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
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.
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
