Menstrual Cycle

1. Follicular phase 2. Luteal Stage

FSH is the dominant hormone because the oestrogen produced by the developing follicle inhibits LH production

1. Increased frequency of GnRH pulses 2. Increased gonadotrope sensitivity 3. When oestrogen reaches threshold its effect on LH secretion changes from inhibitory to stimulatory.

1. It triggers the oocyte to undergo meiosis II 2. Ovulation - LH activates PG's (PGE and PGF) in the Graafian follicle which activates enzymes which breaks down the wall of the Graafian follicle

Apporoximately at day 14, 9 hours after the LH peak, 32-36 hours after the start.

LH - GnRH pulse decrease to 1-4 per day. LH is sensitive to GnRH and stimulates progesterone release by corpus luteum.

It prepares the endometrium for receiving the conceptus. It stimulates secretion from the endometrial gland.

1. Glycogen 2. Lipids 3. Acid Phosphatases

It continues to secrete sex hormoness for 9 days after which levels drop and by day 12 if no fertilisation has occured the corpus luteum will degenerate and stop producing progesterone and oestrogen which leads to shedding of the endometrium and menstruation.

Cholesterol is delivered to the theca interna which converts them into androgens which are then converted to oestradiol by the granulosa cells.

Oestrogen is cholesterol derived so easily passes through membranes and it binds to receptors on the nucleus where it promotes the transcription of RNA which leads to protein synthesis.

The stratum functionalis of the endometrium shrinks which contricts and twist the spiral arteries thus reducing the blood flow resulting in necrosis. there is a final relaxation of the arteries which washes the stratum functionalis away in patches.