Physio of the Estrous Cycle Flashcards
Who is involved in the endocrine regulation of the estrous cycle?
Hypothalamus: GnRH
Hypophysis: FSH and LH
Ovaries: estradiol, progesterone, inhibin
Uterus: Prostaglandin PF2a
What role does inhibin play in the estrous cycle?
Prevents the development of multiple follicles during ovulation. Only one follicle should ovulate.
What is the follicle producing from the primary stage to the Graffian stage?
Estradiol
What is the follicle producing after the Graffian stage (CH and CL)?
Progesterone
Where in the ovaries are follicles found?
Cortex
If ovulation without fertilization occurs, the uterus produces _____ to lyse the corpus luteum and begin another cycle.
Prostaglandin PGF2a
What are the committed follicles?
Follicles from the resting pool that are activated to begin growing
When is development of the follicle gonadotropin (FSH and LH) independent?
Up to the formation of the antrum.
- Independent: primordial, primary, secondary
- Responsive: preantral, antral
Gonadotropin dependent stages of follicle development
Antral, Graffian, up until ovulation
At what stage is the follicle most susceptible to atresia?
Preantral to early antral transition, during formation of the theca cell layer
Features of the corpus hemorrhagicum
Immediately after ovulation
Antrum collapses
Low progesterone levels
*will see bloody discharge in cows
Features of the corpus luteum
Theca interna and granulosa cells proliferate and differentiate into small and large luteal cells.
Progesterone levels increase
Large luteal cells also secrete oxytocin and relaxin
Area of the brain responsible for regular pulses of GnRH
Tonic GnRH Center of the hypothalamus.
*affected by internal and external (melatonin) signals
Area of the brain responsible for releasing bursts of GnRH to initiate ovulation.
Surge Center of the hypothalamus
- female brain only!
- w/out sufficient GnRH burst, surge of LH is not released and ovulation doesn’t occur
Effects of estrogen during ovulation
Thickening vaginal mucosa Mucus secretion Epithelial mitosis (endometrium) Increased secretory and ciliary beat activity Endometrial edema Myometrial activity Estrous behavior
Ovulation is initiated by a surge of ___, and then Theca interna cells begin to produce _______ rather than androstenedione.
LH, progesterone
During ovulation, the corpus luteum secretes ______, which _____endometrial secretion, _____ myometrial activity, and primes the brain to enhance the effects of ______.
During ovulation, the corpus luteum secretes PROGESTERONE, which INCREASES endometrial secretion, REDUCES myometrial activity, and primes the brain to enhance the effects of ESTROGEN.
If fertilization does not occur, the uterine endometrium produces ______, which is released into the ____ ____, enters the ____ ____, and is delivered to the ovary where it causes lysis of the ____ _____.
If fertilization does not occur, the uterine endometrium produces PGF2a, which is released into the UTERINE VEIN, enters the UTERINE ARTERY, and is delivered to the ovary where it causes lysis of the CORPUS LUTEUM.
Luteolysis is _______ in ruminants and _____ in the mare and sow
ipsilateral, systemic
Progesterone from the CL forms a negative feedback loop with the hypothalamus to ensure what?
Continued tonic release of LH from the adenohypophysis to support the CL until PGF2a causes CL regression
Inhibin forms a negative feedback loop with the pituitary to regulate what?
FSH release
Melatonin _____ GnRH release in short day breeders like small ruminants, and _____ GnRH release in long day breeders like horses.
Melatonin INCREASES GnRH release in short day breeders like small ruminants, and DECREASES GnRH release in long day breeders like horses.
Definition of puberty
Age at which the body can produce adequate amounts of GnRH and respond to it.
- acquisition of capability of sexual repro
- production of gametes
- onset of cyclicity in females
Sexual maturity differs from puberty and involves
Body growth and adequate size for pregnancy/delivery/lactation
What’s up with the pulse generator in juveniles?
That boi is dormant
What adipocyte hormone senses ideal body size and maturity, and helps mediate the onset of puberty?
Leptin
For contraception, the most efficient place to regulate GnRH production is…
at the hypothalamus
Human and primate contraception works by…
preventing development of pre-ovulatory follicles
3 phases of the estrous cycle
Follicular/Proliferative
Luteal
Quiescent
Polyestrous animal. Not season specific.
Cow
Monoestrous animal. Not season specific.
Dog
Animals that are seasonally polyestrous
Horse
Sheep
This phase of the ovarian cycle is estrogen dominated, includes proestrus and estrus, and involves development of follicles
Follicular/Proliferative
This phase of the ovarian cycle takes place from ovulation to CL regression and is progesterone dominated.
Luteal/Secretory
