Physiology of ovary

THE OVARIAN CYCLE EVENTS A) FOLLICULAR GROWTH B) OVULATION C) CORPUS LUTEUM FORMATION D) CORPUS LUTEUM REGRESSION

Follicle Development Follicular Wave 4 Follicle Development Follicular Wave Dominance Regression Growth Selection Next Recruitment 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

Follicle Development Follicle Stimulating Hormone (FSH) 5 Follicle Development Follicle Stimulating Hormone (FSH) Regression Next Recruitment Recruitment FSH FSH FSH precedes recruitment of follicles (causes follicles to start growing) FSH is the same hormone used for superovulation and embryo transfer in cattle

Follicle Development Luteinizing Hormone (LH) 6 Follicle Development Luteinizing Hormone (LH) Regression Dominance Growth Selection LH pulses LH promotes further follicle growth and maturation of egg

7 Follicle Development and Ovulation Luteinizing Hormone (LH) and Estrogen Ovulation Dominance Estrogen Growth Estrus Selection LH Surge 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

Day of the Estrous Cycle 8 Follicle Development During the Estrous Cycle Example for 3 Follicular Waves Ovulation Ovulation Estrus Estrus 2 4 6 8 10 12 14 16 18 20 Day of the Estrous Cycle Length of the estrous cycle in cattle with 3 follicular waves is typically 20 to 24 days

Day of the Estrous Cycle 9 Follicle Development During the Estrous Cycle Example for 2 Follicular Waves Ovulation Ovulation Estrus Estrus 2 4 6 8 10 12 14 16 18 20 Day of the Estrous Cycle 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

Day of the Estrous Cycle 10 Endocrinology During the Estrous Cycle Follicle Stimulating Hormone (FSH) Ovulation Ovulation Estrus Estrus FSH 2 4 6 8 10 12 14 16 18 20 Day of the Estrous Cycle Example shown for cattle having 3 follicular waves during a 21-day estrous cycle

Endocrinology During the Estrous Cycle Luteinizing Hormone (LH) 11 Endocrinology During the Estrous Cycle Luteinizing Hormone (LH) Ovulation Ovulation LH Surge LH Surge Estrus Estrus LH pulses LH pulses 2 4 6 8 10 12 14 16 18 20 Day of the Estrous Cycle Example shown for cattle having 3 follicular waves during a 21-day estrous cycle

Endocrinology During the Estrous Cycle Estrogen 12 Endocrinology During the Estrous Cycle Estrogen Ovulation Ovulation Estrus Estrogen Estrus 2 4 6 8 10 12 14 16 18 20 Day of the Estrous Cycle Example shown for cattle having 3 follicular waves during a 21-day estrous cycle

Corpus Luteum (CL) Growth and Regression 13 Corpus Luteum (CL) Growth and Regression Ovulation Growth Regression Estrus Estrus 2 4 6 8 10 12 14 16 18 20 Day of the Estrous Cycle Corpus luteum develops from the ovulated follicle and takes approximately 10 days to reach mature size

Corpus Luteum (CL) Progesterone 14 Corpus Luteum (CL) Progesterone Growth Regression Estrus Estrus Progesterone 2 4 6 8 10 12 14 16 18 20 Day of the Estrous Cycle Corpus luteum produces progesterone Progesterone is responsible for maintenance of pregnancy after conception occurs

Corpus Luteum (CL) Regression Prostaglandin F2 (PG) 15 Corpus Luteum (CL) Regression Prostaglandin F2 (PG) Growth Regression Estrus Estrus PG 2 4 6 8 10 12 14 16 18 20 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®”

Corpus Luteum (CL) Maintenance When cow becomes pregnant … 16 Corpus Luteum (CL) Maintenance When cow becomes pregnant … Growth Maintenance Estrus PG Embryo 2 4 6 8 10 12 14 16 18 20 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

Progesterone regulates LH Pulses Luteinizing Hormone (LH) 17 Progesterone regulates LH Pulses Luteinizing Hormone (LH) LH pulses LH pulses LH Surge Estrus Estrus Progesterone 2 4 6 8 10 12 14 16 18 20 Day of the Estrous Cycle Progesterone regulates secretion pattern of LH pulses and hence, follicular development

Endocrinology of the Estrous Cycle 18 Endocrinology of the Estrous Cycle Progesterone PG Estrogen Estrus Estrus 2 4 6 8 10 12 14 16 18 20 Day of the Estrous Cycle Relationships among estrogen, progesterone, and PG during the 21-day estrous cycle

Physiology and Endocrinology of the Estrous Cycle 19 Physiology and Endocrinology of the Estrous Cycle Estrus Estrus 2 4 6 8 10 12 14 16 18 20 Day of the Estrous Cycle 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 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 cells ②FSH 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 stage ii) 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