Exam 2: Lecture 22: Female Cyclicity Flashcards
What is estrous?
-Length of estrous cycle
What is estrus?
-Period of sexual receptivity
What is Estrous cycle?
-Consists of series of predictable reproductive events beginning at estrus & ending at subsequent estrus
What is anestrus?
-Not cycling
What is estrual?
-Used to identify a condition related to estrus
What is parturition?
-Giving birth
What is uterine involution?
-Acquisition of normal uterine size & function
How are estrous cycles categorized?
-According to frequency of occurrence throughout the year
What are the 3 types of estrous cycles?
- Polyestrus
- Seasonally Polyestrus
- Monoestrus
What is polyestrus?
-Have uniform distribution of estrous cycles throughout the entire year
-Cattle swine, rodents
What is seasonally polyestrus?
-Have “clusters” of estrous cycles that occur only during certain season of the year
-Short-day breeders (cycle as day length is decreased)
-Long-day breeders (Cycle as day length increases)
What animals are short-day breeders?
-Sheep
-Goat
-Deer
-Elk
What animals are long-day breeders?
-Mares
What is monoestrus?
-Have only one cycle per year
-Dogs, wolves, foxes, bears
-(Domestic dogs typically have 3 estrous cycles per 2 years, but are classified as monoestrus)
What are the 2 major phases of the estrous cycle?
-Follicular phase
-Luteal phase
What is the follicular phase?
-Primary ovarian structure = large follicle(s)
-Primary hormone = estradiol
-Period from CL regression to ovulation
What is the luteal phase?
-Primary ovarian structure = CL
-Primary hormone = Progesterone (secreted by CLs)
-Period from ovulation to CL regression
-Follicles continue to grow/regress, but do not produce high quantities of estradiol
The luteal phase is everything between
Follicular phases
What are the 4 stages of the estrous cycle?
- Proestrus
- Estrus
- Metestrus
- Diestrus
What is proestrus?
-Begins when progesterone declines as result of luteolysis & ends at onset of estrus
-2-5 days (depends on species)
-Characterized by major endocrine transition (progesterone to estradiol)
-Primary hormones: pituitary gonadotropins, FSH & LH
-Antral follicles mature for ovulation & tract prepares for estrus & mating
What is estrus?
-Female sexual receptivity (Characterized by visible behavioral symptoms so often most recognizable stage)
-Peak Estradiol secretion (by dominant follicle)
-Duration varies between species
What is metestrus?
-CL formation (luteinization)
-Beginning of progesterone secretion
-Transition from Estradiol dominance to Progesterone dominance
What is diestrus?
-Sustained secretion of high levels of progesterone from mature CLs
-Longest stage of estrous cycle
-Ends w/ luteolysis
What are the exceptions to the “normal” estrous cycle?
-Estrous cycle of bitch & queen
What is the estrous cycle of the queen?
-Proestrus
-Estrus
-Postestrus (interests period in queen not mated - no ovulation, period of ~7-10 days)
-Diestrus (about same length as gestation)
-Anestrus
What is anestrus?
-“Without cyclicity”
-Females that do not exhibit regular estrous cycles
What are the causes of anestrus?
-Pregnancy
-Lactation (NOT CATS! Queens come back into heat within days of parturition)
-Presence of offspring
-Season (photoperiod)
-Stress
-Pathology
What are 2 reasons for anestrus?
-True anestrus
-Apparent anestrus
What is true anestrus?
-Insufficient hormonal stimulus
-Factors: poor nutrition, stress, pathology
What is apparent anestrus?
-Failure to detect estrus
-Failure to recognize that a female is pregnant
What is a normal condition brought about by inhibition of GnRH by progesterone?
-Gestational anestrus
What should ALWAYS be on a differential list for anestrus?
-Gestational anestrus
Lactational anestrus DOES NOT happen in
-Cats
-Mares
-Alpacas or llamas
-Dairy cows
What is lactational anestrus?
-Lasts for variable amounts of time
-Cyclicity is completely suppressed during lactation in the sow
In suckled cows, cyclicity is delayed as much as
-60 days (suppression of LH)
-Duration is influenced by suckling sessions
Dairy cows typically do not display a ____ anestrus, because
-Lactational anestrus
-Because calf is removed
Beef cows typically have at least a ____ lactational anestrus
60 day
When in lactational anestrus is the amplitude & pulse frequency of blood LH low and the cow remains in anestrus?
-When the number of suckling sessions is between 3 and 20 per day
When in lactational anestrus is the amplitude and frequency of LH increases dramatically and she will begin to cycle?
-When the number suckling sessions is limited to 2 or less per day
Can suckling be totally responsible for suppressing LH in the postpartum cow?
-No
-Mammary stimulation is not totally responsible for lactational anestrus
-Presence of the calf has some effect
Seasonal anestrus is a _____ condition
NORMAL CONDITION
Seasonal anestrus enables the animals to
-Carry developing fetus during favorable time
-Give birth during an advantageous time for newborn
In seasonal anestrus, how does the animal come back to cyclicity?
-Modified by photoperiod to come back to cyclicity (similar to onset of puberty)
What can induce anestrus?
Negative energy balance
-When animal is starved, repro. system is 1st to shut down
-Females consuming low quantities of energy or protein often have sustained periods of anestrus
-In lactating animals, lack of nutrition will prolong lactational anestrus
Estrous is ____, estrus is ____
Estrous is the cycle, estrus is the stage of the cycle
What is folliculogenesis?
-Process where immature follicles develop into more advanced follicles & become candidates for ovulation
-Happens in a wave like pattern
What are the primary ovarian structures in folliculogenesis?
-Primary follicles
-Secondary follicles
-Antral (tertiary) follicles
-Corpus Luteum
-Corpora albicans
What is corpora albicans?
-White in color
-Scar that’s left when corpus luteum regresses
The follicular phase consists of
-Proestrus
-Estrus
The follicular phase is governed by
-Hypothalamus, anterior pituitary, and ovary through secretion of Estradiol in the absence of Progesterone
What are the 4 significant events in the Follicular phase?
- Gonadotropin (FSH & LH) released from anterior lobe of pituitary
- Follicular preparation (growth) for ovulation
- Sexual receptivity
- Ovulation (LH)
What is the dominant hormone in the follicular phase and what does it do?
-Estrogen is dominant hormone
-Changes in repro. tract, behavioral changes, controls onset of preovulatory LH surge
What is the key players in the follicular phase and what does it do?
Tonic center of hypothalamus
-Releases small amplitude pulses of GnRH that stimulate release of FSH & LH from anterior pituitary
-Cause growth & development of follicles on ovaries which produce Estrogen
Surge center of Hypothalamus
-Positive feedback fashion to increasing levels of Estrogen in absence of Progesterone, which causes a release of LARGE quantity of GnRH which causes release of LH
-Results in ovulation
What happens to the surge center once Estrogen reaches a threshold level?
-Surge center is “turned on”
What are the primary steps leading to preovulatory LH surge?
Decreased P4 from CL -> increased GnRH -> increased FSH & LH -> proestrual follicular development
Estradiol exerts a ____ feedback on hypothalamus that drives the surge release of GnRH
Positive feedback
Later in the follicular phase, follicles secrete inhibin that causes a _____ feedback on FSH secretion & what else affects FSH secretion here?
-Negative feedback
-Estrogen is also thought to suppress FSH secretion
What are the 2 groups of GnRH neurons in the hypothalamus?
- Surge center
- Tonic center
The tonic center is like _____, while the surge center is like _____
Faucet dripping, faucet on full blast
Summarize the preovulatory hormonal events
-Decrease in Progesterone due to luteolysis
-Release of negative feedback of Progesterone at level of hypothalamus -> increases GnRH -> increases FSH, LH
-Increasing Estrogen produced by developing dominant follicle
-+ feedback of Estrogen on GnRH surge center at level of hypothalamus
-Large release of GnRH triggers release of LH
What is the hormonal profile of the follicular phase?
-Declining Progesterone (regression of previous CL)
-Increasing Estrogen (growing follicles)
-Increased FSH (recruits next wave of follicles)
-Surge release of LH (low Progesterone & High Estrogen)
What grows and regresses constantly throughout the Estrous cycle?
-Follicles
What are the 4 follicular dynamics?
-Recruitment (Emergence)
-Selection
-Dominance
-Atresia
What is the recruitment follicular dynamic?
-Phase of follicular development where cohort of small antral follicles begin to grow & secrete Estrogen
What is the selection follicular dynamic?
-Follicles selected from previously recruited follicles
-Either become atretic (die) or progress further
-Follicles that progress continue to secrete increasing amounts of Estrogen
What is the dominance follicular dynamic?
-Characterized by one (monotocous spp) or more (polytocous spp) large preovulatory follicles
-Follicles produce large amount of Estrogen & Inhibin
-These follicles undergo ovulation
What is the atresia follicular dynamic?
-Antral follicles in which antrum disappears (they die)
-Most follicles that are recruited undergo atresia (very few advance to ovulation)
-Atresia occurs continuously throughout folliculogenesis
What does monotocous mean?
-Single follicle is selected
What does polytocous mean?
-Multiple follicles are selected
Do all follicles ovulate?
-No
-> 99% of follicles never ovulate; they undergo atresia
-Majority of a follicle’s life is spent in the prenatal stages
The first follicular wave occurs how?
-Either as Progesterone is rising or during peak Progesterone secretion
-Follicles selected during the 1st follicular wave will become atretic
In cows with 3 follicular waves, when does the second wave occur?
-Occurs during peak Progesterone secretion
-Follicles selected during 2nd follicular wave will become atretic
When is the third follicular wave?
-Initiated before luteolysis & results in dominant follicle that will ovulate
-Only those follicles in the growing phase during luteolysis will become eligible for ovulation
What are the hormone levels in the recruitment follicular dynamics?
-High FSH
-Low LH
-No Inhibin
-No Estrogen
What are the hormone levels in the selection follicular dynamics?
-Low FSH
-Moderate LH
-Low Inhibin
-Low to moderate Estrogen
What are the hormone levels in the dominance follicular dynamics?
-Low FSH
-High LH
-High Inhibin
-High Estrogen
On a cellular level, how does follicle produce Estrogen?
2-cell, 2-gonadotropin model
-LH binds Theca cells causing synthesis of enzymes that convert Cholesterol to Testosterone
-Testosterone from Theca cells travels to Granulosa cells -> when FSH binds to causes synthesis of enzymes that convert Testosterone to Estrogen
-Estrogen leaches into capillaries & becomes systemic
-Systemic Estrogen has effects on brain of increased mating posture, pronation, & physical activity & on repro. tract of increased blood flow, edema, secretion of mucus, etc.
How does oogenesis begin?
With the development of primordial germ cells in the embryo
What is oogenesis process simplified?
-Begins w/ development of primordial germ cells in embryo
-Primordial germ cells divide mitotically into oogonia
-Oogonia divide into primary oocytes that enter 1st meiotic prophase. At end of meiotic prophase, nuclear material is arrested (called dictyate, form of nuclear hibernation)
How does the 1st meiotic division take place in oogenesis?
-At puberty, female begins to cycle & ovulate
-LH surge allows meiotic arrest to be lifted & 1st meiotic division takes place
What does the 1st meiotic division result in?
-Results in formation of secondary oocyte that possesses 1st polar body
What is contained in the 1st polar body?
-1/2 genetic material that will be discarded
When is the ootid formed in oogenesis?
-Around the time of ovulation, 2nd polar body is voided & ootid is formed
When does fertilization occur in oogenesis?
-Slightly before or slightly after the second meiotic division
What happens at fertilization during oogenesis?
-Sperm delivers the other 1/2 of genetic material & zygote formed
-At this point, zygote contains male & female pronucleus
-When pronuclei fuse, early embryo development begins
When is it an embryo in oogenesis?
-When pronuclei fuse
