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CH 8 cyclicity the follicular phase - Coggle Diagram
CH 8 cyclicity the follicular phase
Elevated gonadotropin secretion from the anterior lobe of the pituitary
Follicular phase is governed by the hypothalamus, the anterior lobe of the pituitary and the ovary through secretion of estradiol in the absence of progesterone
Episodic profile pattern - basal GnRH secretion controlled by the
tonic center release small pulses
over days to weeks
GnRH secretion is responsible for stimulating the release of FSH and LH causing growth and development of follicles
Surge center responsible for surges of LH causing ovulation. it responds to high blood conc of estradiol
Secretes basal levels of GnRH until it receives a threshold conc. of estradiol in the absence of progesterone (positive stimulus)
once threshold is reached the preovulatory center is turned on and secretes lg quantities of GnRH that stimulate the anterior lobe to secrete the surge of LH that causes ovulation
Follicular growth and preparation for ovulation
Selection
follicles that have not undergone atresia are selected
Low FSH + moderate LH + low inhibin
Dominance
After luteolysis, follicles of the 2nd or 3rd wave will develop into dominant follicle
Low FSH + High LH pulse frequency + high inhibin
Recruitment
a group of small antral follicles begins to grow and secrete estradiol
high FSH + low LH pulse frequency + low inhibin + low estradiol
Atresia
occurs continuously throughout folliculogenesis
Degeneration of follicles
Sexual receptivity
Copulation is required in the reflex (induced) ovulators
Superovulation
due to abnormally high number of follicles (from higher FSH) that are selected followed by ovulation
Four stages of maturation are : mitotic division of primordial germ cells (prenatal), nuclear arrest (dictyotene), cytoplasmic growth, and resumption of meiosis
hormonally induced ovulation
This requires premature luteolysis
Spontaneous ovulators do not require copulation
ovulation
Elevated blood flow, breakdown of connective tissue, and ovarian contractions
LH surge
theca interna produce progesterone that stimulates the synthesis of collagenase
collagenase breakdown collagen (major part of CT
Prostaglandin E2 and F2 alpha are synthesized and excreted by the ovary
F2 alpha causes lysosomes in the granulosal cells to rupture and release their enzymes
increase in follicular pressure and weakening of follicle wall
Ovulation
E2 helps follicle remodel itself into a CL after ovulation