6. 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.
11. What control
follicular growth?
?????
Gonadotropin
independent
Ovulation
4 8 12 16 20 24 28
0
Oestradiol
Menstruation
As each follicle grows, it produces
increasing amt of Estradiol
12. The follicle is the fundamental element of the ovary
LH
Androgens are converted
(aromatized) to estradiol by
granulosa cells
Androgens
FSH Oestradiol
Inhibin
14. FSH As the follicle grow, FSH level fall due to the
–ve feedback mechanism
Estradiol
0 4 8 12 16 20 24 28
15. Why is only one
selected & become
dominant ?
Many follicles at
the start of the
cycle
Ovulation
4 8 12 16 20 24 28
0
Menstruation
16. Hypothalamus
Increasing GnRH
–ve
feedback - Pituitary
mechanism
Inhibin
suppress
Oestradiol
↓FSH
FSH
+
Small folicle
Ovary Large folicle
very dependent independent on
on FSH FSH
Growth factor
estradiol
X Dominant
+ + follicle
17. FSH secretion suppressed
FSH
Estradiol
Dominant
follicle (s)
can survive
Insufficient FSH to
keep smaller follicle
going to become
atretic
0 4 8 12 16 20 24 28
18. What causes ovulation ?
Oestradiol
What effects
does it have ?
What causes
LH surge ?
0 4 8 12 16 20 24 28
19. Hypothalamus
For most of the
cycle negative
feedback GnRH
mechanism -
operates
Pituitary
↓ LH & FSH
LH
Inhibited by
FSH
estradiol
Estradiol
Ovary
20. Hypothalamus
↑GnRH
But, with high
level of estradiol GnRH
maintained for + ↑Sensitivity
to GnRH
long enough
Pituitary
+
LH surge
Estradiol
Ovary
21. How does the LH
surge affects the
follicle ?
About 36 h between
LH surge & oocyte
release…..
22. Oocyte
Loosening of the
cumulus cells
Enzyme induction in
the follicle wall
Oocyte
23. Transformation of ruptured follicle into
corpus luteum
Mature follicle become
Corpus luteum
Steroid secretion
changes
Progesterone +
Estradiol
24. What maintains
the CL ?
Follicular phase Luteal phase
Estradiol domination Progesterone domination
Why does the CL
degenerates at
the end of the
cycle ?
0 4 8 12 16 20 24 28
Ovulation
25. What maintains
the CL ?
Hypothalamus
~8 h between LH
pulses
GnRH
Pituitary
LH very low
levels
CL
CL very sensitive
Progesterone + to LH
E2
26. What maintains
the CL ?
Hypothalamus
-
GnRH
Steroid negative
feedback keeps Pituitary
LH & FSH level
relatively low -
LH
(low levels in
CL + luteal phase)
Progesterone +
E2
CL very sensitive
Reproductive to LH
tract etc
27. Towards the end Hypothalamus
of the cycle, the
sensitivity to LH
reduces GnRH
Pituitary
The low level of
LH are
insufficient to
keeps the CL LH
going
CL degenerates
Progesterone +
E2
28. Hypothalamus
GnRH
As CL
degenerates Pituitary
steroid negative
feedback reduces
↑ FSH + LH
Progesterone +of folicles
A new wave
stimulated by rising FSH & LH
E2
29.
30.
31.
32. Other changes in the cycle
1. Outer muscles layer the
myometrium
3. Inner glandular layer mucusa
the endometrium
33. Uterine changes in menstrual cycle
Endometrial depth
Estradiol cause an ↑ in More secretion from the
thickness gland, hence the term
(the proliferative phase) secretory phase
0 4 8 12 16 20 24 28
Opt time for
Ovulation implantation
34. 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
35. 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