The Menstrual Cycle
- Created by: chloe
- Created on: 29-04-13 18:23
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- Menstrual Cycle
- lasts about 28 days but can vary
- cycle is continuous with the one that went before and the one that will follow
- first day of menstruation is considered as 'day 1' of the cycle
- menstruation is the loss of the inner layer of the endometrium accompanied by a small volume of blood
- made up of 2 phases
- follicular
- FSH from anterior pituitary stimulates the development and maturation of Graafian follicle and production of oestrogen by the ovarian tissues
- as the concentration of oestrogen builds up, it brings about repair and proliferation of the endometrium
- eventually the high concentration of oestrogen triggers a surge in production of LH by the anterior pituitary at about day 14
- the surge of LH is the direct cause of ovulation since it makes the blister like wall of the graafian follicle rupture and release the egg
- egg is then moved slowly along the oviduct, during a short period of about 3 to 4 days , fertilisation may occur if the egg meets a sperm
- luteal
- follows ovulation
- LH stimulates the graafian follicle to become the corpus luteum which secretes progesterone and oestrogen
- the rise in progesterone concentration stimulates further development of the endometrium
- it becomes thick, vascular and spongy, ready to accept and nourish an embryo, if fertilisation takes place and the embryo becomes implanted
- combined high levels of oestrogen and progesterone during this luteal phase also trigger an inhibitory efect on the anterior pituitary
- concentrations of FSH and LH drop as a result and no new follicles develop at this time
- lack of LH leads to the degeneration of the corpus luteum by about day 22, this is followed by a rapid drop in progesterone
- by day 28 these ovarian hormones are at such a low level that the endometrium can no longer be maintaines and menstruation begins
- follicular
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