follicular phase Flashcards
when does the folicular phase begin and end
Initiated immediately after luteolysis annd ends after ovulation`
follicular phase is slipt into two segments, what are they
proestrus and estrus
what initiates the follicular phase endocrinologically
initiated immediately after luteolysis which means the negative feedback on the hypothalamus of progesterone is released (corpous lutem decreases P4 production) and thus increases GnRH. (High FSH and LH production increases)
what is the dominant hormone in the follicular phase
Estrogen
decribe key elements of the proestrus phase in the follicular phase
Elevated gonadotropin from the anterior pituitary
The surge center stimulates ovulation by increasing the LH release when the threshold of GnRH is released (promoted by estrogen in the blood).
Low progesterone is crucial as when both estrogen and progesterone is high the surge center reacts differently
AKA - low progesterone, high LH and GnRH
The surge center release of LH is how many times greater than the tonic centers pules of LH
10
The release of gonadotropin is controlled by…
hypothalamic GnRH
release of GnRH is mainly controlled by which hormone…
Estrogen
describe key element of the estrus period in the follicular phase
Follicular growth and preparation for ovulation
remeber the dynamic of the antral follicle
Antral follicle size responds to the ________ hormone levels;
LH and FSH
what is atresia and how many undergo it
degradation of an antral follicle
90% of follicles will undergo irreversible atresia
what are the three steps in follicular dynamics
recruitment
selection
dominance
describe recuritment in follicuar dynamics, what is achives and the hormone requirments
Segment of which the follicles grow and produce estrogen
High FSH + low LH + no inhibin + no estradiol
what are the two stages in the follicular dynamics recruitment phase, and what occurs
Initial recruitment phase - the growth of finite follicles in the follicle pool that terminates with atresia (this is your pool for recruitment)
Cyclic recruitment phase - begins after puberty when FSH levels are high, occurs during each cycle
describe selection in follicuar dynamics, what is achives and the hormone requirments
Follicles which have not undergone atresia are selected. Theses follicles begin to grow dominant or they undergo atresia
Low FSH + moderate LH + low inhibin
describe dominance in follicuar dynamics, what is achives and the hormone requirments
As follicle enlarge and become dominate they increase production of estrogen as well as hormone inhibin (hormone which decreases FSH secretion in anterior pituitary)
Low FSH + high LH + high inhibin
how is selection in the follicuar dynamics diffrent in monestrus and polyestrus animals
Monotocous species will only select one follicle to develop dominance
Polytocous species will have multiple dominant follicles and they are classified by having a large inhibitory effect on antral follicles, this is thought to be the effect of inhibition and reduced blood supply to some follicles. This will likely result in atresia.
describe the hormonal changes occuring in recruitment during follicular dynamics
During recruitment, FSH increases thus prompting antral follicle growth. FSH pays a more important role in LH in antral follicle growth.
describe the hormonal changes occuring in selection during follicular dynamics
As the follicles enter the selection phase, inhibin and estradiol are produced by the follicles and inhibit FSH secretion from the anterior lobe into the pituitary. Thus the relative role of LH and FSH shifts. FSH is at its lowest secretion and LH is increasing at the time of selection.
describe the hormonal changes occuring in dominance during follicular dynamics
The largest follicle produces more estrogen. This prompts the preovulatory center to release a surge of LH. In addition FSH secretion remains low because inhibin and estradiol are secreted in high levels by the dominant follicle. This drop in FSH is believed to cause other antral follicles to undergo atresia.
what is the end goal of the 2 cell 2 gonadotrophin model
Estrogen synthesis
give a breif description of the 2 cell, 2 gonadotropin model
- LH binds to receptors on the theca interna
- this causes cholesterol to be converted into testosterone
- testosterne in converted into estrogen in the granulosa cell with the binding of FSH
- estrogen then enters the blood which stimulate the surge center to release mass LH to prepare for ovulation
list the effects of estrogen
Mucosal of the epithelial tract responds to estrogen. The caudal vagina increases thickness in response.
Increased blood flow
Genital swelling
Change in tissue electrical conductivity
Leukocytosis
Increased mucosal secretion
Initiation of uterine gland growth
Elevated myometrial tone.
What is ovulation
Process which involves the purposeful destruction of follicular tissue
Ovulation is caused by three main things
Elevated blood flow
Breakdown of connective tissue
Ovarian contractions
what is oogenesis
process of which produces a mature ovum
what is the significance of follicular fluid OTHER then pressure
Follicular fluid is found to have angiogenic factors which increase blood flow which aid in the follicular pressure.
after the LH surge caused by the estrogen threshold in the GnRH what two hormones are produced by the ovary and released locally
prostaglandin F2a (causes contraction of the myoid and ruptures lysosome)
prostaglandin E2 (aids the follicles transition into a corpus luteum)
There are four phases of oocyte development, name them,
mitotic division (prenatal), nuclear arrest (dictyotene), cytoplasmic growth and resumption of meiosis
describe mitotic division (prenatal) during oocyte devlopment
Primary oocyte enters the first mitotic prophase
describe the nuclear arrest during oocyte development
Oocyte is then arrested and dormant until stimulated by gonadotropin after puberty. This is so that the DNA remains inactive so that it cannot be damaged.
describe the cytoplasmic growth during oocyte development
Neonatal females begin to accumulate larger volumes of cytoplasm and develop a translucent band surrounding it, this is the zona pellucida (second follicular phase).
Oocyte growth is primarily mediated by what?
granulosa cells through the junctional comlpex between the follicular cells
describe the resumption of meiosis during oocyte development
Once in the dominant phase the oocyte is ready to undergo meiosis when the LH discharge occurs.
The preovulatory discharge of gonadotropins is needed to release oocyte from the inhibitors, freeing from its nuclear arrest by removing inhibitors.
Once meiosis begins the oocyte migrates to the periphery and flatterns against the plasma membrane. The meiotic division mostly occurs before ovulation, producing the second polar body.
Histamine and prostaglandin E2 (PGE2) do what to aid in rupture of the dominant follicule
increase blood flow which affects the theca interna as it swells due to the increased vascular flow
Before ovulation the theca interna produce progesterone instead of testosterone. why?
The progesterone then stimulates the synthesis of collagenase which breaks down collagen (major component of connective tissue).
Connective tissue makes up the tunica albuginea (outer layer of ovary) thus progesterone begins to break down the tunica albuginea.
contrations in the what increase pressur on the protruding follicle?
myoid
PGF(2a) has what effect on the granulose cells
The lysosomes in the granulosa cells ruptured under the influence of PGF2a which released their enzymes which degrade the connective tissue further.
PGE(2) effects the ruptured follicle how
PGE2 directs the follicle to reorganize by activating a substrate called plasminogen which dissolves the coagulum of the corpus hemorrhagicum.
what are the two types of ovulation
Spontaneous - ovulate frequently without the precursor of copulation
Reflex (induced) - requires stimulation of the vagina and/or cervix
