Understanding The Menstrual Cycle

The menstrual cycle is not a subject for the ladies alone to have knowledge of. It is important for both men and women to understand all about it. An understanding of the menstrual cycle will help the woman appreciate and adapt better to this life-long phenomenon. Meanwhile, it will also help the man to know how best to relate with the female during these special moments.

Menstrual cycle is characterised by the presence of bleeding from the vagina when there is no fertilisation. The cycle is initiated by changes in the steroids (estrogen and progesterone) produced by the ovaries. These steroids are controlled by the pituitary gland and hypothalamus.

Some Terms To Learn

Women are expected to have an average of about 400 menstrual cycles in their life time. This occurs in the period between menarche and menopause. For those who may be hearing these terms for the first time, let’s define briefly some terms that relate to the menstrual cycle.

  • Menarche: refers to the very first menstruation a girl experiences. The average age for menarche is 12 years.
  • Menopause: refers to the period when a woman stops having menstrual cycles. Average age for menopause is 45 years.
  • Polymenorrhea: means having cycles with interval of 21 days or less. This results in a woman having more than one menstrual period in a month.
  • Oligomenorrhea: means infrequent light menstrual periods with interval exceeding 35 days. This results in a woman having some months in which there is no menstruation.
  • Amenorrhea: means complete absence of menstrual periods in a woman of reproductive age. Amenorrhea is however normal during pregnancy, few months after delivery, breastfeeding mothers, before puberty and after menaupause. Anything outside these is abnormal and you should seek medical help.
  • Dysmenorrhea: this  means painful menstruation characterised by abdominal cramps.
  • Hypomenorrhea: means abnormally light menstrual periods. There is very little blood flow.
  • Menorrhagia: refers to excessive flow of heavy and prolonged menstrual periods.
  • Metrorrhagia: refers to bleeding at irregular times outside your normal expected interval of menstrual cycle.

What is the normal length? 

This is determined by the rate and quality of egg follicles that grow and develop in the ovaries. Cycle lengths are usually unstable and varies in the early teenage years and 5 years before menopause. The normal average menstrual cycle length is however, 28 days. If your cycle lengths are between 21 – 35 days, that’s also considered as normal. Very slim and obese women tend to have longer cycle lengths.

The normal duration of your menstrual flow should be between 2 – 6 days. Meanwhile, the normal average volume of blood flow during your period should be between 30ml – 35ml. Any bleeding greater than 80ml is considered as excessive.

Other factors that can affect the length of your cycle and blood flow can include

How Your Body Controls Menstruation

Let us now take a look at how your body controls the entire process of menstruation. It is fairly simple to understand. What you should keep at the back of your mind is that the menstrual cycle is all about hormones and steroids playing tricks on your ovaries and uterus.



The normal menstrual cycle is controlled by the interactions between the your hypothalamus, pituitary gland, ovaries and endometrium (inner lining of the uterus). These produce the hormones and steroids that control the menstrual cycle in this order:

  1. Hypothalamus:  This secretes Gonadotropin Releasing Hormone (GnRH) which acts on the pituitary gland to release it’s own hormones.
  2. Pituitary gland: It secretes two hormones –  Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH). They all act on the ovaries to release its own androgens (steroids).
  3. Ovaries: The ovaries produce two steroids – estrogen and progesterone. Estrogen is vital for ovulation while progesterone acts on the endometrium to prepare it for implantation or menstruation if fertilisation does not occur.
  4. Endometrium: This is the inner lining of the uterus and has a layer of tissue enriched with blood vessels called functionalis. This is what you shed off during menstruation. It is actually this shedding off of the functionalis that results in the bleeding you see when menstruating.

What Actually Goes in a Menstrual Cycle

The interrelationship between the parameters mentioned above is what brings about the 3 different phases of the menstrual cycle. They are :

  1. The Follicular or proliferative phase
  2. The ovulatory phase
  3. The luteal or secretory  phase

The follicular phase lasts for a period between 7 – 21 days. This phase is the beginning of the menstrual cycle. Low circulating estrogen and progesterone levels is what triggers the hypothalamus and pituitary gland to secrete FSH and LH through a negative feedback mechanism. FSH levels increase and stimulates the maturation of egg follicles in the ovaries. These matured egg follicles cause the ovaries to further secrete more of estrogen and progesterone for the next phase of the menstrual cycle.

During the ovulatory phase of the menstrual cycle, which lasts for between 2 – 6 days, there is high levels of FSH and estrogen. They are responsible for the formation of matured egg follicles which are now ready to be released as ovum. At this stage, there is a surge of LH levels which begin to initiate the release of the egg from the ovaries into the fallopian tubes.  Rising progesterone levels then acts on the endometrium resulting in endometrial growth of the functionalis. Immediately after ovulation, estrogen levels begin to decline as well as FSH and LH levels.

In the luteal phase, LH stimulates the ovarian follicles remaining after ovulation to transform into corpus luteum which is responsible for the release of more progesterone. This results in a thickened and enlarged endometrium ready for the incoming ovum. If there is no fertilisation, the corpus luteum regresses, progesterone levels decline and the unfertilised ovum, together with the endometrium (functionalis) is shed off as menstruation. Luteal phase is fairly constant in duration of about 14 days, after which the cycle commences again.



  • Wikipedia : Disorders of the menstrual cycle
  • A. K. Ghosh et al, (2008), “women’s health – menstruation ” Mayo Clinic Internal Medicine Review, 8th edition, (pg 1059).
  • S. Campbell, A. Monga (2006), ” The Normal Menstrual cycle ” Gynaecology by Ten Teachers, 18th edition, (pg 32-40).

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