Understanding
the mechanisms of the normal menstrual cycle lays the foundation for
understanding the path physiology of anovulatory bleeding and its treatment.
Menstrual cycle resulting in ovulation
is the result of a complex interaction between the various organs. A normal
menstrual cycle occurs every 21-35 days with menstruation for 2-7 days. The
average blood loss is 35-150 ml, with usually no more than 2 heavy days.
During the normal menstrual cycle, the
first day corresponds to the first day of menses. The menstrual phase usually
lasts 4 days and involves disintegration and soughing of the functionalis layer
of the endometrium. The Prolifeeration (Follicular) phase extends from the day
5 to day 14 of the typical cycle. It is marked by endometrial proliferation
bought on by estrogen stimulation.
The
estrogen is produced by the developing ovarian follicles under the influence of
FSH. The phase ends as estrogen produced by the developing ovarian follicles
under the influence of FSH.
The phase ends as estrogen production
peaks, triggering the FSH and LH surge. Repture of the ovarian follicle follows
with release of the ovum (Ovulation). The Secretary (Luteal) phase is marked by
the production of progesterone and less potent estrogen by the corpus luteum.
It extends from the day 15 to day 28 of the typical cycle. The functionalis
layer of the endometrium increases in thickness and stroma becomes oedematous.
If fertilization does not occur the estrogen and progesterone feedback to the
hypothalamus, and FSH & LH production falls. The spiral arteries become
coiled and have decreased flow. At the end of the cycle, they alternately
contract and relax, causing a breakdown of the functionalis layer and menses to
begin.
Pathway of action of hormones for normal
menstrual function. A menstrual cycle of fewer than 21 days or more 35 days or
a menstrual flow of fewer than two days
or more than seven days is considered abnormal.