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ZIMSEC O Level Combined Science Notes: The menstrual cycle

  • The reproductive cycle in females is called the menstrual/estrus cycle
  • It has an average of 28 days
  • It varies from individual to individual but it follows a set pattern
  • The cycle is regulated by hormones produced by the pituitary gland and ¬†ovaries
  • The cycle can be tracked using various charts and diagrams
Simplified menstrual cycle chart

Simplified menstrual cycle chart. Image credit

  • Menstruation occurs from days 1-5
  • From days 5 to 10 the uterus lining starts to thicken
  • Ovulation occurs midway within the cycle usually from days 10 to 14
  • During this time the ovum (egg) is released.
  • It is the most fertile period of the cycle
  • If copulation/sexual intercourse takes place fertilization can take place
  • On Days 14 to 21 the uterus lining remains intact and ready to receive a zygote
  • That is if fertilization occur
  • On days 22 to 28 the uterus walls continue to thicken and may break at the end of this period
  • On days 1 to 5 the uterus lining breaks down if fertilisation has not taken place
  • The blood and lining are expelled from the body
  • This process is known as menstruation

To access more topics go to the Combined Science Notes page