The menstrual Cycle

Normal length of mesntrual cycle

28 days +/- 7 days

Best test of pregnancy ?

A high Day 21 progesterone level indicates ovulation and the release of an egg. A low Day 21 progesterone level suggests the cycle was anovulatory (no egg was produced). If no egg is produced, pregnancy cannot be achieved. Additionally, estradiol (E2) is included in the Day 21 testing. Progesterone always peaks 7 days before end of cycle, so always count back 7 days from start of mesntruation and that is the best time to take levels.

Where does fertilisation usually take place ?

Ampulla then fertilized egg travel down fallopian tubes

Timescale of a menstrual cycle

Average length of a menstrual cycle is 28 days but can range from 20-35 days Ovulation usually occurs on day 14. Pre-ovulatory phase for ovary corresponds to ovarian follicular phase and for endometrium corresponds to menstrual and profliferative phase. Post-ovulatory phase for ovary corresponds to ovarian luteal phase and endometrial secretory phase.

Outline the ovarian follicular phase

Before puberty GnRH released constantly - only after puberty that its realeased in a pulsatile manner and that's the signal for menarche to begin.

Ovarian post-ovulatory period - The luteul phase

Corpus luteum produces progesterone which negatively feedbacks onto FSH AND LH production Inhibin produced by granulosa cells also inhibits FSH production Overall effect is a decrease in oestrogen levels and an increase in progesterone.

How does the dominant follicle emerge ?

Decreasing FSH levels result in most developing follicles regressing and eventually dying off. The follicle with the most FSH receptors however can continue to survive and becomes the dominant follicle - the one that will ovulate.

The LH surge

Dominant follicle is releasing oestrogen until a threshold value is reached, at which point pituitary switches to positive feedback loop and rising E2 causes massive release of LH and FSH. This surge then causes rupture of the dominant ovarian follicle and thus ovulation. LH surge occurs approx. two days before ovulation.

What happens in the first ten days ?

FSH primarily responsible for development of OOCYTES to eventually form dominant preovulatory follice.

When is the first day of the cycle generally thought of ?

First day of bleeding

How long do most women bleed for ?

Most bleed for 3-6 days

What is the fixed part of the cycle ?

Post-ovulation, if no fertilisation the endometrium WILL shed after 14 days.

What happens on day 10-14 ?

So granulosa cells develop LH receptors aswell as the FSH receptors they already have. Oestrogen levels also reach a point where they start to negatively feedback onto Ant. pituitary release of FSH. Therefore FSH levels start to decrease.

Endometrial pre-ovulatory period - The proliferative phase

Spiral arteries rise from basal layer to feed functional layer (endometrium). Also oestrogen induces a more alkaline environment in the vagina cervix and uterus.

Areas of the uterus

Top two thirds - functionalis layer - which receives the fertilised egg Lower third - Basalis layer.

Actions of both oestrogen and progesterone on the functionalis layer ?

•Proliferative phase -Under the influence of Oestrogen the endometrium proliferates and there is an increase in capillary formation in the endometrium •after ovulation the endometrium is also influenced by Progesterone. The endometrium glands become more tortuous and the spiral vessels become more prominent.