Menstrual cycle Flashcards Preview

REPRO > Menstrual cycle > Flashcards

Flashcards in Menstrual cycle Deck (26):

Regulation of sex steroid production

GnRH from hypothalamus - cyclic release in adulthood
stimulates release of LH & FSH from anterior pituitary, stimulate ovary
ovaries produce steroids (estradiol from granulosa; progesterone from luteal)


Theca cells

produce androstenedione


Granulosa cells

produce estrogens (mostly estradiol)


Postovulatory changes to cells

Theca and granulosa cells become luteal cells
--> produce estrogen and progesterone


Primary follicles over life

undergo apoptosis from birth onwards
2 mil primordial follicles at birth
400k remain at puberty
average woman will ovulate 500 times


Ovarian component f menstraul cycle

maturing an oocyte and its ovulation
follicular phase is variable, luteal is fixed: 12-14 d


Endometrial component of the menstrual cycle

Proliferative phase
secretory phase
atretic phase


Ovarian cycle

requires LH/FSH input from ant pituitary
LH and FSH promote development of androgen secreting cells surrounding the follicle --> proliferation
high levels of circulating androgens --> ovulation of mature oocyte
following ovulation, androgen profile changes dramatically to inhibit subsequent ovulation


Early ovarian follicular phase

Primary follicles respond to increasing FSH, develops theca/granulosa cells
LH: promotes theca cells to increase androstenedione production
FSH: promotes granulosa cells to increase estradiol production
Estradiol promotes local sensitivity in each developing primary follicle
- granulosa cell proliferation
- estrogen receptor expression, insertion
- FSH receptor expression, insertion
- LH receptor expression, insertion on granulosa cells


Late ovarian follicular phase

first follicle to develop LH receptors on granulosa cells = dominant follicle
Dominant follicle responds to LH with estrogen surge in plasma
Estrogen surge: positive feedback effect on ant pituitary --> increased LH production
LH SPIKE prior to ovulation
Dominant follicle inhibits sister follicle development (paracrine)


Steroid production during ovarian follicular phase

initiated by LH binding to theca cell
FSH binding to granulosa cell: conversion of androgens to estrogen by aromatase
LH receptors on dominant follicle greatly enhance estrogen production


Ovulatory phase

LH surge: due to estrogens from dominant follicle --> critical for ovulation
Requires 2 days of elevated estrogen
LH surge triggers ovulation by:
- neutralized action of oocyte maturation inhibitor
- increased enzyme prostaglandin endoperoxidase synthase
--> PG, thromboxane, leukotriene production to break down ovary wall
Contraction of follicular wall


Ovarian luteal phase

In response to elevated LH, granulosa/theca cells form the corpus luteum
Luteal cells respond to LH by producing estrogen, progesterone
If oocyte is not fertilized, luteal cells degenerate after 12 days
--> decreased progesterone as a result
--> will stimulate ant pituitary to start next cycle


Proliferative phase of endometrium

cells lining uterus divide in response to estradiol from granulosa cells, forming layers of glands and blood vessels


Secretory phase of endometrium

after ovulation, cell division halts
progesterone augments blood supply and initiates secretion of acid mucin


Atretic phase

in absence of fertilized oocyte, progesterone decreases --> loss of uterine lining
produces bleeding for 2-4 days
next cycle begins on day 1 of bleeding and marked by an increase in FSH


Regulation of ovulation during follicular phase

Onset of cycle: loss of estrogen/progesterone from luteal cells --> drive increasing FSH levels
follicular development, increasing estrogen
estrogen levels during follicular phase are LOW and feedback to inhibit GnRH/LH release
inhibin from granulosa cells inhibit release of FSH


Regulation during luteal phase

estrogen drops, progesterone rises
Progesterone inhibits GnRH, FSH, LH
prevents new follicular formation/ovulation
when oocyte not fertilized, corpus luteum atrophies - progesterone levels drop, removes inhibition
cycle begins again with increasing FSH


Early follicular phase overview

low hormone activity
releases negative feedback at hypothalamus and ant pituitary (due to low progesterone)
FSH rises - folliculogenesis, estradiol release at ovary


Mid follicular phase overview

Estradiol levels increase:
- follicles grow
- endometrium proliferates


Late follicular phase overview

Dominant follicle "seleted" - first to develop LH receptor
estradiol surge from dominant follicle in response to LH
Endometrium thickening
cervical mucous changes
dominant follicle suppresses growth of other follicles


Overview of early luteal phase

estrogen surge --> positive feedback on ant pituitary --> LH surge
- first meiotic division
- ovulation
- corpus luteum: produces progesterone, neg feedback on LH, FSH


Overview of mid luteal phase

Progesterone levels rise
organization of endometrium


Late luteal phase overview

w/o fertilization, CL degenerates after 12 days
estradiol/progesterone levels drop
endometrium sloughs - menses


Histology of endometrium during follicular phase

Proliferative phase (growth)
endometrial stroma thickens, glands elongate
no crowding


Histology of endometrium during luteal phase

Secretory (stabilization)
estrogen/progesterone mediated
endometrial stroma becomes loose and edematous
blood vessels become thickened and twisted
endometrial glands tortuous
>50% ratio glands to stroma