What are these basic facts about?• The cycle is 28 days long

• The breakdown of uterus lining is triggered by low levels of oestrogen

• Loss of blood and tissue is known as menstruation/ period

• The release of an egg is known as ovulation

Mr. Matthews Wednesday 12 April 2023

The Menstrual Cycle

State the hormones of the menstrual cycle

Understand the basic functions of these hormones

Explain how these hormones affect the female reproductive system

Hormones

• Four hormones involved in controlling menstruationName Made… Function

FSH Pituitary Stimulates one egg cell to develop (become follicle)

Oestrogen Follicle (ovary) Stimulates rebuilding of the uterus wall

LH Pituitary Stimulates follicle to burst and release the ovum

Progesterone Corpus Luteum (ovary) Completes development of uterus wall, promotes glycogen storage

An oocyte (pre-ovum) surrounded by follicle cells

False colour SEM of human uterus wall, approximately 13 days into cycle. Green cells are secretory, and orange cells are ciliated

• Initial concentrations of oestrogen are low.• The low concentration has a negative

feedback effect on the secretion of FSH.

Negative feedback lowers FSH concentration

Positive feedback from increasing oestrogen concentration causes increase in FSH and LH from pituitary gland.

Follicle gets bigger – releases more oestrogen

• Peak of LH causes follicle to burst and release ovum

• This is ovulation (on day 14 of the cycle)• Follicle reforms to become structure called

corpus luteum (‘yellow body’)

• LH stimulates corpus luteum to produce progesterone.

Peak of LH causes ovulation (day 14)

Oestrogen falls because follicle is gone, but corpus luteum still produces some.

Ovulation – ovum released from follicle. Follicle become corpus luteum

Fall in FSH and LH due to negative feedback with oestrogen and progesterone

Progesterone produced by corpus luteum. Inhibits FSH and LH

Corpus luteum – produces progesterone. Uterus wall fully completed.

FSH and LH totally inhibited

Breakdown of corpus luteum causes fall in progesterone and oestrogen

Corpus luteum begins to break down if no embryo has implanted a week after ovulation

FSH begins to rise since it’s not inhibited by oestrogen and progesterone

Low levels of progesterone and oestrogen because there is no follicle or corpus luteum

Uterus wall breaks down due to low levels of oestrogen and progesterone

New egg cell stimulated by rising FSH levels