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