Menstruation

File photo Menstruation is the result of a complex series of hormonal events that causes the growth, demise, and the eventual sloughing off of the uterine lining and discharge through the vagina.

Ultimately, the menstrual cycle is a reflection of cyclic changes in secretion of steroid hormones (estrogen and progesterone) from the ovary. The ovarian cycle in women and other female primates is coordinated by a series of chemical signals between the brain, pituitary, and ovary.

Monthly menstruation is a sign of regular ovulation, and cycles that are prolonged or not regular suggest that ovarian function is disrupted. Not only does the hypothalamic-pituitary-ovarian (HPO) axis need to function normally for regular cycles, but pathology of other endocrine organs such as the thyroid and adrenal can also result in menstrual cycle disturbances.

The environment within the body (internal milieu) is under tight homeostatic regulation and, in the absence of genetic defects or disease, is kept exceedingly constant. It is this internal homeostatic regulation that allows us to live in a widely fluctuating external environment with relative ease.

However, there are environmental factors that can negatively impact reproduction, the foremost of these being availability of food. Reduced energy availability (nutritional stress) is thought to be the main factor in menstrual irregularity.

During times when food is limited, physiological functions not necessary for immediate survival, such as growth and reproduction, are put on hold until energy is again readily available.

Along with nutritional stress, psychological and physical stress may also influence reproductive cycles. In times of social stress, such as war, there may be menstrual cycle disturbances in 50% of sexually mature women.

How Is the Brain Involved in Reproduction

At the transition (puberty) between childhood and adulthood, the initial signal that activates the reproductive system is thought to originate in the brain. It is not clear what event actually initiates the process, but it is the increased secretion of gonadotropin-releasing hormone (GnRH) from a few thousand neurons in the hypothalamus that begins the process of sexual maturation.

GnRH is a small peptide (10 amino acids in length) produced in neurons and released from the base of the brain in pulses into a set of specialized vessels, the pituitary portal system, and travels a very short distance to the pituitary gland. These pulses of GnRH occur at about hourly intervals during the first half of the menstrual cycle and cause the release of LH and FSH from the pituitary.

Abnormal Menstrual Cycles

Regular menstrual cycles in young women reflect cyclic ovarian activity and generally are associated with a healthy lifestyle.

Thus the cause for the change in cyclic function should be determined by a health care professional as soon as possible.

To communicate effectively with your peers and students regarding menstrual cycles, you should know and understand normal and abnormal menstrual function and the terminology describing that function.

Although there is no complete agreement on the strict definition of all of the terms describing abnormal menstrual cycles, the list below is a reasonable approximation of these definitions.

These words describing menstrual function are used widely in the scientific literature, but you should assume that the average lay person will probably not be aware of the meaning of these words. Therefore, to avoid misunderstanding and confusion, you should define what you mean when you use these terms in discussion of menstrual problems.

1.   Eumenorrhea (Regular)

This refers to menstrual cycles that occur regularly at intervals of 25 – 38 days. These cycle lengths are generally observed in sexually mature women except during pregnancy and during the pubertal and the perimenopausal (around the time of menopause; this can be several years before the actual cessation of menstrual function) transitions when menstrual cycles are more variable.

2.   Oligomenorrhea (Irregular)

This term refers to infrequent menses or menstrual cycles ath occur inconsistently at intervals of 39 – 90 days, typically with only a few periods a year.

3.   Amenorrhea (Acyclic)

This is when menstrual cycles occur at intervals of greater than 90 days or when there is the complete absence of menstruation. There are two types of amenorrhea that are defined based on whether the woman has experienced previous menstrual cycles.

4.   Primary Amenorrhea

This is when a young woman has not experienced menarche by age 15. In other words, a girl has primary amenorrhea if she has not had her first period by the age of 15.

5.   Secondary Amenorrhea

This is the absence of a menstrual period for six consecutive times or motnhs after menarche has occurred. It is estimated that as high as 5% of the adult women in the population experience secondary amenorrhea sometime in their reproductive life.

There are a number of adjectives to describe the causes of amenorrhea sucha as dietary, emotional, jogger’s, postpartum, and lactational (nursing), but these will be avoided for the most part. However, the term used by clinicians to describe amenorrhea caused by exercise or stress is functional hypothalamic amenorrhea (FHA) and is used widely in the clinical and scientific literature.