The menstrual cycle L5 Flashcards
endocrine control involves 3 things
neuropeptides
glycoproteins
steroids
what is the neuropeptide involved in endocrine control
GnRH
what is GnRH
gonadotropin releasing hormone
where is GnRH released from
the hypothalamus
structure of GnRH
decapeptide (10 aa)
where does GnRh bind
to GnRH receptors expressed in the anterior pituitary gland
3 main glycoproteins controlling endocrine function
LH (luteinizing hormone)
FSH (Follicle stimulating hormone)
CG Chorionic gonadotropin
what are all three glycoproteins
heterodimers
what is the key difference in FSH and LH
share the same alpha chain but different beta chains
what does the difference in beta chains between FSH and LH mean
they can act on different receptors
what also acts on the LH receptor
CG
what type of receptors are the LH and FSH
G protein coupled receptors
whats the common biochemical pre-cursor for steroids
cholesterol
what is cholesterol made from
acetate
four classes of steroids
progestogens
androgens
Oestragens
corticosteroids
how many carbons does progestogens have
21
how many carbons do androgens have
19
how many carbons do oestragens have
18
what is the common synthetic pathway for steroids
acetate—>cholesterol—> common precursor pregneolone
what class is pregneolone
progestogen
what is the precursor of the oestragens
androgens
where does cholesterol synthesis take place
mitochondria
how do neuropeptides and glycoproteins act
on specific receptors
how do steroids act
can go directly through the nucleus
biggest sex organ=
brain
how often is GnRH released after puberty
in hourly pulses
what cells does GnRH act on
gonadotrophs
what are Oocytes contained in
pre-ovulatory follicles
when is Oocyte number fixed
at birth
how many eggs do we have at birth
2 million germ cells
what happens in the absence of the SRY gene
the coelomic epithelia condense around the PGC forming primordial follicles making them stop mitosis
what happens when the primary follicles stop mitosis and begin meiosis
the numbers are fixed
what stage of meiosis do the primary follicles arrest in
half way through meiosis 1 –> DIPLOTENE (prophase 1)
what are they called when they arrest in diplotene
primary oocyte
what happens to many primary follicles before birth
they die
at what point in development are there no more PGC being produced
after 3 months post conception
when does proliferation by mitosis happen
all completed by birth
when does genetic shuffling by meiosis happen
starts in fetal ovary, arrests and restarts at puberty
when does cytodifferentiation happen (making a specialised cell)
completed during ovarian cycle
in a preadolescent what is the hypothalamus like
immature hypothalamus releases slow pulses of GnRH
what do the slow pulses of GnRH from an immature hypothalamus mean
minimal FSH and LH production from pituitary so
no spermatogenesis in male
no ovarian follicle development in females
so…..no testosterone or oestradiol
what is a primordial follicle
primary oocyte
surrounded by a single layer of granulosa cells
what happens to primordial follicles at puberty
they begin to grow
what does the primordial follicle grow to form
primary follicle
the difference in primordial follicles and primary follicle
primary follicle produces thick glycoprotein coat= Zona pellucida
what does the primary follicle form into
preantral follicle
what is the preantral follicle characterised by
proliferation of the granulosa cell
how are a lot of follicles lost
by atresia (degeneration of immature follicles)
What can rescue follicles from atresia
LH and FSH
what does the preantral follicle form
the antral follicle
what is the antral follicle characterised by (3)
the appearance of the antrum
proliferation of granulosa cells
theca cell present
what is the antrum
fluid filled cavity
three types of cell in the antrum=
Oocyte
theca cell
granulosa cells
what are the major hormones regulating female reproductive cycle (3)
FSH
LH
GnRH
when is the Oocyte number fixed
3 months post conception
what is the name of the structure unit in which the oocyte develops
the follicle
at what stage of development are Oocytes at birth
arrested in prophase 1 primary oocytes residing in primordial follicles
what is the pattern of GnRH release in the prepubertal female
irregular
what is the pattern of GnRH release in the postpubertal female
hourly intervals
at what stage of follicle development does ovulation occur
tertiary, preovulatory
how many phases does the ovarian cycle have
2
what are the 2 phases of the ovarian cycle
luteal
follicular
what characterises the luteal phase
progesterone
in the follicular phase what hormone is released first
GnRH
What does GnRH do
cause secretion of FSH and LH from anterior pituitary
What cells have receptors for LH
Theca cells
what cells have receptors for FSH
granulosa cells
what does the binding of LH to theca cells cause
the synthesis of androgens
what do the granulosa do with the androgens from the Theca cells
make oestrogens using aromatase
whats is the oestrogen called that the granulosa cells make
Oestrogen 217 beta
where is Oestrogen 217 beta (E217B) released
into the plasma but with a short half life
what does E217B (oestrogen) do
acts on the anterior pituitary and hypothalamus in a negative feedback loop to regulate LH and FSH production
what other substance do the granulosa cells produce
inhibin B
What does inhibin B do
inhibits the production of FSH from the anterior pituitary
what effect do the androgens have on the granulosa cells
cause proliferation increasing the number of granulosa cells so the follicle grows
in females when is AMH produced and why
post puberty, to regulate the growth of neighbouring follicles
When a follicle expresses FSH and LH receptors that are acted upon what does it become
the dominant follicle that suppressing follicles around it
what does the sharp increase in granulosa cells cause
a sharp rise in oestrogen levels—> plasma oestrogen surge
how does oestrogen act on granulosa cells
in response to high oestrogen levels granulosa cells express LH receptors
when Oestrogen is in very high levels and reaches the threshold what happens
stops negatively inhibiting LH and FSH causing a peak in LH levels
what does the peak in LH levels do
triggers ovulation
what does the peak in LH levels do (2)
triggers ovulation
progesterone production in granulosa cells
overall when E2 is low it does
negative feedback
overal when E2 is high it does
positive feedback
whats it called when the oocyte resumes meiosis and undergoes division
nuclear maturation
how would you describe the division in nuclear maturation
unequal, most cytoplasm retained in secondary oocyte
how much chromosome is lost on the 1st polar body in meiosis
half
what does the presence of a polar body in an oocyte mean
the oocyte is ready to be fertilised
in second meiosis when does the oocyte arrest
metaphase
what happens in oocyte maturation
cytoplasmic maturation (reorganised) -mitochondria and cortical granules relocate to periphery
what happens at the same time as oocyte maturation
associated granulosa cells expand
what is it called when granulosa cells expand
cumulus cell expansion
what happens at the start luteal phase
ruptured follicle forms corpus luteum
what does the corpus luteum secrete
oestrogen and progesterone
how many days does the luteal phase last
14
what happens in the corpus luteum
all the cells of the corpus luteum now express LH receptor, production of oestrogen and rising levels of progesterone —-> negative LH feedback
what happens to the luteal phase after 14 days
it stops unless there is fertilisation and corpus luteal degrades
leutolysis=
break down of the corpus luteum
three stages of the uterine cycle
menstrual phase
proliferation phase
secretory phase
what happens in the menstrual phase
shedding of uterine lining
what happens in the proliferation phase
endometrium and myometrium begin to regrow
increase cervical mucal secretions
what happens in the secretory phase
- blood supply to the endometrial tissues remodelled
- Cervical secretions change again
- supported by progesterone
how many days does it take for the epithelium to be re-epithelialized
4-7 days after the beginning of menstruation
what do progesterones do to the endometrium
cause swellings and secretory development of the endometrium (prepared for implantation)
what is menstruation caused by
the absence of a pregnancy
what is the most potent oestrogen
17-b estradiol
where does 95% of oestrogens come from
granulosa cells
when happens when you run out of eggs
you run out of oestrogen
what are menopausal symptoms principally caused by
lack of oestrogen
example of 3 menopausal symptoms
sleep disturbance
menstrual irregularity
hot flushes
3 long term problems with menopause
osteoporosis
dry vagina
alzheimer’s
In HRT what is oestrogen usually prescribed with and why
progesterone
because oestrogen alone stimulate endometrial hyperplasia and carcinoma
who can take oestrogen only pills
women who have has a hysterectomy
risk of HRT (4)
thrombosis
breast cancer
cardiac disease (older women)
Alzheimers
