menstrual cycle
DESCRIPTION
Menstrual cycle in womenTRANSCRIPT
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Menstrual cycle
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0 4 8 12 16 20 24 28
Onset of menstruation
Menstruation
Day 1 Day 1
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0 4 8 12 16 20 24 28
Key events in ovarian cycle
Menstruation
Day 1
Ovulation
Oestradiol
LH
1. Follicular growth
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0 4 8 12 16 20 24 28
LH surge
Menstruation
Day 1 Day 1
Days before Days after
Follicular phase
Luteal phase
Ovulation
LH
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0 4 8 12 16 20 24 28
Key events in ovarian cycle
Menstruation
Day 1
Ovulation
Oestradiol
1. Follicular growth
LH
2. Ovulation
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When does ovulation occur?
The timing of ovulation varies with the length of a woman's menstrual cycle.
In the average 28 day menstrual cycle, the LH surge usually occurs between cycle days 11-13 and ovulation follows about 36-48 hours later, on or close to cycle day 14.
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0 4 8 12 16 20 24 28
Key events in ovarian cycle
Menstruation
Day 1
Ovulation
Oestradiol
1. Follicular growth
LH
2. Ovulation
Oestradiol(& Progesterone)
3. Luteal function
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0 4 8 12 16 20 24 28
Key events in ovarian cycle
Menstruation
Day 1
Ovulation
Oestradiol
1. Follicular growth
LH
2. Ovulation
Oestradiol(& Progesterone)
3. Luteal function
4. Luteal regression
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Zona pellucida
Antrum
OocyteCumulus cells
The follicle is the fundamental element of the ovary
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What control follicular growth?
HypothalamusHypothalamus
PituitaryPituitary
OvaryOvary
GnRH
LHFSH
Estradiol
Reproductive tract
Steroid feedback
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What control follicular growth?
04 8 12 16 20 24 28
MenstruationAs each follicle grows, it produces
increasing amt of Estradiol
?????Gonadotropin independent
Ovulation
Oestradiol
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The follicle is the fundamental element of the ovary
Androgens
LH
OestradiolFSH
Inhibin
Androgens are converted (aromatized) to estradiol by
granulosa cells
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HypothalamusHypothalamus
PituitaryPituitary
OvaryOvary
GnRH
LHFSH
Estradiol
Reproductive tract
Increasing –ve
feedback mechanism
+
-
Increasing amount of estradiol
Inhibin suppress
+↓FSH
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4 8 12 16 20 24 280
Estradiol
FSH As the follicle grow, FSH level fall due to the –ve feedback mechanism
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04 8 12 16 20 24 28
Menstruation
Many follicles at the start of
the cycle
Ovulation
Why is only one selected & become
dominant ?
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HypothalamusHypothalamus
PituitaryPituitary
OvaryOvary
GnRH
FSH
Increasing –ve
feedback mechanism
-
Oestradiol
Inhibin suppress
+↓FSH
Small folicle very
dependent on FSH
Large folicle independent
on FSHGrowth factor
estradiol
+ +X
Dominant follicle
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4 8 12 16 20 24 280
Estradiol
FSH
Dominant follicle (s)
can survive
Insufficient FSH to keep smaller follicle
going to become atretic
FSH secretion suppressed
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0
What causes ovulation ?
4 8 12 16 20 24 28
What causes LH surge ?
Oestradiol
What effects does it have ?
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HypothalamusHypothalamus
PituitaryPituitary
OvaryOvary
GnRH
LHFSH
For most of the cycle negative
feedback mechanism operates
-
Estradiol
↓ LH & FSHInhibited by
estradiol
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HypothalamusHypothalamus
PituitaryPituitary
OvaryOvary
GnRH
But, with high level of estradiol maintained for long enough
+
EstradiolLH surge
↑GnRH
↑Sensitivity to GnRH
+
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How does the LH surge affects the
follicle ?
About 36 h between LH surge & oocyte
release…..
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Oocyte
Enzyme induction in the follicle wall
Loosening of the cumulus cells
Oocyte
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Transformation of ruptured follicle into corpus luteum
Mature follicle become Corpus luteum
Progesterone + Estradiol
Steroid secretion changes
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0
Follicular phase
4 8 12 16 20 24 28
Luteal phaseEstradiol domination Progesterone domination
What maintains the CL ?
Ovulation
Why does the CL degenerates at the end of the
cycle ?
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What maintains the CL ?
HypothalamusHypothalamus
PituitaryPituitary
GnRH
CL
LH very low levels
CL very sensitive to LHProgesterone +
E2
~8 h between LH pulses
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What maintains the CL ?
HypothalamusHypothalamus
PituitaryPituitary
GnRH
CL
LH (low levels in luteal phase)
CL very sensitive to LH
Progesterone + E2
Steroid negative feedback keeps LH & FSH level relatively low
Reproductive tract etc
+
-
-
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HypothalamusHypothalamus
PituitaryPituitary
GnRH
LH
CL degenerates
Progesterone + E2
Towards the end of the cycle, the sensitivity to LH
reduces
The low level of LH are
insufficient to keeps the CL
going
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HypothalamusHypothalamus
PituitaryPituitary
GnRH
↑ FSH + LH
Progesterone + E2
As CL degenerates
steroid negative feedback reduces
A new wave of folicles stimulated by rising FSH &
LH
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Other changes in the cycle
1. Outer muscles layer the myometrium
2. Inner glandular layer mucusa the endometrium
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4 8 12 16 20 24 28
Endometrial depth
Ovulation
Uterine changes in menstrual cycle
Estradiol cause an ↑ in thickness
(the proliferative phase)
More secretion from the gland, hence the term
secretory phase
Opt time for implantation
0
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Time course of menstruation
Onset of menstruation is rapid
Probably, 95% women have a total blood loss of less than 60 ml
This blood loss can represent as a significant loss of iron (leading to anemia)- especially in women on marginal diet
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Menstruation….Why ?
In preparation of pregnancy, the human uterine stromal cells go through complex changes and the stromal cells terminal differentiate
If implantation and pregnancy do not occur, this tissue is lost and the uterus prepares itself again for another possible pregnancy
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0 4 8 12 16 20 24 28
Key events in ovarian cycle
Menstruation
Day 1
Ovulation
Oestradiol
1. Follicular growth
LH
2. Ovulation
Oestradiol(& Progesterone)
3. Luteal function
4. Luteal regression
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Women fertile window
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