Female reproductive system Flashcards
Outline the progression from primordial germ cell to mature oocyte
(oogenesis)
- primordial germ cell
- oogonia/ primordial ova
- primary oocyte/ primordial follicle
- secondary oocyte
- mature oocyte
Describe the first step of oogenesis
1.
2.
3. primary oocyte/ primordial follicle
4. secondary oocyte
5. mature oocyte
- Primordial germ cells divide repeatedly as migrate from dorsal endoderm of yolk sac, along hindgut to outer surface of ovary
- migrate into ovarian cortex, become oogonia/primordial ova
Another term for oogonia
primordial ova
Describe the second step of oogenesis
- primordial germ cell
- primary oocyte
- secondary oocyte
- mature oocyte
Each primordial ovum collects a layer of spindle cells from ovarian stroma, forming a single layer of flattened follicular cells, called granulosa cells
Describe the third step of oogenesis
- primordial germ cell
- oogonia/ primordial ova
- secondary oocyte
- mature oocyte
Oogonia/primordial ova enlarge to form primary oocytes
The primary oocyte + granulosa cells= primordial follicle
How many primary oocytes are there at peak and at birth, why? and why no more after birth?
week 20 peak= 7 million primary oocytes
cell death occurs from this point
birth= 2 million
no primary oocytes form after birth as germ cell mitosis ceases
what happens with the primary oocyte between birth and puberty?
(oogenesis)
at birth, primary oocytes begin meiosis 1, arrested late prophase 1
primary oocytes remain dormant in ovary until puberty
why does meiosis 1 in primary oocyte resume at puberty?
meiosis 1 resumes in primary oocyte due to production of FSH and LH at puberty, just before first ovulation
how does primary oocyte become secondary oocyte?
with meiosis 1, division of cytoplasm is unequal, a large secondary oocyte and a small first polar body are formed
polar body is non functional and disintegrates
what happens to the secondary oocyte at first?
secondary oocyte begins meiosis 2 but arrests in metaphase 2
when does meiosis 2 of secondary oocyte complete? what happens
if fertilisation occurs after ovulation, meiosis 2 completes, releases mature oocyte and a small second polar body
what is the difference between the first and second polar bodies produced in meiosis 1 and 2 of oocytes
first polar body contains full set of chromosomes
in the second polar body, chromosome number is halved between mature ovum and second polar body
do all oocytes become mature?
only a small percentage become mature.
those that don’t become acretic (degenerate)
400-500 will become mature during reproductive years
oogenesis occurs alongside - ?
oocytes grow and mature alongside folliculogenesis
what do the granulosa cells do in the primordial follicle?
thought provide nourishment and secrete maturation inhibiting factor
how are primary oocytes recruited for folliculogenesis?
there is continuous recruitment of primary oocytes up to ovulation, takes 7-9 months
Outline the progression from primordial follicle to mature follicle
- primordial follicle
- primary follicle
- secondary follicle
- antral follicle
- mature follicle
how is the primordial follicle formed
primordial ova collects layer of spindle cells, forming flattened follicular cells- granulosa cells
primordial ova enlarges to become primary oocyte
primary oocyte + granulosa cells= primordial follicle
What is the second step of folliculogenesis?
- primordial follicle
2.
- secondary follicle
- antral follicle
- mature follicle
primordial follicle becomes primary follicle through enlargement of the ovum and growth of additional layers of granulosa cells
zona pellucida appears here too
how do primary follicles become secondary follicles? ie what is step 3
- primordial follicle
- primary follicle
3.
- antral follicle
- mature follicle
FSH and LH increase first few days of monthly cycle, ► accelerated growth 6-12 primary follicles each month
rapid proliferation of granulosa cells, so many more layers-
spindle cells collect in layers around the granulosa cells creating the theca
what are the 2 parts of the theca on the secondary follicle
theca interna: epitheliod characteristics, secretes oestrogen and progesterone
theca externa: highly vascular connective tissue capsule
what is step 4 of folliculogenesis
what happens after the secondary follicle has developed the theca?
- primordial follicle
- primary follicle
- secondary follicle
4.
- mature follicle
granulosa cells secrete follicular fluid with high oestrogen concentration
causes an antrum to appear. = antral follicle
growth is accelerated, vesicular follicles form
what happens once we have an antral follicle?
- primordial follicle
- primary follicle
- secondary follicle
- antral follicle
5.
one follicle begins to outgrow the others. once others have degenerated, this is the mature follicle
what happens to the remainder of the follicles when one becomes the mature follicle, why
remainder involute in atresia (degenerate)
likely due to positive feedback loop
usually prevents more than 1 child per pregnancy
what type of follicle cell is this and why?
(folliculogenesis)
primordial follicle
-only primary oocyte and single layer granulosa cells
what type of follicle cell is this and why?
(folliculogenesis)
primary follicle
-more layers of granulosa cells but no theca or antrum
what type of follicle cell is this and why?
(folliculogenesis)
antral follicle
- has an antrum but not very big yet
what type of follicle cell is this and why?
(folliculogenesis)
mature follicle
has big antrum and theca
what type of follicle cell is this and why?
(folliculogenesis)
primordial follicle
only a thin layer of granulosa cells and oocyte
what type of follicle cell is this and why?
(folliculogenesis)
primary follicle
-more granulosa cells, zona pellucida
what type of follicle cell is this and why?
(folliculogenesis)
secondary follicle
-theca has developed, no antrum yet
what type of follicle cell is this and why?
(folliculogenesis)
mature oocyte
- large antrum
talk me through this image
sweet
basic definition of menstrual cycle?
mestrual cycle= the regular changes in activity of ovaries and endometrium that make reproduction possible, occurs monthly
what does the menstrual cycle consist of
2 interconnected and synchronised processes, ovarian cycle and uterine/endometrial cycle
purpose of ovarian cycle
development of follicles and ovulation
purpose of uterine/endometrial cycle
thickening and shedding of endometrium
what are the pre-ovulatory phases
ovarian cycle: follicular phase
uterine cycle: menstrual and proliferative phases
what are the post ovulatory phases of the menstrual cycle
ovarian cycle: luteal phase
uterine: secetory phase
which cycle and phase is the follicular phase
ovarian cycle, pre ovulatory
which cycle and phase is the luteal phase
ovarian cycle, post ovulatory
which cycle and phase is the menstural phase
uterine/endometrial, pre ovulatory
occurs first
which cycle and phase is the proliferative phase
uterine/endometrial, pre ovulatory
occurs after menstrual phase
which cycle and phase is the secretory phase
uterine/endometrial, post ovulatory
fill in the blanks
when does menarche occur
11-15
explain the time periods of the menstrual cycle
onset at menarche, age 11-15
occurs monthly, only pauses for pregnancy
stops at menopause age 50
avg length menstrual cycle
28 days
what is day 1 of the menstrual cycle
day 1 is the first day on menstruation
on what day does ovulation occur
14 days before first day of menstruation
in avg 28 day cycle this is day 14
GnRH
GnRH= Gonadotrophin releasing hormone
secreted in pulses by hypothalamus
pulses vary in frequency and magnitude
cause anterior pituitary to release FSH and LH in pulsatile fashion according to freq/mag
what hormones do LH and FSH stimulate in menstrual cycle?
FSH and LH stimulate oestrogen and inhibin
what do oestrogen and inhibin do in the menstrual cycle?
inhibit GnRH production and therefore LH and FSH
what does FSH do in menstrual cycle?
stimulate follicular development
what does LH do in menstrual cycle?
LH causes Graafian follicle to become corpus luteum which then produces progesterone
what does progesterone do in the menstrual cycle
stimulate endometirum more receptive to implantation of fertilised ovum
negative feedback cycle LH, FSH, oestrogen, inhibin
increased oestrogen, inhibin, progesterone have negative feedback effect on hypothalamus, causes decreased GnRH, so less LH and FSH, leads to less oestrogen and inhibin
identify the theca cells and granulosa cells on this secondary follicle.
which receptors do they have
theca cells have LH receptors
granulosa cells have FSH receptors
what is the first thing that happens in follicular phase?
theca cells develop LH receptors
granulosa cells develop FSH receptors
GnRH pulses increase, causing FSH levels to rise, stimulates 6-12 follicles to mature at accelerated rate
what do the theca and granulosa cells do in response to FSH and LH
follicular phase
LH causes theca cells to produce androstendione
FSH causes granulosa cells to produce aromatase
aromatase converts androstendione to oestrogen
granulosa cells then also develop LH receptors
what happens once the theca and granulosa cells are producing oestrogen
follicular phase
as follicles grow, more and more oestrogen is produced
this has negative feedback effect on hypothalamus, so less GnRH, less FSH and less FH
what does the reduction in FSH and LH mean
follicular phase
with less FSH some developing folicles degenerate
follicle with the most FSH receptors continues to grow, becomes the most dominant follicle, the Graafian follicle
what happens once we have a graafian follicle
follicular phase
graafian follicle secretes increasing amounts of oestrogen, surpasses a threshold level
this causes an LH surge and a lesser FSH surge
causes rapid swelling of graafian follicle
what happens after the LH surge
follicular phase
ovulation!
high LH causes membrane of graafian follicle to thin, alongside increased follicular pressure
causes a stigma to form which expands, ruptures and expells the secondary oocyte
what happens to the oocyte once LH surges
follicular phase
primary oocyte completes meiosis 1, secondary oocyte is expelled and guided to fallopian tube by fimbriae
ie, ovulation
what does the uterine cycle do
prepare the endometrium for implantation and maintenance of pregnancy
what is the endometrium and its parts
endometrium is the inner lining of the uterus, has 2 layers:
functional layer- grows thicker in response to oestrogen, sheds in menstruation
basal layer- forms foundation from which functional layer develops
what does the degeneration of the corpus luteum (from luteal phase of previous cycle) result in
menstrual phase
degeneration of corpus luteum results in decreased progesterone production
what does decreased progesterone trigger
menstrual phase
spiral arteries in functional endometirum contract
so blood supply lost, functional endometrium becomes ischaemis and necrotic
is shed, exits through vagina as menstruation
what occurs in the proliferative phase
uterine cycle
high oestrogen levels (bc of follicular phase) stimulate thickening of endometrium, growth of endometrial glands and increased vascularity- ie reemergence of spiral arteries
rising oestrogen makes cervical mucus consistency more hospitable to spem
what happens to the follicle once the oocyte has been expelled
luteal phase
remnants of follicle become corpus luteum-
the theca and granulosa cells become luteinised by LH surge
what do the luteinised theca and granulosa cells do in corpus luteum
luteal phase
luteinised theca cells continue secreting androstendione, luteinised granulosa cells contune aromatase, converting the androstendione to oestrogen
however, luteineisedgranulosa cells in low LH conditions increase activity of cholesterol enzyme
what happens when luteinised granulosa cells increase activity of cholesterol enzyme
luteal phase
cholesterol enzyme converts cholesterol to pregnenolone, a precursor for progesterone, so more progesterone is produced
how does progesterone become dominant over oestrogen in luteal phase
progesterone has negative feedback effect on HPG axis, so FSH and LH decreases, so less oestrogen
luteinised granulosa cells secrete inhibin, further inhibiting FSH and so oestrogen production
so progesterone is dominant
what marker is there that progesterone is dominant
progesterone increases basal temp
what happens to the corpus luteum as FSH and LH levels fall, what does this cause
luteal phase
corpus luteum degenerates into non functional corpus albicans
causes loss of progesterone production, triggers menstruation
what happens differently post ovulation in ovarian cycle in ovum is fertilised
fertilised ovum produces hCG which has similar function to LH
this prevents degeneration of corpus luteum so there is continued production of progesterone, preventing menstruation
placenta eventually takes over role of corpus luteum
what happens in secretory phase of uterine cycle
high levels of progesterone from corpus luteum drives more secretions from endometrial glands that make uterus more welcoming for implantation
further thickening of endometrium and myometrium
reduction of motility of myometrium
thick acidic cervical mucus production to prevent polyspermy
summarise the follicular phase of ovarian cycle
- GnRH increases so FSH and LH increase
- LH= theca cells produce androstendione and FSH= granulosa cells produce aromatase which converts androstendione to oestrogen
- oestrogen negative feedback on GnRH, LH, FSH, only follicle with most FSH receptors becomes dominant, rest degenerate
- graafian follicle secretes lots of oestrogen, triggers LH surge
- LH surge raises pressure of and thins membrane of follicle, oocyte expelled
summarise the luteal phase of the ovarian cycle
- remnants of follicle become corpus luteum
- luteinised theca and granulosa cells continue producing oestrogen with androstendione and aromatase
- granulosa cells in low LH increase activity of cholesterol enzyme
- this converts cholesterol to pregnenelone, a precursor for progesterone
- progesterone levels rise, has negative feedback on HPG axis so less gnrh, fsh, lh, oestrogen, progesterone is dominant
- fsh and lh levels fall, corpus luteum degenerates into corpus albicans, loss of progesterone, triggers mensturation
summarise the menstrual phase of uterine cycle
- degeneration of corpus luetum causes decreased progesterone
- causes spiral arteries in function endometrium to contract
- becomes ischaemic and necrotic
- sloughs off, exits through vagina
summarise the proliferative phase of uterine cycle
- high oestrogen levels from graafian follicle stimulate thickening of endometrium, growth of endometrial galnds, increased vascularity as spiral artieries reemerge
- oestrogen changes cervical mucus consistency so more hospitable to sperm
summarise secretory phase of uterine cycle
- progesterone from corpus luteum means gands secrete substances that make uterus more welcoming for implantation but thick acidic mucus production to prevent polyspermy
further thickening of endometrium/myomtrium
GnRH
gonadotrophin releasing hormone
released steadily until puberty, then in pulses
releases FSH and LH from anterior pituitary
frequency and mag of pulses determine how much
FSH
follicle stimulating hormone
stimulates follicular dev
causes granulosa cells to produce aromatase (converts ondrostendione to oestrogen)
therefore increased fsh goes to increased oestrogen
LH
luteinising hormone
LH causes theca cells to produce androstendione, converted by aromatase to oestrogen
LH surge thins follicle mebrane, leads to ovulation
luteinised granulosa cells in low LH cause more progesterone
oestrogen re follicles
androstendione from theca cells converted by aromatase from granulosa cells into oestrogen
has negative feedback on hypothalamus, so less GnRH, less FSH and LH so less oestrogen
rising oestrogen causes LH surge and so ovulation
oestrogen re endometrium
stimulates thickening and vascularity of endometrium
makes cervical mucus more hospitable to sperm, optimises fertilisation
progesterone re menstrual cycle
more prog= less oestrogen as negative feedback on HPG axis (gnrh to fsh and lh to oestrogen)
made by luteinised granulosa cells in low LH- chol enzyme turns chol to pregnenelone to prog
increases basal temp
progesterone re endometrium
makes endometrium more receptive to implantation
thickens endometrium and myometrium
degeneration of corpus luteum= loss prog= vasoconstriction spiral arteries= sloughs off= period
