Menstruation is the regular occurrence of menstrual periods in females about every 4 weeks. Start of menstruation is called Menarche. Failure to menstruate is called “Delayed Menarche” or “Primary Amenorrhea”. Absence of periods is Amenorrhea (Secondary Amenorrhea when periods occurred, and then disappeared). Cessation of menstruation is Menopause, which is preceded by a time called Perimenopause. Menstrual symptoms include menstrual pain, absent periods (amenorrhea), irregular periods, abnormal vaginal bleeding, and many other symptoms. Menstruation-related disorders include Pre-Menstrual Syndrome, Pre-Menstrual Dysphoric Disorder (PMDD), Anovulation, Fertility Disorders, Female Infertility, and many others.

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What is menstruation?

Menstruation is the cyclical loss (known as sloughing) of the inner layer of the uterus (called the endometrium) which occurs as a result of a complex interaction between hormones in the brain (hypothalamus and pituitary gland) and the ovaries.

The normal menstrual cycle is approximately 28 days and starts on the first day of menses (also known as the period).  During the first 14 days of this cycle (known as the follicular phase), the hypothalamus releases a hormone called gonadotropin-releasing hormone (GnRH), which stimulates the release of  two hormones (follicle-stimulating hormone (FSH) and luteinizing hormone (LH)) from the anterior pituitary gland. These two hormones have multiple effects, one of which is to act on the ovaries to stimulate the production of oestrogen. Oestrogen causes the endometrium to thicken.

In the middle of this cycle (day 14), the ovary is stimulated to release an egg in a process called ovulation. This marks the end of the follicular phase and the beginning of a phase called the luteal phase. The main hormone responsible during this phase is progesterone.  Progesterone is released from the part of the ovary from which the egg came (now called the corpus luteum) and makes the uterus more receptive to implantation of an embryo, which is necessary for pregnancy.

If implantation fails to occur after 12 to 15 days, the corpus luteum degenerates and stops producing hormones. This loss of hormones leads to changes in the uterus, which ultimately leads to sloughing of the endometrium and menses.

Source: Queensland Health1

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Menstruation is commonly called a period, and is what adolescent girls and women of child-bearing age usually experience as a flow of blood from the vagina.

It is caused by a build-up of blood on the lining of the womb (uterus), in response to hormones. Periods usually last between 3-7 days, with the blood flow usually starting heavy and getting lighter during this time.

Most girls or women get their period once a month, but anywhere between every 3 and 6 weeks is normal.

Source: Queensland Government2

Introduction: Menstruation

What causes periods?

Periods are triggered by hormones that send a message to the uterus to prepare for a possible pregnancy. These hormones make the lining of the uterus thick so that if an egg is fertilised by male sperm, it can implant safely in the uterus wall.

If the egg isn't fertilised and no pregnancy occurs, the uterus sheds the thick lining. The blood that leaves the vagina during the period is due to the uterus lining coming away.

This process continues to happen monthly until you reach your late 40s to early 50s. When your hormones decrease and your periods stop, this is called menopause.

Watch an animated movie about the reproductive cycle.

Source: Queensland Government3

Introduction: Menstruation

What is menstruation?

Menstruation is a woman’s monthly bleeding, often called your “period.” When you menstruate, your body discards the monthly buildup of the lining of your uterus (womb). Menstrual blood and tissue flow from your uterus through the small opening in your cervix and pass out of your body through your vagina.

During the monthly menstrual cycle, the uterus lining builds up to prepare for pregnancy. If you do not get pregnant, estrogen and progesterone hormone levels begin falling. Very low levels of estrogen and progesterone tell your body to begin menstruation.

Source: OWH (DHHS)4

Introduction: Menstruation

What is the menstrual cycle?

The menstrual cycle is the monthly hormonal cycle a female’s body goes through to prepare for pregnancy. Your menstrual cycle is counted from the first day of your period up to the first day of your next period. Your hormone levels (estrogen and progesterone) usually change throughout the menstrual cycle and can cause menstrual symptoms.

Source: OWH (DHHS)5

Introduction: Menstruation

Menstruation, or period, is normal vaginal bleeding that occurs as part of a woman's monthly cycle. Every month, your body prepares for pregnancy. If no pregnancy occurs, the uterus, or womb, sheds its lining. The menstrual blood is partly blood and partly tissue from inside the uterus. It passes out of the body through the vagina.

Periods usually start between age 11 and 14 and continue until menopause at about age 51. They usually last from three to five days. Besides bleeding from the vagina, you may have

Source: MedLinePlus (NIH)6

Introduction: Menstruation

What is the menstrual cycle?

When periods (menstruations) come regularly, this is called the menstrual cycle. Having regular menstrual cycles is a sign that important parts of your body are working normally. The menstrual cycle provides important body chemicals, called hormones, to keep you healthy. It also prepares your body for pregnancy each month. A cycle is counted from the first day of 1 period to the first day of the next period. The average menstrual cycle is 28 days long. Cycles can range anywhere from 21 to 35 days in adults and from 21 to 45 days in young teens.

The rise and fall of levels of hormones during the month control the menstrual cycle.

Source: OWH (DHHS)7

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Menstrual Cycle: The period from onset of one menstrual bleeding (Menstruation) to the next in an ovulating woman or female primate. The menstrual cycle is regulated by endocrine interactions of the Hypothalamus; the Pituitary Gland; the ovaries; and the genital tract. The menstrual cycle is divided by Ovulation into two phases. Based on the endocrine status of the Ovary, there is a Follicular Phase and a Luteal Phase. Based on the response in the Endometrium, the menstrual cycle is divided into a proliferative and a secretory phase.8

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Menstruation: The normal physiologic discharge through the vagina of blood and mucosal tissues from the nonpregnant uterus.9


Types may include:10

Types of Menstruation:

  • Heavier Menses

Categories for Menstruation

Category of Menstruation:

  • Endocrine System Signs and Symptoms

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  1. Source: Queensland Health: HealthCondition/ condition/ 21/ 145/ 4/ amenorrhoea
  2. Source: Queensland Government: health/ staying-healthy/ men-women/ women/ menstruation
  3. ibid.
  4. Source: OWH (DHHS): menstrual-cycle/ your-menstrual-cycle
  5. ibid.
  6. Source: MedLinePlus (NIH): menstruation.html
  7. Source: OWH (DHHS): publications/ our-publications/ fact-sheet/ menstruation.html
  8. Source: MeSH (U.S. National Library of Medicine)
  9. Source: NCI Thesaurus
  10. ibid.
  11. ibid.
  12. [from HPO]
  13. Source: GTR (NCBI/NIH): gtr/ conditions/ CN183090/ 
  14. Source: NHS Choices UK: conditions/ stopped-or-missed-periods/ 
  15. Source: OWH (DHHS): menstrual-cycle/ period-problems
  16. Source: Queensland Health: HealthCondition/ condition/ 21/ 145/ 4/ amenorrhoea
  17. Source: NICHD (NIH): health/ topics/ amenorrhea/ Pages/ default.aspx

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Note: This site is for informational purposes only and is not medical advice. See your doctor or other qualified medical professional for all your medical needs.