Physiology of Reproduction The Estrous Cycle and the Follicular Phase Dr. Attilio M. de Cosmo Estrous Cycle definition A series of physiological changes in sexual and other organs in female mammals, extending from one period of heat to the next, accompanied by behavioral changes indicating interest in mating. Hormones GnRH (origin Hypothalamus) stimulates FSH and LH release by pituitary gland FSH (anterior pituitary gland) Female: stimulates follicle development and ripening in ovaries Male: stimulates spermatogenesis LH (anterior pituitary gland) Female: stimulates ripening of follicle, induces ovulation, formation and maintenance of corpus luteum in the ovary Male: stimulates testosterone production Hormones Oestrogens (ovary: granulosa cells of the follicle) induces oestrus behaviour. Stimulates pre-ovulatory GnRH release Progesterone (ovary: corpus luteum) prepares the endometrium for nidation of an embryo, maintains pregnancy, decreases GnRH release, thus inhibits new ovulations Prostaglandin F2 (uterus) regression of the corpus luteum steroid synthesis progesterone collagenase theca interna present 1-3 days following ovulation blood vessels in follicle wall rupture walls collapse cells intermix old basement membrane becomes connective tissue of CL increases in size papilla forms composed of cells from the granulosa and theca interna progesterone production increases a small cavity may be present where the folliclular antrum was present Ovulation Oocyte Cumulus Cells Follicular Fluid Luteal Tissue Large cells from granulosa Small cells from the theca interna Progesterone Targets Aveolar Development Blocks Estrus Negative Feedback Luteolysis Uterus PGF2 Oxytocin Prostaglandin F2 Control of Luteolysis Progesterone from CL stimulates production of uterine PGF2 after day 15 in cow Uterine Horn Uterine Vein Prostaglandin synthesis by uterine endometrium is released into the uterine vein. Oviduct Ovary Corpus Luteum PGF2 is picked up by ovarian artery through counter current exchange and delivered back to the ovary where it causes lysis of the CL Uterine Artery Ovarian Pedicle PGF PGF into Artery PGF Not Effective (Cow, Ewe, Mare) PGF Not Effective (Sow) Tonic and Preovulatory Surge of GnRH Hypothalamus GnRH Anterior Pituitary CLFollicle Ovary LH, FSH LH LH, FSH Inhibin (-) Estradiol Progesterone Estradiol (-) (-) Hypothalamus GnRH Anterior Pituitary Follicle Ovary LH, FSH LH, FSH Inhibin (-) Estradiol Estradiol(-) LH Progesterone (-) CL Estradiol(+) Hypothalamus GnRH Anterior Pituitary Follicle Ovary LH, FSH LH, FSH Inhibin (-) Estradiol Follicular Progression Primary Secondary Tertiary Growth and Atresia of Follicles Atresia Total # of follicles At birth 100,000 12 months 75,000 4-6 years 21,000 Aged cow 2,500 Follicles undergo atresia at all stages of development. Maximum number of oocytes ovulated for a cow 17 cycles/year x 8 year = 136 oocytes ovulated / lifespan Fate of follicles and oocytes 100 Days of Gestation 2.9 million Superovulation; rescue follicles from undergoing atresia with FSH treatment. Total # of follicles At birth 100,000 12 months 75,000 4-6 years 21,000 Aged cow 2,500 Follicles undergo atresia at all stages of development. Maximum number of oocytes ovulated for a cow 17 cycles/year x 8 year = 136 oocytes ovulated / lifespan Fate of follicles and oocytes Gonadotropin Independent FSH Recruitment Initial Follicular Growth Small Antral Follicle 50 - 60 days Ovulation Tunica Albuginea Germinal Epithelium Theca Externa Theca Interna Granulosa Basement Membrane protein synthesis steroid synthesis prostaglandin synthesis plasminogen activator synthesis Blocking of these events in the follicle prevents ovulation. Cumulus and Oocyte Separation Preovulatory LH Surge Ovulation Cumulus Expansion Oocyte Separates From Follicular Wall Cumulus Expansion UnexpandedExpanded Hyaluronic Acid and Protein Production Oogonia in Egg Nest Fetal Pig Ovary Oogonia and Primary Oocytes Primary Oocytes in Primordial Follicles Primary Oocyte in Primary Follicle Physiology of Reproduction Reproductive Cycles in the Female Terminology Estrus is a noun. The cow is displaying estrus. Estrous is an adjective. The length of the estrous cycle is 21 days. Oestrus and Oestrous British and European spellings Estrus and Heat are synonymous Terminology (cont.) Anestrus When the female is not having repeated estrous cycles. Types of Cyclicity Polyestrus Relative E2 J F M A M J J A S O N D Queen Cow Sow Types of Cyclicity Seasonally Polyestrus Short day breeders (Fall) Long day breeders (Spring) Relative E2 J F M A M J J A S O N D Relative E2 J F M A M J J A S O N D Type of Cyclicity Monoestrus DogWolfBear Relative E2 J F M A M J J A S O N D Average Reproductive Cycles SpeciesLength of Length ofOvulationLength of Estrous CycleEstrusPregnancy cow21 days18 hr11 hr after282 days