A summary of the lectures on the hormonal control of the menstrual cycle:
- the phases of the menstrual cycle
- negative feedback and positive feedback of various hormones regulating the phases of the menstrual cycle
The menstrual cycle lasts around 28 The ovaries, which unlike the Ovarian cycle
days and it can be split into three uterus, are glandular and and 1) Follicular phase – pre-ovulation
stages : house cells that produce Days 1-10 .
Menstrual phase – endometrium is endocrine hormones. The The hypothalamus produces GnRH,
shed for the first 5 days ovaries undergo their own cycle stimulating LH and FSH production by
Proliferative phase – building up of known as the ovarian cycle. This the anterior pituitary. These then act
the endometrium is also in 3 phases: on the ovaries to make them produce
Secretory phase – endometrium is Follicular phase – occurs before oestrogen but at LOW levels. This low
at its thickest and there are a lot of ovulation when a follicle is level of oestrogen determines the
secretion from it growing and maturing type of regulation applied to the
The first day is counted as the first Ovulation phase – occur hypothalamus and the anterior
day of menstrual flow and the towards the middle of the cycle pituitary. In this case it is a negative
changes in the uterus are seen in around day 14. A mature follicle feedback. The hormone inhibin is also
the endometrium. releases its ovum. released from the ovaries also has a
Luteal phase – the phase after negative feedback on FSH. This keeps
Ovarian follicles ovulation when the follicle LH and FSH at normal levels and
These are unique structures. The changes its structure and actually causes FS to decrease a bit.
egg forms in a sac-like structure biochemical nature, forming the This is important as it prevents too
called an ovarian follicle. Each corpus luteum. many ovarian follicles maturing at the
follicle contains an oocyte and cells same time.
which produce oestrogen and The hypothalamus and anterior
progesterone. pituitary glands are regulated to
The oogonia are produced in the maintain the right level of
foetal ovaries before birth. These hormones in the blood.
oogonia develop with a sac around
them and they are called Hormonal control of
primordial follicles.
These then develop over time, the menstrual cycle
some before others, as this occurs 2) Follicular phase (late) -just before
3) Luteal phase – after ovulation
through the lifetime of a woman, ovulation
Again the hypothalamus
to become primary follicles. By The hypothalamus produces GnRH
produces GnRH, stimulating LH
puberty, a lot of these are primary which stimulates the production of
and FSH production. This now
follicles (preantral follicles). These LH and FSH. This causes the large
stimulates the Corpus luteum
primary follicles then grow in size Graafian follicle to produce lots of
(formed from the remnants of
so they have more cells for the oestrogen (its highest level in the
the Graafian follicle) to produce
production of hormones. This is cycle) This changes the effect of
very high levels of progesterone.
important as the oestrogen and oestrogen on the hypothalamus and
This affects the endometrium,
progesterone that they release anterior pituitary to have a positive
making sure that it is ready for
keeps this system going. These feedback on the hypothalamus. This
the implantation of a fertilised
cells are celled granulosa cells and causes the LH concentration to
egg.This has a high level of
produce hormones. multiple by nearly 10 – important for
progesterone has a negative
Around 5-10 primary follicles are rupturing the Graafian follicle and the
feedback effect, lowing GnRH,
selected to become larger release of the ovum. The FSH
LH and FSH to basal level. The
secondary follicles. However, not concentration increases much less
positive effects of oestrogen are
all of the follicles finish the cycle as due to the effects of inhibin and it
dominated by the negative
we only want one ova to be has no physiological significance, it is
effects of progesterone.
released. just due to the positive feedback.
If fertilisation occurs the CF is
One follicle matures to become the
maintained by hCG, if not it
Graafian follicle, which is
degenerates.
responsible for the production of
the ovum in this particular cycle as
well as the production of
oestrogen and progesterone. The
non-recruited follicles then die.
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