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

5

Regression

FSH FSH

Follicle DevelopmentLuteinizing Hormone (LH)

Growth

Selection

Dominance

LH promotes further follicle growth and maturation of egg

6

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