Follicular Physiology/ Ovulation/ Luteolyis Flashcards
What are the 4 major events of the follicular phase ?
Rising level of gonadotropin from AP
Follicular growth/ prep for ovulation
Sexual receptivity
Ovulation
What is the dominant hormone released during the follicular phase?
Estrogen
How id proestrual follicular development initiated?
Leuteolysis leads to a decrease in progesterone
GnRH levels increase
FSH and LH levels increase
—> follicular development
Follicles produce what hormones that feedback to the anterior pituitary?
Inhibin — negative feedback on FSH
Estradiol — positive feedback to surge center for release of GnRH, negative feedback at AP for FSH
This will lead to an LH surge —> ovulation
What are the steps from the ovarian follicular pool that leads to an ovulatory follicle?
Recruitment (stimulated by FSH and LH)
Selection —> some of the recruited follicles will become atretic or progress further
Dominance — selected follicles that do not undergo atresia produce large quantities of E2
Ovulation
What are the hormone levels of FSH, LH, inhibin and E2 during follicular recruitment?
FSH - high
LH - low
Inhibin — none
E2 — none
What are the hormone levels of FSH, LH, inhibin and E2 during follicular selection?
FSH - low
LH- moderate
Inhibin — low
E2- low
What are the hormone levels of FSH, LH, inhibin and E2 during follicular dominance ?
FSH - low
LH - high
Inhibin - high
E2- high
Where does estrogen come from?
2-cell, 2-gonadotropin model
Theca interna cell turns cholesterol into testosterone
Granulosa cell uses testosterone to make estradiol
LH binds to ________ cells resulting int he production of _________ hormone
Theca interna, testosterone
FSH binds to ___________ cells resulting in production of __________ hormone
Granulosa cells, E2
The preovulatory LH surge stimulates an increase in what hormones?
Increased PGE2
increased PGF2a
Progesterone
An increase in PGF2a causes what?
Release of lysosomal enzymes —> follicle wall weakens
Increased contraction of ovarian smooth muscle —> increased follicular pressure
Ovulation
The primordial germ cells have how many chromosomes ?
2N (diploid)
Primary oocytes have how many chromosomes?
2N (diploid) —> 4N with arrest at first meiotic prophase (arrested here until LH surge )
Secondary oocyte has now many pairs of chromosomes?
2N with 1st polar body (following first meiotic divisions)
At the time of ovulation how many chromosome pairs are in the oocyte?
1N with 2 polar bodies
What is an induced ovulator?
Requires stimulation of the vagina and/or cervix for ovulation to occur
Sensory neurons within the vagina and at the cervix sense copulation and relay this signal to the surge center —> GnRH release —>LH release —> ovulation
What is the duration of the LH surge in most speices?
24hrs
Except in mares where it is elevated form 3-5days
T/F: All animal except the cow ovulate during estrus, except the cow
True
Eg bitch ovulates 2-3days after LH surge
What occurs to the follicle following ovulation
Collapses
Fills with blood — corpus hemorrhagicum
Most species ovulate a secondary oocyte, except __________ who will ovulate a primary oocyte
Canids
What two phases of the estrous cycle occur during the luteal phase?
Metestrus and diestrus
What are the 3 main events of the luteal phase?
Lutenization of follicular cells to luteal cells
Growth/development of CL —>progesterone production
Luteolysis
What is the process of lutenization?
Transformation of the theca interna cells into small luteal cells and granulosa cells into large luteal cells —> producing progesterone
What other hormones besides progesterone does the CL produce?
Oxytocin
Relaxin
What are the physiological effects of progesterone?
Hypothalamus — neg feedback, decrease GnRH
Anterior pituitary — neg feedback
Uterus — positive influence on uterine glands to secrete “uterine milk” for potential concepts, reduces myometrial tone
Mammary glands — prior to parturition causes final alveolar development
What is luteolysis?
Disintegration of the CL
—> dramatic drop in progesterone (1-3days)
What is the luteolytic agent in domestic animals and where does it come form?
PGF2a
Uterine endometrium (except in dog)
How does PGF2a get from the uterus to the ovaries in ruminant vs mare vs sow?
Ruminant — local countercurrent exchange from ipsilateral uterine vein to ovarian artery in ruminants
Mare — systemic
Sow— combination of the both
When do oxytocin receptors appear in the endometrium?
10-14days of increasing P4
CL contains large amounts of oxytocin
Oxytocin release stimulates a pulse of PGF release —> oxytocin release (positive feedback)
