Menstrual cycle (menstruation)

  • The menstrual cycle is the regular natural change that occurs in the female reproductive system (specifically the uterus and ovaries) that makes pregnancy possible.
  • It refers to the series of events that occur in the ovaries of sexually mature and non-pregnant females and culminate in menses.
  • The menstrual cycle is approximately 28 days long.
  • The cycle is required for the production of oocytes.
  •  This cycle is also for the preparation of the uterus for pregnancy.
  • The beginning of this cycle marks the onset of puberty in human females.
  • It begins at the age of 12-14 years and goes till the age of 50-55 years.
  • During each menstrual cycle, an egg matures and is positioned to meet a sperm cell in the fallopian tube.
  • If the egg is not fertilized, it is then washed out.
  • Up to 80% of women report having some symptoms during the one to two weeks prior to menstruation.
  • Common symptoms include acne, tender breasts, bloating, feeling tired, irritability and mood changes.
  • The complete menstrual cycle involves four different phases. They are:

1. Follicular phase:

  • It is the period prior to ovulation.
  • It begins when the hypothalamus produces a releasing factor.
  • The releasing factor stimulates the anterior lobe of the pituitary gland to release follicle stimulating hormone (FSH).
  • It is transported through the blood stream and causes a group of ovarian cells, called a follicle to form the egg.
  • Simultaneously, FSH promotes the production of the hormone oestrogen, which is released in the blood stream.
  • Oestrogen, in turn, stimulates the lining of the uterus to thicken and the pituitary gland to produce luteinizing hormone (LH).
  • This hormone then causes the maturation of the eggs.

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  • As the egg matures, the follicle moves towards the surface of the ovary, ruptures and releases the ripe eggs. This is called ovulation.
  • It happens during middle of the menstrual cycle.
  • During ovulation, the small finger-like projections (fimbriae) draw the egg from the ovary into the fallopian tube.
  • The egg remains in the fallopian tube for about 4 days and can be fertilized during this time.
  • The egg or zygote (if it is fertilized) then moves through the fallopian tube to the uterus, which is now thick and lined with mucus.

3.Luteal phase:

  • The luteal phase is the period between the ovulation and the onset of menstruation.
  • It lasts for 14 days, i.e. from 15th to 28th day of the cycle.
  • During this period, the ruptured follicle left on the surface of the ovary, develops into a golden coloured new structure, called the corpus luteum.
  • It secrets a hormone progesterone, that further prepares the uterus for the anticipated pregnancy.
  • The uterine lining becomes thicker and almost ready to nourish and protect the fertilized egg.
  • The secretion of progesterone and its level in blood is controlled by luteinizing hormone.

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  • If the egg was fertilized in the fallopian tube, the resulting embryo attaches to the lining of the uterus.
  • If the egg was not fertilized, it will not attach to the lining.
  • In this case, corpus luteum stops producing progesterone and the soft tissues of uterine lining are cast off.
  • These tissues along with the unfertilized egg are discharged in the last stage of the cycle.
  • This is called menstruation.
  • In other words, menstruation or menses is a period of mild bleeding (haemorrhage) during which the uterine epithelium is sloughed and expelled from the uterus.
  • It usually occurs every 28 days.
  • The bleeding lasts for about 4-5 days. At this time, the level of oestrogen and progesterone is very low in the blood.
  • Following the menstruation the cycle begins again.

Criteria for cycle phase determination using hormone events and... |  Download Table

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Menstrual cycle (menstruation)