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• The rapid rise in plasma LH level, known
as the LH surge leads to final maturation
of Graafian follicle.
• Follicle ruptures and a secondary oocyte
is released on about Day 14.
• Shortly after onset of midcycle LH surge,
plasma estradiol levels drop and a further
rise in plasma progesterone occurs.
The uterine lining detaches leading to menstruation It continues usually for 3-5 days. Rapid decrease
in estradiol and progesterone (secreted by corpus
luteum) level induces changes in endometrium. The
blood vessels rupture causing bleeding. The uterine
tissue and blood, tissue fluid from the endometrial
surface pass out through vaginal opening, constituting
menstrual flow.
• Ovarian follicles begin to enlarge through
proliferation of their granulosa cells.
• The FSH stimulates ovarian follicle to secrete
estrogen, that stimulates the proliferation of
the endometrium of the uterine wall.
• New blood capillaries develop and the epithelial
lining of oviduct develops more cilia. The activity
of secretory cells is enhanced. Muscles of the
genital tract become more active. Cervix develops
mucous strings which form channels for guiding
movements of sperms.
• Following ovulation, LH stimulates the
remnants of ovulated follicle to develop
into corpus luteum, which secretes
progesterone and some estradiol.
• Both LH and progesterone help in further
growth and thickening of endometrium.
The major change is that the endometrial
glands become secretory.
• The uterine wall becomes ready for
nourishing and anchoring blastocyst if
fertilisation takes place.
• Progesterone inhibits uterine movements
as well as proliferation of new ovarian
follicles. The phase lasts for about 10 days.
• If the oocyte is not fertilised, corpus luteum
activity declines and it degenerates into
corpus albicans.
• With decrease in ovarian hormones,
release of GnRH, FSH, and LH occurs due
to loss of negative feedback suppression
by ovarian hormones. This resumes
follicular growth.
Beginning
of cycle
Fig.: Schematic representation of menstrual cycle
Ovulation
Growing follicle
Luteinising hormone (LH)
Estrogen Progesterone
Menses Menses
Follicular phase Luteal phase
14 days 28 days
Ovulation
0 days
Follicle-stimulating
hormone (FSH)
37°C
36°C
Ovarian cycle
Body temp.
Anterior pituitary
hormones
Ovarian hormones
Uterine cycle
Ovulation Corpus luteum Corpus albicans
Fig.: Summary of events during a menstrual cycle
Endometrium
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