Endocrinology of the menstrual cycle
Dr. Nelson Soucasaux, Brazilian gynecologist
In my book "Novas Perspectivas em Ginecologia," I have observed
that the complexity of the neuroendocrine, endocrine, biochemical and psychical
phenomena that occur in the female organism at each ovarian and menstrual
cycle is so great that we can even say that it is very difficult to find
two exactly equal menstrual cycles. Even from the exclusive endocrine point
of view, there are lots of possible patterns in the secretion of estrogens
and progesterone - as well as of androgens, which, curiously, are precursors
of the estrogens in the sexual steroids synthesis.
There are also anovulatory cycles, in which there is no progesterone
(except on the minimal basal levels, that have no clinical importance, and
only exist because progesterone synthesis is one of the first stages in
the synthesis of all other sexual steroids, both the gonadal and suprarenal
ones). Even in ovulatory cycles, the interrelations between estrogens and
progesterone levels exhibit great variations from cycle to cycle. Here we
must remember that during the first phase of a typical ovulatory cycle,
there is an increasing production of estrogens by the growing ovarian follicles
- mostly by the dominant follicle, the one that will ovulate. It is only
after ovulation, in the second phase of the cycle, with the luteinization
of the ruptured follicle and formation of the corpus luteum, that this structure
begins to produce adequate levels of progesterone. Together with progesterone,
the corpus luteum also produces estrogens.
Therefore, throughout ovulatory cycles (considered as biphasic), women
produce good levels of estrogens during the two phases of the cycle, while
progesterone is only produced in adequate levels in the second phase. On
the other hand, during anovulatory cycles (considered as monophasic) there
is only a significant production of estrogens (which can be moderate, normal
or even elevated, a fact that can create situations of relative or absolute
hyperestrogenism). At the end of each ovarian cycle (ovulatory or anovulatory),
there is a sudden fall in the hormonal levels, which cause the regression
and necrosis of the endometrium and the consequent menstrual desquamation
of this tissue.
The beginning of menstruation is the most evident external event that
indicates the end of a cycle and the beginning of a new one. For clinical
purposes, of a practical order, it was stipulated in a simplified way to
consider the first day of menstruation as being the first day of the new
cycle that initiates, and this is how we usually proceed in Gynecology.
However, it must be said that, in the intimacy of the complex phenomena
that occur in the ovaries (both in the histologic and endocrine points of
view), it is impossible to determine with precision the end of one cycle
and the beginning of the next one.
All estrogenic and/or estrogenic-progesteronic cyclical actions produce
innumerable cyclic transformations in the female sexual organs (genitals
and breasts), in women's physiology and in other parts of their bodies.
These rhythmically arranged changes can also generate, through the somatopsychic
pathways, psychological alterations. The ovarian cycle is controlled by
the hypothalamus-hypophyseal system by means of feedback mechanisms and,
because of this, it also controls this system. There is a continuous two-way
interaction between both, by extremely intricate mechanisms.
Simplifying too much the subject for didactical purposes, this is what
happens: the hypothalamus (part of the brain which the hypophysis is attached
to), by means of the production of a neurohormone known as Gn-RH (gonadotropin
releasing hormone), controls the hypophyseal release of the gonadotropins,
which are the follicle stimulating hormone (FSH) and the luteinizing hormone
(LH). FSH and LH are the hypophyseal hormones that control the ovarian function,
commanding the processes of follicular maturation, ovulation, formation
of the corpus luteum and synthesis of the sexual steroids. The estrogens
produced in the ovaries under the hypophyseal gonadotropic command cause,
in turn, negative and positive retroactive effects upon the hypothalamic
centres responsible for the Gn-RH production.
There is also some interference in these mechanisms due to prolactin,
another hypophyseal hormone whose main action takes place on the breasts.
The release of prolactin by the hypophysis is also controlled by a hypothalamic
factor formerly known as PIF (prolactin inhibiting factor), presently identified
as the neurohormone dopamine. Furthermore, the hypothalamus is always receiving
influences from other parts of the brain, as the limbic system and the cortex.
The interaction between the psyche and the cerebral cortex demonstrates
how women's emotional problems interfere on the hypothalamus-hypophysis-ovaries
axis, being capable of generating various endocrine disorders, including
many of those that are usually seen in gynecologic practice.
Considering the multiplicity of effects produced by the ovarian hormones
in the female body, the more evidently manifested ones are: 1) the puberal
changes, through which the girl's body acquires the typical features of
the adult woman's body; 2) the innumerable phenomena that occur in the sexual
organs along each cycle - among them, the periodic uterine bleeding which
The text above is an excerpt from my book "Novas Perspectivas
em Ginecologia" ("New Perspectives in Gynecology"). For more
information on the book, see page http://www.nelsonginecologia.med.br/novas.htm
from my Web site www.nelsonginecologia.med.br
©Nelson Soucasaux 1990, 2001
Nelson Soucasaux is a gynecologist especially dedicated to clinical,
preventive and psychosomatic gynecology. Graduated in 1974 by Faculdade
de Medicina da Universidade Federal do Rio de Janeiro, Brazil, he is the
author of several articles published in medical journals and of the books
"Novas Perspectivas em Ginecologia" ("New Perspectives in
Gynecology") and "Os Órgãos Sexuais Femininos: Forma,
Função, Símbolo e Arquétipo" ("The
Female Sexual Organs: Shape, Function, Symbol and Archetype"), published
by Imago Editora, Rio de Janeiro, 1990, 1993.
©2001 Harry Finley. It is illegal
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