The menstrual cycle and fertilisationPrint
If you are doing the higher exam papers you need to know the roles of oestrogen and progesterone (see previous page) and also two other hormones: follicle stimulating hormone (FSH) and luteinising hormone (LH).
FSH and LH are both produced by the pituitary gland [pituitary gland: An endocrine gland that is located just below the centre of the brain. It releases a number of important hormones.] in the brain and are transported in the blood.
Low progesterone levels allow FSH levels to stimulate an egg (in a follicle in the ovary) to be matured. This encourages the production of oestrogen which repairs the uterus wall and stimulates a surge of LH. This triggers ovulation [ovulation: Release of a mature egg from an ovary.] .
After the egg is released from the follicle, it develops into the corpus luteum [corpus luteum: The remains of the follicle in a mammalian ovary after it has released an ovum (egg) into the fallopian tube. The corpus luteum secretes hormones involved in the menstrual cycle.] . This produces progesterone which maintains the lining of the uterus and so stops menstruation. Progesterone inhibits FSH and LH and so remains high during pregnancy.
This animation shows how the levels of FSH and LH change during the menstrual cycle.
The menstrual cycle is an example of a negative feedback mechanism. This is when a substance is produced in our bodies to return a system to normal.
Negative feedback is also seen in the formation of ADH (anti-diuretic hormone) in the kidneys. In this case, ADH is produced when the brain detects too little water and so the kidney reabsorbs more water. The opposite happens when the brain detects too much water.