The Menstrual Cycle

(The uterine cycle)

Three main stages

• Menstrual Stage

• Proliferation Stage

• Secretion Stage

Menstrual Stage (1 day – 5 day)• At the beginning of this stage all the

hormones are at their lowest normal levels but then..

• LH and FSH levels begin to rise

• Endometrium is shed (menses). Why? Hold that thought (if you have one!) until we talk about the Secretory Phase

Downside to menstruation?• Higher iron requirement for women

• Seems wasteful

Proliferation Stage (day 6 – day 14)• LH and FSH Follicle Maturation

• Developing follicle produces estrogen

• Estrogen levels are rising which leads to…

• The endometrium being repaired and thickened.

• Cervical mucus is thinned. Why?• @ end of this stage follicle ruptures (ovulation)

and changes into a corpus luteum. • Basal body temp goes up

Secretory Phase• Progesterone and Estrogen causes the uterine glands and arteries

elaborate and coil. Why? Also thickens cervical mucus. Why?

• P and E also inhibits LH and FSH. What would this do?• Endometrium starts secreting nutrients from glands.• If no implantation takes place the arteries kink up, the cells starve,

their lysosomes rupture and the layer “self-digests”. A gush of blood “flushes” the layer out (signaling the start of the menstrual phase).

• IF a woman gets Premenstrual Syndrome (PMS) this is when it occurs

Discussion Question

• Why doesn’t the “rhythm method” of contraception work very well?

• How does the pill work?

• How might you artificially induce ovulation?

• What can cause the cycle to stop abnormally?

Summary• Hypothalamus

– GnRH – stimulates the release of LH and FSH

• Anterior Pituitary– FSH – Stimulates the development of the follicle

– LH – Stimulates ovulation and development of the follicle

• Ovaries:– Follicle

• Estrogen – Stimulates repair and growth of endometrium.

– Corpus Luteum• Progesterone AND Estrogen – Stimulates growth of and

maintains the endometrium. Inhibits LH and FSH.