Ch. 7 - Reproductive Cyclicity
Estrous Cycle
Each cycle consists of a follicular phase and a luteal phase
Menstrual Cycle
At the conclusion of the luteal phase in the menstrual cycle, the endometrium is sloughed to the exterior (menstration)
Consists of the physiologic events that occur between successive periods of sexual receptivity (estrus or heat) and/or ovulations
Follicular Phase: dominated by estradiol secreted by ovarian follicles
- Estradiol causes marked changes in the female tract and initiates sexual receptivity
Luteal Phase: dominated by progesterone from the corpus luteum that prepares the reproductive tract for pregnancy
Anestrus: periods of time when estrous cycles cease
Causes:
Season of the year
Lactation
Pregnancy
Certain forms of stress
Pathology
Consists of the physiological events that occur between successive menstrual periods
3 distinct phases that reflect the condition of the uterine endometrium
Phase 2 - Proliferative Phase: follicles develop and secrete estradiol
- The endometrium begins to grow and increases in thickness
Phase 3 - Secretory Phase dominated by the corpus luteum that secretes progesterone and estradiol
- Endometrium grows and thickens in response to progesterone
- Luteal phase
Phase 1 - Menses: endometrium is sloughed to the exterior
- Follicular phase
Amenorrhea: lack of menstrual periods from the same causes as anestrus
Estrous: adjective - pertaining to estrus
Estrus: noun - period of sexual receptiviy
Three types of estrus cyclicity
Seasonally Polyestrous: dislpay clusters of estrous cycles that occur only during a certain season of the year
Monoestrous: have only one cycle per year
Polyestrous: cycle throughout the year
Short day breeders
- Sheep and goats
Long day breeders
- Horses
Large antral follicles are present - primary ovarian structure
Estradiol (secreted by follicles) is the primary hormone
Corpora lutea is the primary ovarian structure
Progesterone (secreted by corpora lutea) is the primary hormone
Proestrous and estrus
Metestrus and diestrus
Divided into 4 stages
Estrus
Metestrus
Proestrus
Diestrus
Period immediately preceding estrus
Formation of ovulatory follicles and estradiol secretion
Sexual receptivity and peak estradiol secretion
When the female allows copulation
CL formation and begining of progesterone secretion
Transition from estradiol dominance to progesterone dominance
Sustained luteal secretion of progesterone
Period of maximum luteal function
Apparent Anestrus: failure to detect estrus or failure to recognize pregnancy
True Anestrus: insufficient hormonal stimuli
Gestational Anestrus: normal condition brought about by inhibition of GnRH by progesterone
Seasonal Anestrus: prevents females from conceiving during periods of the year when survival of the developing embryo and the neonate would be low
Lactational Anestrus: prevents a new pregnancy before young are weaned
Includes nutritional stress - lack of proper nutrition
Differences from estrous cycle
A period of endometrial sloughing called menstration
The timeline for description of the cycle begins with menses, not ovulation or estrus
No defined period of sexual receptivity