The menstrual cycle

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:

HormoneWhere producedRole
FSH (follicle stimulating hormone)Pituitary glandCauses an egg to mature in an ovary; stimulates the ovaries to release oestrogen
OestrogenOvaries 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 glandTriggers ovulation (the release of a mature egg)
ProgesteroneOvariesMaintains 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 interactions of hormones - Higher

The menstrual cycle lasts for approximately 28 days. Graphs can be used to follow changes to the hormones during this process.

A diagram representing the menstrual cycle and hormone levels

Question

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.

Greg Foot describes the interaction of FSH, LS, oestrogen and progesterone in the menstrual cycle