Hello, my name is Diane Duffy.
I'm a Professor and a Vice Chair for Research in
the Department of Physiological Sciences at
Eastern Virginia Medical School in Norfolk, Virginia.
In the first part of my talk,
I described the female reproductive tract and the ovary
and the structural transformation of the ovulatory follicle.
In this second part of my talk,
I will describe the endocrine and paracrine control of ovulation.
Ovulation involves many interrelated events which must be carefully controlled in
time and especially around the follicle if ovulation is to be successful.
These events are controlled by a primary endocrine signal, luteinizing hormone,
abbreviated LH, and a large number of locally produced hormones called paracrine factors.
Just to review the basic endocrine control of the menstrual cycle,
antral follicle growth occurs in response to follicle stimulating hormone or FSH.
The fastest growing follicle will become the preovulatory follicle.
This is the follicle that will go on to ovulate.
High levels of estrogen produced by growing follicles
initiates the release of the surge of luteinizing hormone, abbreviated LH.
LH acts at cells of the follicle to stimulate the changes we've already discussed,
which are changes needed for ovulation.
Endocrine control of ovulation is regulated by
both negative and positive feedback at the hypothalamus and the anterior pituitary.
Generally, steroid hormones, estrogen and progesterone,
have a negative feedback effect at the hypothalamus and anterior pituitary,
meaning that these steroid hormones reduce the amount of FSH and LH released.
In the follicular phase as FSH is stimulating the growth of many follicles,
these growing follicles produce more and more estrogen.
Estrogen feedback reduces the amount of FSH produced to regulate follicle growth.
Declining levels of FSH allow a single,
large responsive follicle to grow large enough to ovulate.
As this growing follicle approaches ovulatory size,
the very high amount of estrogen produced has a positive feedback effect,
resulting in a rapid increase in FSH and LH release.
The increase in serum LH level is substantial and is called the LH surge.
The surge of FSH is also released,
but it is of lower magnitude than the surge of LH.
We believe that the surge of LH provides
the important physiologically meaningful stimulus for ovulation.