In order to understand premenstrual syndrome (PMS), it's important
to understand the menstrual cycle and the related hormone functions.
The menstrual cycle can be divided into
two phases, the follicular phase and luteal phase. The follicular
phase is comprised of the two weeks leading up to ovulation;
the luteal phase follows ovulation and continues until the
onset of menstruation.
Hormone-producing organs are called endocrine
organs. For reproduction, women use primarily three of
these organs: the ovaries, the pituitary gland, and the hypothalamus.
The pituitary gland and the ovaries produce four
hormones that constantly change in concentrations in order
to facilitate fertility: follicle
stimulating hormones (FSH), estrogen
hormone (LH), and progesterone
(P). Meanwhile, the hypothalamus, releasing GnRh, acts as
a conductor, telling signaling to the pituitary and thus the
ovaries when to begin and end production of these hormones.
As hormones travel in tiny, potent quantities through the
blood, they interact with receptor sites that coordinate functions
of the endocrine organs. This constant dance of hormones orchestrates
our fertility-a dance that changes throughout the month and
throughout our lives.
Your cycle begins with the onset of menstruation,
also called the follicular phase. The hypothalamus, in response
to the dramatic drop in estrogen
and progesterone levels from the previous
cycle, sends a message (via the hormone GnRh) to the pituitary
gland for it to release a new batch of follicle
stimulating hormones (FSH) to the ovaries. FSH stimulates
the ovaries to produce estrogen and mature of a small group
of follicles, one that will eventually spur an egg. (follicles
mature into eggs) After about 12 days, the production of estrogen
reaches a critical peak in the body - a signal that ovulation
is ready to occur. However, this does not happen on its own.
The hypothalamus is once again alerted and releases more GnRh
to the pituitary gland. The pituitary gland now releases a
different hormone, the luteinizing
hormone (LH) to the ovaries. The luteinizing hormone is
the trigger that will spur an explosion that releases the
egg from the dominant follicle that has been maturing for
the past 10 days. Ovulation occurs.
Directly following ovulation, the ruptured
follicle from which the egg was released reconnects and becomes
the corpus luteum. In preparation for fertilization, it produces
estrogen and even greater amounts of progesterone to create
an extra lining in the uterus. After about 12 days, if no
fertilization occurs, the corpus luteum dies and estrogen
and progesterone levels plunge. This causes the lining to
be expelled and menstruation to begin.
(continue to Potential
causes of PMS)