Lecture 22: Female cyclicity (Exam 2) Flashcards
Define estrous
The length of the estrous cycle (in bovine its 21 D)
Define estrus
Period of sexual receptivity (heat)
Define Estrous cycle
Consists of a series of predictable reproductive events beginning @ estrus. Provides females w/ repeated opportunities to copulate & become pregnant
Define Anestrus
Not cycling
Define Estrual
Used to identify a condition related to estrus
Define parturition
Giving birth
Define Uterine involution
Acquisition of norm uterine size & fxn (gross & histologic have different time frames)
What are the types of estrous cycles
- Polyestrus
- Seasonally polyestrus
- Monoestrus
Describe a polyestrus cycle
- Have a uniform distribution of estrous cycles throughout the entire year
- Cattle, Swine & rodents
Describe seasonally polyestrus
- Have “clusters” of estrous cycles that occur only during a certain season of the year
- Short day breeders: they cycle as the day length is decreasing (fall); sheep, goats, deer, & elk
- Long-day breeders: they cycles as the day length increases (spring); mares
Describe monoestrus
- Have only one cycle per year
- Dogs, wolves, foxes, & bears
- Domestic dogs typically have 3 estrous cycles per 2 years but are classified monoestrus
Label the types of estrous cycles
What are the two major phases of the estrous cycle
- Follicular phase
- Luteal phase
Describe the follicular phase
- Primary ovarian structure is a large follicle(s)
- Primary/dominant hormone = estradiol secreted by follicles
- Period from CL regression to ovulation
Describe the luteal phase
- Primary ovarian structure is the corpus luteum (CL)
- The primary/dominant hormone = progesterone secreted by the CLs
- Period from ovulation to CL regression
- Follicles continue to grow/regress but do not produce high quantities of estradiol
- 1 CL per egg
- Twice as long as the follicular phase
What is the sequence of the estrous cycle
Follicular phase -> ovulation -> luteal phase -> follicular phase
Describe the levels of estrogen (E2) & progesterone (p4) during the estrous cycle
- Begins to peak right before ovulation
- Drops back down to the luteal phase
- P4 goes down during the follicular phase w/ luteolysis then goes back up in the luteal phase
What are the 4 stages of the estrous cycle
- Proestrus
- Estrus
- Metestrus
- Diestrus
Describe proestrus
- Begins whne progesterone declines as a result of luteolysis & ends @ onset of estrus
- 2 - 5 D depending on species
- Has major endocrine transition (P4 -> E2)
- Pituitary gonadotropins, FSH & LH, are the primary hormones responsible for the transition
- Antral follicles mature for ovulation & the tract prepares for estrus & mating
Which two stages are part of the follicular phase
- Proestrus
- Estrus
Describe the estrus stage
- Peak of estradiol secretion by the dominant follicle
- Female sexual receptivity
- Visible behavioral symptoms so often the most recognizable stage
- Duration varies
Which stages are part of the luteal phase
- Metestrus
- Diestrus
Describe Metestrus
- CL formation (luteinization)
- Beginning of progesterone secretion
- Transition from estradiol dominance to progesterone dominance
Describe diestrus
- Sustained secretion of high levels of progesterone from mature CLs
- Longest stage of the estrous cycle (2/3 of the cycle)
- Ends w/ luteolysis (destruction of the CL)
label the image
Label the following
What are the exceptions to the estrous cycle
- The bitch
- The queen
Describe the bitch estrous cycle
- Anestrus - 5 M; not ovulation
- Proestrus - 9 D; start bleeding
- Estrus - 9 D; start ovulating
- Diestrus - 2 M
Describe the hormones during the bitch’s estrous cycle
- FSH - Med to high (in anestrus or spayed); estrogen starts negatively feedback w/ FSH during proestrus
- Estrogen - follicles grow & peak during proestrus then drops after estrus
- LH - Has negative feedback w/ estrogen during proestrus so it drops
- Ovulate & fertilize days after FSH drop
- Progesterone increases during diestrus
Label the following:
Describe the queens estrous cycle
- Are induced ovulators
- Proestrus
- Estrus
- Postestrus - Interestrus period in queen not mated (no ovulation); about 7 - 10 days
- Only have diestrus if they were stimulated or had natural ovulation (about the same length as gestation)
- Anestrus
Describe the hormones during a queen in estrus w/ no mate
- Estrogen is low w/ spikes
- P4 stays low
Describe the hormones during a queen in estrus w/ a mate
- Still have spikes
- High P4 during pregnancy
- Dont have P4 during lactation so they can reproduce during lactation period
Label the following:
Describe anestrus
- “Without cyclicity”
- Females that do not exhibit reg estrous cycles
What are the causes of anestrus
- Pregnancy
- Lactation (not in cats)
- Presence of offspring
- Season (Photoperiod)
- Stress
- Pathology
What is true anestrus
- Insufficient hormonal stimulus
- Due to poor nutrition, stress, pathology, high performing athletes b/c they don’t have the energy to put into estrous
What is apparent anestrus
- Failure to detect estrus
- Failure to recognize that a female is pregnant
- Like a mare is at the bottom of the pack and doesn’t want to show estrus
What is gestational anestrus
- Norm condition brought about by inhibition of GnRH by progesterone
- Should ALWAYs be on dx list for anestrus
- Owners sometimes have no clue about exposure & may even lie
What is lactational anestrus
- Not seen in cats
- Not in mares, alpaca/llamas, & dairy cows
- Lasts for variable amounts of time
- Cyclicity is completely suppressed during lactation in the sow
- Cyclicity can be delayed for as long as 60 D (suppression of LH)
what can influence the duration of lactational anestrus
- Suckling sessions (threshold not continuum)
- 2 or less suckling sessions per day promotes return to cyclicity
- 3 or more causes post partum anestrus
- Dairy cows typically do not display lactational anestrus b/c the calf is removed
- Beef cows typically have @ least a 60 D lactational anestrus
How does the presence of offspring affect cyclicity
- When calves are weaned suddenly from cows w/ intact mammary nerves the LH pulse freq & amplitude increases (cow returns to cyclicity)
- Same thing happened when the nerves were cut
- Suckling cannot be totally responsible for suppressing LH in the postpartum cow
- Presence of the calf has some effect
What does seasonal anestrus enables animals to do
- Carry dev fetus during favorable time
- Give birth during and advantageous time for new born
T/F: Seasonal anestrus can be modified by photoperiod to come back to cyclicity
True
What is the possible role of kisspeptin neurons in the regulation of cyclicity in long & short day breeders
- Long: More light = less melatonin = start cycling
- Long day breeders: Increased kiss-10 causes increased GnRH which in turn causes increased FSH & LH
- Short day breeders: Decreased Kiss-10 causes decreased GnRH which causes decreased FSH & LH
How does stress induce anestrus
- Neg energy balance
- When an animal is starved the repro system is the first to shut down
- Females consuming low quantities of E or protein often have sustained period
- In lactating animals the lack of nutrition will prolong lactational anestrus (esp true for first time/young moms)
What is folliculogenesis
The process whereby immature follicles dev into more advanced follicles & become candidates for ovulation
T/F: Females make new eggs over time
False females are born w/ a few hundred thousand primordial follicles
What are the primary ovarian structures
- Primary follicles
- Secondary follices
- Antral (tertiary) follicle(s)
- CL
- Corpora albicans (a white scar(
What governs the follicular phase
- Hypothalamus
- Anterior pituitary
- Ovary through secretion of estradiol in the absence of progestrone
What are the four significant events of the follicular phase
- Gonadotropin (FSH & LH) released from the anterior love of the pituitary
- Follicular preparation (growth) for ovulation
- Sexual receptivity
- Ovulation (LH)
What is the dominant hormone? What does it do?
- Dominant hormone: Estrogen
- Causes changes in the reproductive tract
- Behavioral changes
- Controls the onset of preovulatory LH surge
What does the tonic center of the hypothalamus do
- Releases small amplitude pulses of GnRH that stimulate release of FSH and LH from the anterior pituitary
- These cause the growth & dev of follicles on the ovaries
- The follicles produce estrogen
What does the surge center of the hypothalamus do
- Responds in a positive feedback to the increasing levels of estrogen in the absence of progesterons
- The positive feedback of estrogen on the hypothalamus causes release of a LARGE quantity of GnRH
- This large dump of GnRH causes release of LH (LH surge)
- Results in ovulation
- The surge center is turned on once estrogen reaches a threshold level
Label the following steps leading to the preovulatory LH surge:
T/F: Estradiol exerts a positive feedback on the hypothalamus that drives the surge release of GnRH
True
Describe the hormonal profile of the follicular phase
- Declining progesterone (regression of the previous CL)
- Increasing estrogen (growing follicles)
- Increased FSH (recruits next wave of follicles)
- Surge release of LH (low progesterone & high estrogen)
T/F: Follicles grow & regress constantly throughout the estrous cycle
True
Label the following
Describe the difference btw/ the types of follicles & oocyte
- Follicle is the sack that the oocyte is in
- The secondary is bigger than the primary in both the follicle & oocyte
Label the following
What is recruitment (emergence)
Phase of follicular dev in which a cohort o small antral follicles begin to grow & secrete estrogen
What are the phases of follicular dev
- Recruitment (emergence)
- Selection
- Dominance
- Atresia
Describe the recruitment
Phase of follicular dev in which a cohort of small antral follicles begin to grow (emerge) & secrete estrogen
Describe selection
- Follicles selected from prev recruited follicles
- Either become atretic (die) or progress further
- Follicles that progress continue to secrete increasing amounts of estrogen
Describe dominance
- Characterized by on (monotoccous sp) or more (polytocous sp) large preovulatory follicles
- Follicles produce a large amt of estrogen & inhibin
- The follicles undergo ovulation & the others die off
Describe atresia
- Antral follicles in when the antrum disappears (they die)
- Most follicles that are recruited undergo atresia & very few advance to ovulation
- Atresia occurs cont. throughout folliculogenesis
Define monotocous
Single follicle is selected
Define polytocous
multi follicles are selected
Where is the majority of a follicle’s life spent
in the preantral stages
What % of follicles never ovulate (they undergo atresia)
> 99%
What are the hormones during recruitment
- High FSH
- Low LH
- No Inhibin
- No estrogen
What are the hormones during selection
- Low FSH
- Moderate LH
- Low inhibin
- Low to mod estrogen
What are the hormones during dominance
- Low FSH
- High LH
- High inhibin
- High estrogen
What is the process of the 2-cell 2 gonadotropin model
- When LH binds to theca cells it causes synthesis of enzymes that convert cholesterol to testosterone
- When FSH binds to the granulosa cells it causes synthesis of enzymes that convert testosterone to estrogen
- The estrogen leaches into the capillaries & become systemic
- The systemic estrogen has effects on the brain of increased mating posture, phonation, & physical activity
How does system estrogen have an effect on the repro tract
- Increased BF
- Edema of tissues
- Secretion of mucus
- Increased leukocytes
- Increased smooth muscle motility
- Growth of uterine glands
What is the steps of oogenesis
- Begins w/ the dev of primordial germ cells in the embryo
- Primoridal cells divid e mitotically into oogonia
- Oogonia divide into primary oocytes that enter the first meiotic prophase
- At the end of the meiotic prophase the nuclear material is arrest (called dictyate) to form nuclear hibernation
What are the steps of oogenesis after puberty
- The female begins to cycle & ovulate
- The LH surge allows the meiotic arrest to be lifted & the first meiotic division takes place
- This results in the formation of a secondary oocyte that possesses the first polar body (contains 1/2 of the genetic material that will be discarded. 4N to 2N)
- Around the time of ovulation the second polar (2N to 1N) is voided & the ootid is formed
- At fertilization the sperm delivers the other 1/2 of the genetic material & a zygote is formed
- The zygote contains a male & female pronucleus when the pronucleii fuse early embryo dev begins
