrous Cycle
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Relationships among structural and hormonal changes during the 21-day estrous cycle (example shown for cattle having 3 follicular waves)
SUMMARY OF OVARIAN CYCLE EVENTS
A) FOLLICULAR GROWTH-after regression of CL, (caused by PGF2a), FSH↑ and LH↑ ①LH stimulates secretion of androgens in the theca interna, which diffuse into granulosa cells②FSH stimulate: i)conversion of androgens →oestrogen ii)Formation of LH receptors on granulosa cells- Estrogen-rich fluid formed by granulosa
cells separates the granulosa cells and forms pocket known as ANTRUM
- ↑ of oestrogen causes preovulatory LH SURGE!!
B) OVULATION - LH SURGE!!:i)promotes maturation of oocytes by resuming meiosis through 1st polar body stageii) promotes intrafollicular production of PGA & PGE → rupture of follicle - Formation of mutivesicular bodies (MVB) as
outpockets of exposed theca externa- MVB secrete proteolytic enzyme → digest
ground substance cementing the theca externa fibroblast, allowing oocyte to escape (OVULATION)
C) CORPUS LUTEUM FORMATION-LH SURGE causes FSH receptors number↓ in granulosa cells causing conversion of androgens →oestrogen to ↓,-LH attaches to receptors in granulosa cells (currently corpus luteum) to produce progesterone-as progesterone↑, FSH ↓ and LH ↓
D) CORPUS LUTEUM REGRESSION- progesterone↓, causes FSH ↑ and LH ↑,hence cycle is repetead