Menstrual cycle

Question 1

Regulation of sex steroid production

Answer 1

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)

Question 2

Theca cells

Answer 2

produce androstenedione

Question 3

Granulosa cells

Answer 3

produce estrogens (mostly estradiol)

Question 4

Postovulatory changes to cells

Answer 4

Theca and granulosa cells become luteal cells

–> produce estrogen and progesterone

Question 5

Primary follicles over life

Answer 5

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

Question 6

Ovarian component f menstraul cycle

Answer 6

maturing an oocyte and its ovulation

follicular phase is variable, luteal is fixed: 12-14 d

Question 7

Endometrial component of the menstrual cycle

Answer 7

Proliferative phase
secretory phase
atretic phase

Question 8

Ovarian cycle

Answer 8

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

Question 9

Early ovarian follicular phase

Answer 9

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

Question 10

Late ovarian follicular phase

Answer 10

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)

Question 11

Steroid production during ovarian follicular phase

Answer 11

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

Question 12

Ovulatory phase

Answer 12

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

Question 13

Ovarian luteal phase

Answer 13

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

Question 14

Proliferative phase of endometrium

Answer 14

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

Question 15

Secretory phase of endometrium

Answer 15

after ovulation, cell division halts

progesterone augments blood supply and initiates secretion of acid mucin

Question 16

Atretic phase

Answer 16

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

Question 17

Regulation of ovulation during follicular phase

Answer 17

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

Question 18

Regulation during luteal phase

Answer 18

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

Question 19

Early follicular phase overview

Answer 19

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

Question 20

Mid follicular phase overview

Answer 20

Estradiol levels increase:

• follicles grow
• endometrium proliferates

Question 21

Late follicular phase overview

Answer 21

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

Question 22

Overview of early luteal phase

Answer 22

estrogen surge –> positive feedback on ant pituitary –> LH surge

• first meiotic division
• ovulation
• corpus luteum: produces progesterone, neg feedback on LH, FSH

Question 23

Overview of mid luteal phase

Answer 23

Progesterone levels rise

organization of endometrium

Question 24

Late luteal phase overview

Answer 24

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

Question 25

Histology of endometrium during follicular phase

Answer 25

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

Question 26

Histology of endometrium during luteal phase

Answer 26

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