The menstrual cycle involves coordinated changes in the ovaries and uterus driven by hormones. It typically lasts 28 days and includes a follicular phase where an egg matures and is released, ovulation, and a luteal phase where the corpus luteum develops. Hormones like FSH, LH, estrogen and progesterone regulate this cycle. The endometrium thickens during the follicular phase in response to rising estrogen, and further changes during the luteal phase due to progesterone to prepare for potential implantation. If implantation does not occur, hormone levels drop and the endometrium is shed as menstruation.

1. THE MENSTRUAL CYCLE
Sevag Ouzounian

2. Overview
• Menstrual cycle has evolved to follow lunar cycle – 28
days. This however varies month to month and can be
different in different women
• There is the uterine cycle and the ovarian cycle
• Cycle composed of
• Follicular phase
• Ovulation
• A postovulatory or luteal phase

3. Overview
• Necessities for normal menstrual cycle
• Intact hypothalamo-pituitary-ovarian axis
• Responsive follicles in ovaries
• Functional uterus
• If cycle is prolonged
• Follicular phase will lengthen
• Luteal phase will remain constant at 14 days

4. Hormone Control of Cycle
• Hypothalamo-pituitary-ovarian axis
• Cycle controlled by hypothalamus,
however this can be influenced by
higher centres within the brain
• i.e. due to stress or anxiety
• Hypothalamus releases
gonadotrophin-releasing hormone
in pulsatile manner  anterior
pituitary  release of LH and FSH

5. Hormone Control
• Follicular stimulating hormone (FSH) – glycoprotein
• Stimulates follicular maturation during follicular phase
• Stimulates steroid hormone secretion – oestrogen (by the granulosa
cells of mature ovarian follicle)
• Lutenizing Hormone (LH) – glycoprotein
• Stimulates steroid hormone secretion – oestrogen
• Ovulation – mid-cycle surge of LH
• Progesterone production by corpus luteum
• Negative feedback mechanism controls cycle

6. Ovarian Cycle – Follicular Phase
• Days 1-8 – FSH and LH relatively
high levels
o Stimulate development of 10-20 follicles
o Results in full maturation of a single
dominant follicle – appearing in mid-
follicular phase
o Remainder undergo atresia
o High LH and FSH triggered by drop in
oestrogen and progesterone levels from
last cycle .
o Oestrogen levels start to rise as follicular
development occurs

7. Ovarian Cycle – Follicular Phase (2)
• Days 9-14 –
o Follicle increases in size
o Localized accumulation of fluid among
granulosa cells  fluid-filled central
cavity called antrum
o Transforming primary follicle to Graafian
follicle
o Oocyte occupies excentric position –
surrounded by cumulus oophorus – 2-3
layers of granulosa cells
o Rise in oestrogen by granulosa cells,
associated with follicular maturation
o Inhibin produced by granulosa cells –
restricting number of follicles maturing

8. Ovarian Cycle - Ovulation
• Day 14 – rapid enlargement of follicle
and rupture of the follicle with extrusion
of the oocyte and adherent cumulus
oophorus
• Some women get pain before rupture –
called Mittelschmerz
• Rise in oestrogen  mid-cycle surge of
LH and to a lesser extent FSH 
ovulation
• Immediately before ovulation there is a
drop in oestrogen and an increase in
progesterone.
• Ovulation follows within 18 hours of mid-
cycle surge of LH
• If not enough of a LH surge – then no
ovulation occurs – anovulatory

9. Ovarian Cycle - Luteal Phase
• Days 15-28 – remainder of the
follicle retained in the ovary –
penetrated by capillaries and
fibroblasts from the theca
• Grunlosa cells undergo
luteinization  corpus luteum
formation – the major source of
sex hormones – oestrogen and
progesterone secreted during
postovulary phase
• This leads to marked increase in
progesterone and oestrogen

10. Ovarian Cycle
• If conception and implantation occur:
• Corpus luteum doesn’t regress – maintained by gonadotrophins
secreted by trophoblasts
• If conception doesn’t occur successfully:
• Corpus luteum regresses and menstruation occurs
• Drops in steroid sex hormones  leads to a rise in gonadotrophin
levels (FH and LSH)  initiate next cycle

11. Ovarian and Uterine Cycle

12. Uterine Cycle
• Influenced by the cyclical
production of steroid
hormones
• Causes changes to the uterus
• Involving the endometrium
and cervical mucus

13. Uterine Cycle – Endometrium Overview
• Two layered
• Superficial layer that sheds during the menstrual cycle
• Basal layer that doesn’t take part, but regenerates the superficial
layer
• The basal layer has straight arterioles where as the
superficial layers has spiral ones – important in the
process of shedding

14. Uterine Cycle – Proliferative Phase
• Occurs during follicular phase
of ovarian cycle
• Endometrium exposed to
oestrogen  regeneration
from the last menstrual cycle
• Glands in endometrium are
straight in this phase, parallel
to one another and contain
little secretion

15. Uterine Cycle – Secretory Phase
• After ovulation – progesterone
production causes secretory
changes in endometrial glands
• Appearance of secretory
vacuoles in glandular
epithelium below nuclei
• Secretions in lumen of glands
 which become tortuous and
develop serrated margins

16. Uterine Cycle – Menstrual Phase
• Luteal phase lasts 14 days –
then there is a regression of
corpus luteum  decline in
oestrogen and progesterone
• This leads to a intense
spasmodic contraction of spiral
section of endometrial
arterioles  ischaemic necrosis
 shedding of superficial layer
 bleeding.
• These spasms are associated
with prostoglandin, which are
also associated with increased
uterine contractions during
menstrual flow.

17. Cervical Mucus
• Important to stop ascending infection
• Changes during the menstrual cycle
• Early follicular phase – viscid and impermeable
• Late follicular phase – increasing oestrogen levels  mucus
becomes watery and easily penetrated, allowing spermatozoa to
get through. Change is known as Spinnbarkheit
• Post-ovulation – progesterone from corpus luteum counteracts
oestrogens effects  mucus becomes impermeable and the
cervical os contracts

18. Other Changes
• Body temperature – Rise of 0.5°C after ovulation till onset
of menstruation. Due to progesterone levels. If conception
occurs – this temperature is maintained throughout
pregnancy
• Breast changes – breast swelling during luteal phase due
to increasing progesterone levels
• Psychological changes – change in mood and an
increase in emotional lability. Might be due to falling
progesterone levels.

19. Menses
• Production of 35-80ml of blood
• Over an average of 3-5 days

20. References
• Majority of information from
• Drife, J. & Magowan, B. (2008). The normal menstrual cycle,
Clinical Obstetrics and Gynaecology, Ch11, pp. 121-126
• All images from google.com/images