Fertilisation Flashcards
what is cervix in relation to uterus
narrowest region
what is from cervix leading to outside
vagina
what is structurally in the outer edge of ovary called
cortex
what is structurally on inside of ovary & their overall function
blood vessels, nerves, CT - to take hormones away from ovary (oestrogen, progesterone) to enter systemic circulation
functions of ovary
- development of follicles
- production of oestrogen and progesterone
what does ovary cortex contain
developing follicles
what is a follicle composed of
oocyte w/ supporting follicular cells surrounding
list types of follicles from most immature to most mature
- primordial follicle
- primary follicle
- secondary follicle
- tertiary follicle
what are general structural changes that occur as follicle develops
- increasing oocyte size
- increase number of follicular cells around oocyte
what is a change in secondary and tertiary follicles seen in particular
- in secondary and tertiary follicles, there some space between follicular cells = antrum
what is the antrum
- filled with fluid
- supports developing oocyte
describe ovulation in regard to folllciles
- when tertiary follicle ruptures
- oocyte w/ some supporting follicular cells is released from ovary
- makes way into fallopian tubes / oviduct (where can meet sperm & fertilisation occur)
- remnants of tertiary follicle that stays behind in ovary - cells collapse in on one another => corpus luteum
function of corpus luteum
makes hormones
lifespan of corpus luteum if no pregnancy
~14 days if fertilisation and implantation not occur
- after 14 days degenerates into bit of scar tissue => corpus albicans
lifespan of corpus luteum if pregnancy
- if fertilisation and implantation does occur, corpus luteum kept alive >14 days
what cells in the ovary are responsible for oestrogen and progesterone production and when briefly
follicular cells but at different points in follicle development
follicular cells within ovary make oestrogen during which follicles
follicular cells in:
primordial follicle
primary follicle
secondary follicle
tertiary follicle
follicular cells that make oestrogen ONLY make oestrogen - true or false
true
ONLY oestrogen is made before ovulation [by follicular cells in ovary] - true or false
true
what follicular cells are progesterone not made by
follicular cells in:
primordial follicles
primary follicles
secondary follicles
tertiary follicles
what follicular cells make progesterone
- remaining follicular cells in corpus luteum after ovulation make oestrogen and now progesterone
oestrogen and progesterone are made after ovulation [by follicular cells in ovary] - true or false
true
progesterone is only made after ovulation [by follicular cells in ovary] - true or false
true
what hormone is made before ovulation?
what hormones are made after ovulation?
- before: oestrogen
- after: oestrogen, progesterone
[regulation of the female reproductive cycle] what does hypothalamus make? which acts on?
gonadotrophin releasing hormone (GnRH)
acts on anterior pituitary
[regulation of the female reproductive cycle] what does anterior pituitary dominantly make during follicular phase? triggered by what? acts on what?
- due to GnRH release from hypothalamus
- anterior pituitary releases follicle stimulating hormone (FSH)
- FSH stimulates development of follicles in ovary
result of FSH stimulation in ovary on oestrogen
- follicles get bigger
- produce more and more oestrogen
what does increased oestrogen produced by the developing follicles (due to FSH stimulation) do?
- oestrogen goes to uterus
- stimulate proliferation of stratum functionalis layer of uterus
[regulation of the female reproductive cycle] what does anterior pituitary dominantly make during [ovulation and] luteal phase? triggered by what? acts on what?
- due to GnRH release from hypothalamus
- anterior pituitary releases luteinising hormone (LH) just before day 14 of cycle
- LH surge causes ovulation - tertiary / Grafiaan follicle ruptures & oocyte released
what does progesterone (made by follicular cells in corpus luteum) do
- switches on the glands in stratum functionalis layer of uterus
- tells them to start making glucose-rich mucous
what is the function of the glucose-rich mucous produced by uterine glands (turned on due to progesterone)
- glucose as energy source for an egg & potentially fertilised egg and early embryo
- until placenta develops
does corpus albicans make any hormones (assuming no pregnancy) & what does this indicate
- no
=> no more oestrogen and progesterone made at this part of reproductive cycle
if there is formation of corpus albicans, and no oestrogen or progesterone is made any longer what does this mean for menstruation and why
- menstruation occurs
- since no oestrogen or progesterone to keep wall of endometrium (uterine lining) alive
what can ovarian cycle be split into - brief and non brief
brief: follicular phase (incl menstrual phase and ovulation) & luteal phase
non-brief:
- menstrual phase (bleeding occurs - shedding of endometrium lining from past cycle)
- follicular phase
- ovulation (marks release of oocyte; transition from follicular phase to luteal phase)
- luteal phase
what needs to occur that otherwise doesn’t, if fertilisation occurs
keep uterus alive
sperm needs to be _________________ for fertilisation to occur
deposited into female reproductive tract
what occurs for sperm to be deposited into female reproductive tract
ejaculation
how long following semen deposition will you find sperm entering cervix (bottom part of uterus)
~1 minute
how does sperm enter cervix following deposition
- uterus contracts
- moving part of cervix down into vagina
- contraction helps pick some sperm up from vagina to bring into [bottom part of] uterus
how is sperm stored in uterus
stored in cervical crypts for some time
how can sperm stay stored in cervix (cervical crypts)
- nourished by cervical mucous
- to keep sperm alive
describe the cervical mucous and its function before ovulation
- white, very thick - acts as barrier for sperm penetrating and entering uterus
- since before ovulation, oocytes still developing
(=> no point having sperm penetrate and enter uterus as no oocytes are ready for fertilisation)
describe the cervical mucous and its function at time of ovulation
- clear, slippery, thin - sperm can pass thru easily
- since ovulation occurring, now oocyte in ovarian duct
- want sperm to enter uterus so can try meet with and fertilise with egg
how long can sperm survive for / viable in female reproductive tract
~48 hrs
lifespan of oocyte viability
~14hrs
why is there so many sperm within an ejaculate / semen when only takes one sperm to fertilise an egg
majority of sperm lost
list ways sperm is lost on way to oocyte
- destroyed by vaginal acid (vaginal env acidic)
- fail to penetrate cervical mucous
- destroyed by defence cells (sperm = foreign cells in female body)
- enter ‘wrong’ oviduct
why will sperm enter ‘wrong’ oviduct
- ovulation occurs from one oviduct (where oocyte is)
how does sperm move thru female reproductive tract
- sperm are motile by tail lashing
- research that sperm movement aided by female physiology - uterine contractions; chemical attractants
describe how uterine contractions can aid in sperm movement
contractions of muscles in uterus can help push sperm up towards oviduct
describe how chemical attractants can aid in sperm movement
- oocyte and surrounding follicular cells may release some chemical attractants which help draw sperm towards oocyte
what are the regions the oviduct are divided into (from closest to uterus to out)
- isthmus - site of capacitation
- ampulla - site of fertilisation; longest part of oviduct
- infundibulum (contains fimbriae - pick up oocyte at ovulation)
what is capacitation
sperm maturation
what happens when sperm reach isthmus
- sperm stored ~10hrs until ovulation occurs
- undergo additional maturation step - ‘capacitation’- before can enter ampulla & fertilise egg
if capacitation doesn’t occur can sperm fertilise an egg
no
ie/ essential for fertilisation
what 2 events occur in capacitation
- sperm become hyperactive; tails beat more vigorously
- sperm prepare for acrosome reaction
describe why sperm becoming hyperactive is important in capacitation
- have more force when swimming now
=> more power to break thru protective coats around oocyte (can penetrate thru follicular cells surrounding oocyte in oviduct to reach oocyte)
describe acrosome reaction of sperm
- release of enzymes from acrosome by rupturing
- required for sperm to reach oocyte
what is acrosome
- organelle in sperm head, above its nucleus
- bag of digestive enzymes
what is zona pellucida
- oocyte protein coat
- gelatinous protein coat
- protective layer
- surrounds and protects oocyte
- surrounded by (protective) layers of follicular cells
what must sperm overcome to reach oocyte (consider capacitation)
- get thru follicular cells, get thru zona pellucida
- before can bind to and fertilise oocyte
why is it important to have protective coats around egg regarding sperm
- don’t want abnormal sperm reaching oocyte
- only good healthy sperm will get through all protective layers to reach oocyte
what are the layers the sperm has to penetrate in acrosome reaction
- between follicular cells
- zona pellucida
what are the events in acrosome reaction (5)
1 - sperm approaches follicular cells (acrosome becomes leaky, some digestive enzymes from acrosome escape -> break connecting junctions between follicular cells -> follicular cells separate as no longer tightly connected -> sperm w/ hyperactive tissue can burrow through betwen follicular cells)
2 - acrosome ruptures -> all remaining digestive enzymes escape from acrosome & bind to zona pellucida -> digestive enzymes digest a hole through zona pellucida -> sperm can push its way thru zona pellucida via tunnel to reach oocyte
3 - fertilisation occurs - sperm head w plasma membrane touching / binds oocyte plasma membrane
4 - sperm enters oocyte (nuclear material - egg pronuclei & sperm pronuclei -> form a single nucleus)
5 - polyspermy blocked (don’t want more than one sperm fertilising an egg) - via 1. depolarisation (sodium influx) at fertilisation) & 2. cortical granule reaction (calcium influx) hardens zona pellucida at fertilisation
describe depolarisation in polyspermy blocking in detail
- when plasma membrane of sperm binds w plasma membrane of egg
- sodium rushes into egg (sodium influx)
- causes egg to depolarise (electrical signal change)
- [electronically] repels any sperm that might be part way thru zona pellucida
describe cortical granule reaction in polyspermy blocking in detail
- very edge of oocyte underneath plasma membrane (ie/ within oocyte) contains little spheres - cortical granules
- when fertilisation occurs, calcium influxes into egg causing cortical granular reaction
- when fertilisation occurs, cortical granules move to surface & release granular material into space between zona pellucida and oocyte
- cortical granular material binds to zona pellucida -> changes way proteins interact within zona pellucida (composition) -> hardens zona pellucida
- sperm that part way through zona pellucida find it impossible to burrow through ie/ progress to meet egg stops
- zona pellucida was soft and jellylike -> now very hard
when is second polar body ejected
fertilisation - where meiosis II continues
cell progression at fertilisation
sperm and egg pronuclei -> become 1 cell (zygote)
- 2 haploid gametes form to make 1 diploid zygote
1 cell -> 2 cells
2 cells -> 4 cells
(undergoing mitotic divisions to lead to formation of an embyro)
what is cleavage
- cell division of fertilised egg into two cells -> four cells -> eight cells -> etc
what level of oocyte is ovulated
secondary oocyte
(in tertiary follicle)
what occurs at day 0 of fertilisation
- ovulated secondary oocyte in oviduct plasma membrane is met by plasma membrane of sperm that has travelled into oviduct = fertilisation
- sperm travels into oocyte
- formation of zygote (fertilised egg) (2 haploid pronuclei join to form diploid single cell)
what occurs day 1 (24hrs) fertilisation. what is this known as
- zygote divides into 2 cells
- part of cleavage
what occurs day 2 (48hrs) fertilisation. what is this known as
- 2 cells divide again into 4 cells
- part of cleavage
what happens 3 days (72hrs) fertilisation. what is this known as
- 4 cells divide again into 8 cells
- part of cleavage
timeframe that cleavage occurs
cell division in first three days after fertilisation
what happens at day 4 of fertilisation
- cells still divide
- ball of cells - ‘morula’
what is still present from day 0 to day 4 after fertilisation
zona pellucida still present around dividing cells
as the days pass after fertilisation, and the morula forms where is this occuring
- moving down oviduct toward uterus
- dividing cells in morula are still within oviduct
- morula enters into uterus
where don’t we want implantation to occur & what would be the result
- don’t want implantation to occur in oviduct
- would cause ectopic pregnancy - dangerous
what is the significance of the zona pellucida surrounding the dividing cells after fertilisation in regard to implantation
- zona pellucida stops these embryonic cells from binding to wall of oviduct
- so that implantation does not occur here
what occurs day 5 after fertilisation
- blastocyst
- that is within uterus
- zona pellucida has dissolved
why would the zona pellucida dissolving by day 5 be appropriate
- by day 5 the embryonic cells are located (as a blastocyst) in the uterus
- want implantation to occur in uterus
- zona pellucida would block this
what is the difference between blastocyst and morula
- morula was solid ball of cells
- blastocyst structure has fluid-filled space in centre
what happens day 6 after fertilisation
- blastocyst implant into wall of uterus => implantation occurs
explain which part of blastocyst implants into wall of uterus in regards to structure
- one side of blastocyst will contain cluster of cells - this implants into uterine wall / wall of endometrium
- other side blastocyst only has one layer of cells
- fluid-filled space in middle / toward emptier cell side
endometrium is which layer of uterine wall
innermost
what is above the endometrium
lumen
centre of uterus
what are the outer cells of the blastocyst called and what do they become
- trophoblast cells
- will become foetal part of placenta
what is the placenta
- structure that supports and protects embryo and then focetus
what is placenta made from
- partly from blastocyst trophoblast cells
- partly made from mother
what are the cluster of cells in the blastocyst (side that implants into endometrium) called and what do they become
- embryoblast cells
- become embryo itself
(note: cluster of same cells)
what happens in early days after implantation
- embryoblast cells begin to differentiate (they not all same)
- trophoblast cells at base where blastocyst implants into wall of endometrium begin to differentiate into 2 populations - cytotrophoblast cells that continue to become part of foetal placenta (smaller than trophoblast cells); new layer of cells emerge (from trophoblast cells) called syncitotrophoblast cells that secrete digestive enzymes that digest a space into endometrium of uterus for blastocyst to actually implant in (hence blastocyst burrowed into wall of endometrium) & secrete hCG (human chorionic gonadotropin) hormone that only found in blastocysts => only found in pregnancy - keeps corpus luteum alive within ovary
what hormone keeps corpus luteum alive beyond 14 days
hCG that made by syncitotrophic cells of blastocyst
how does keeping corpus luteum alive prevent uterine wall from shedding during menstruation
- corpus luteum produces progesterone
- which prepares uterine wall for implantation
- if corpus luteum turns into corpus albicans and progesterone level drop (+ oestrogen drop), which would lead to endometrial lining shedding
what are the 2 requirements that result in hCG being produced
- fertilisation and implantation occurring
what hormone is looked for in a pregnancy test to confirm pregnancy - both urine and blood
hCG
what does positive hCG reading indicate and why
- pregnancy
- that a fertilised egg has implanted into wall of uterus
blastocyst ends up completely within wall of endometrium after burrowing into it during implantation process. true or false. what allows this to happen
true
- digestive enzymes of syncitotrophic cells create space for it
