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How long is the typical menstrual cycle?
By which hormones is the menstrual cycle controlled?
- Follicle stimulating hormone (FSH)
- Luteinising hormone (LH)
From where is FSH secreted and what becomes of it?
- The pituitary gland
- The FSH travels in the blood stream, stimulating the follicle containing the egg to develop and mature
Other than follicle maturation, what is the function of FSH?
It causes the follicle cells to secrete oestrogen
What effects does oestrogen have?
- It binds to oestrogen receptors inside the cells of the endometrium
- This activates transcription within cells lining the wall of the uterus, causing it to repair and thicken
What happens to the hormone levels between days 1 and 10 of the menstrual cycle?
- Oestrogen levels rise slowly
- Oestrogen inhibits the production of FSH
- This is an example of negative feedback
What happens to the hormone levels between days 10 and 14 of the menstrual cycle?
There is a rapid rise in the levels of oestrogen causing positive feedback
What happens to the hormone levels between days 12 and 14 of the menstrual cycle?
There is a surge in levels of FSH and LH
What effects does the surge in LH levels have?
It causes ovulation to occur
What functions, other than ovulation, does LH have?
It causes the transformation of empty follicle cells into a corpus luteum which begins to produce progesterone and oestrogen
What happens to the hormone levels between days 15 and 21?
There is a rise in progesterone levels, peaking at day 21
What effects does progesterone have?
- It binds to specific receptor proteins on the cell membrane of endometrium cells which respond by maintaining a thick lining
- It inhibits the release of FSH and LH by the pituitary gland, another example of negative feedback
What happens if the egg is not fertilised?
- The corpus luteum degenerates and so progesterone is no longer produced
- This fall in progesterone levels causes the constriction of blood vessels in the uterus and the onset of menstruation at the end of the 28 day cycle