The menstrual cycle is a recurring process which takes around 28 days.
During the process, the lining of the uterus is prepared for pregnancy. If implantation of the fertilised egg into the uterus lining does not happen, the lining is then shed. This is known as menstruation.
Several hormones are involved in the menstrual cycle of a woman:
|FSH (follicle stimulating hormone)||Pituitary gland||Causes an egg to mature in an ovary; stimulates the ovaries to release oestrogen|
|Oestrogen||Ovaries||Stops FSH being produced (so that only one egg matures in a cycle); repairs, thickens and maintains the uterus lining; stimulates the pituitary gland to release LH|
|LH (luteinising hormone)||Pituitary gland||Triggers ovulation (the release of a mature egg)|
|Progesterone||Ovaries||Maintains the lining of the uterus during the middle part of the menstrual cycle and during pregnancy|
If a woman becomes pregnant, the placenta produces progesterone. This maintains the lining of the uterus during pregnancy and means that menstruation does not happen.
The menstrual cycle lasts for approximately 28 days. Graphs can be used to follow changes to the hormones during this process.
Describe the relationship between the different hormones during the 28 days.
Days 1 to 12 - oestrogen gradually increases and peaks approximately on the 12th day. Progesterone, LH and FSH stay approximately at the same levels and begin to increase slightly from around day 12.
FSH and LH patterns are very similar and peak during ovulation at approximately 14 days during this cycle. They drop sharply on day 15 and stay constant until day 28.
Oestrogen drops during days 13 and 14, and progesterone continues to gradually increase until about day 21, when it slowly beings to decrease again. Oestrogen mirrors this shape and also has a second lower peak at about day 21.