The menstrual cycle involves changes in the ovaries and uterus lining controlled by hormones. The pituitary gland releases FSH and LH, stimulating egg development and the production of estrogen and progesterone by the ovaries. Estrogen builds the uterine lining while progesterone maintains it. Around day 14, a surge in LH triggers ovulation. If fertilization does not occur, progesterone and estrogen levels fall, causing the uterine lining to shed through menstruation and initiating a new cycle.

1. The Menstrual Cycle

2. • Describe the menstrual cycle in terms of
changes in the ovaries and in the lining of
the uterus
• Describe the sites of production of
oestrogen and progesterone in the
menstrual cycle and in pregnancy
• Explain the role of hormones in controlling
the menstrual cycle and pregnancy

3. Hormones
• Four hormones involved in controlling
menstruation
Name 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

4. The Cycle
• During the first week of the cycle the
pituitary gland stimulated, and releases
follicle stimulating hormone (FSH)

6. • FSH stimulates a potential egg cell in the
ovary
• The cells around the ovum also develop.
This is called a follicle.
• Follicle cells secrete oestrogen.
• Oestrogen stimulates rebuilding of uterus
wall.
An oocyte (pre-ovum)
surrounded by follicle
cells

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

9. • Initial concentrations of oestrogen are low.
• The low concentration has a negative
feedback effect on the secretion of FSH.

10. Negative feedback lowers
FSH concentration

11. • As follicle grows is produces larger
concentrations of oestrogen.
• At a certain threshold, its effect reverses.
• It now has a positive feedback effect on
secretion of FSH from pituitary.
• Also stimulates pituitary gland to release
luteinising hormone (LH)

13. Positive feedback from
increasing oestrogen
concentration causes
increase in FSH and LH from
pituitary gland.
Follicle gets bigger – releases
more oestrogen

14. • 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.

15. 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

16. • Progesterone completes uterus wall.
Increases blood supply and promotes
glycogen storage.
• Rising concentrations of progesterone and
oestrogen have negative feedback effect
on FSH and LH. This prevents new
follicles forming.

17. 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.

18. • Fertilisation must occur within 2 days of
ovulation.
• Embryo takes 3 days to reach the uterus
and implant.
• If no embryo implants within a week the
corpus luteum starts to break down.
• Progesterone and oestrogen
concentrations fall. Uterus wall begins to
break down.
• FSH no longer inhibited, so begins to rise.
• Cycle begins again

19. 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

20. 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