Chapter 7 - Cyclicity

estrous cycle

consist of a series of predictable reproductive events beginning at estrus and ending at the subsequent estrus

• continue throughout adult female’s life and are interrupted by pregnancy, nursing, and by season of year in some species

• provides females with repeated opportunities to copulate and become pregnant

  • the period between one estrus and the next

Estrus

(heat) the period of sexual receptivity

anestrus

period when cyclicity stops

estrus

noun “the cow is displaying ____”

estrous

adjective “the length of the ____ cycle is 21 days”

types of estrous cyclicity

• polyestrus

• seasonally polyestrus

• monoestrus

polyestrus

females can become pregnant throughout the year regardless of season

seasonally polyestrus

females display “clusters” of estrous cycles that occur only during certain seasons of the year

• short day

• long day

short day breeders

begin to cycle as day lengths decrease in autumn

long day breeders

initiates cyclicity as day length increases in the spring

monoestrous

females defined as having one cycle per year

• will have a period of estrus that lasts for several days

follicular phase

period from the regression of corpora lutes to ovulation

• relatively short

• primary ovarian structures are large, growing follicles secreting estradiol

follicular phase

• large astral follicle = primary ovarian structure

  • estradiol (secreted by follicles) = primary hormone

luteal phase

period from ovulation until corpora lute regression

• longer than follicular phase

• dominant ovarian structures are the corpora lute

• primary reproductive hormone is progesterone

  • follicle will continue to grow and regress during this phase

luteal phase

corpora lutea = primary ovarian structure

progesterone (secreted by corpora lutea) = primary hormone

follicular phase

proestrus + estrus

luteal phase

metestrus + diestrus

proestrus

the period immediately proceeding estrus

• begins when progesterone declines as a result luteolysis (destruction of CL)

• terminates the onset of estrus

• major endocrine transition from a period of progesterone dominance to period of estradiol dominance

• astral follicles mature for ovulation and female reproductive system prepares for onset of estrus and mating

estrus

period during which the female allows copulation

• characterized by visible behavioral symptoms such as sexual receptivity and mating

• estradiol is dominant hormone

  • induces profound behavioral alteration

  • causes major physiological changes in reproductive tract

standing estrus

female displaces characteristics of mating posture known as lordosis

proestrus

formation of ovulatory follicles and estradiol secretion

estrus

sexual receptivity and peak estradiol secretion

metestrus

CL formation and beginning progesterone secretion

diestrus

sustained luteal secretion of progesterone

metestrus

transition from estradiol dominance to progesterone dominance

• period between ovulation and formation of functional corpora lutes

• structural remodeling resulting in formation of intraovarian endocrine gland called corpus luteam

diestrus

period of maximum luteal function

• longest stage of estrous cycle

• period when corpus luteum is fully functional and progesterone secretion is high

• ends when corpus luteum is destroyed

• high progesterone prompts uterus to prepare a suitable enviornment for early embryo development and eventually attachment of conceptus to endometrium

anestrus

means without estrus (heat)

• a condition when the female does not exhibit estrous cycles

  • ovaries are relatively inactive and neither ovulatory follicles nor functional corpora lute are present

  • result of insufficient GnRH release from hypothalamus to stimulate and maintain gonadotropin secretion by the pituitary

seasonal anestrus

reduction in the frequency of hypothalamic GnRH secretion

lactational anestrus

cyclicity is completely suppressed during lactation

mammary stimulation

not totally responsible for lactational anestrus

anestrus

can result from negative energy balance

menstrual cycle

defined as the events that occur between the onset of two successive menstrual periods

• ovulation occurs in the middle of cycle

• follicular phase of luteal phase are half and half of cycle

menstruation

sloughing of endometrium to the exterior

amenorrhea

humen equivalent to anestrus caused by:

• menopause

• low nutritional intake

• lactation