implantation and development Flashcards
what happens on day 1 after fertilisation?
first cleavage
what happens on day 2 after fertilisation?
2 cell stage
what happens on days 3-4?
4 cell stage to an 8 cell uncompacted morula
what happens on day 4
8 cell compacted morula
what happens on day 5?
early blastocyst - (trophectroderm, blastocoel, inner cell mass)
what happens on day 6-7?
late stage blastocyst (hatching)
what happens day 8-9?
implantation of the blastocyst
what is transfer of the conceptus through the oviduct facilitated by?
changing endocrine milieu of the early luteal phase with its rising ratio of progesterone to oestrogen, which effects the oviducal and uterine musculature and relaxes the isthmus sphincter.
does the size of the conceptus change as blastomeres are undergoing devisions?
no the total size of the conceptus stays the same.
as a consequence the size of individual blastomeres is reduced progressively.
what happens when the conceptus reaches the maternal endometrium?
attachment and implantation
what is in the structure of a human blastocyst
zona pellucida
blastoceal cavity
inner cell mass
when is pregnancy initiated?
when the conceptus has signalled its presence successfully to the mother.
in the first 14-16 days of human development what are the two cell types types and what do they give rise to?
pluripotent embryonic cells - will give rise to a fetus
they are set apart and enveloped within various extra embryonic cells that will give rise to the supporting structures (mainly the placenta)
when and what is the embryogenic phase of development?
up to day 14
it is the generation of an embryo.
how long does the embryonic phase last for?
6 weeks
what happens during the embryonic phase?
various embryonic cells and tissue types differentiate and the basic body plan is laid down such that eventually tiny foetus formed.
what marks the end of the first trimester?
the transition from embryo to foetus
what are the essential factors for embryo implantation?
the implantation window (receptive endometrium)
healthy embryo at the blastocyst stage
communication between mother and the baby at the time of implantation.
what are the features of a receptive endometrium?
shortening of microvilli
loss of surface negative charge
thinning of the mucin coat
formation of pinopodes
what are the features of a non receptive endometrium
long apical microvilli
high surface negative charge
thick mucin layer
what is decidualization?
post ovulatory process of endometrial remodelling in preparation for pregnancy, which includes secretory transformation of the uterine glands, influx of specialised uterine natural killer cells and vascular remodelling.
what do decidualizing stromal cells acquire the ability to do?
- regulate trophoblast invasion
- resist inflammatory and oxidative insults
- dampen maternal immune responses
in humans when does decidualization of stromal cells occur?
mid luteal phase of the menstrual cycle
independently of pregnancy
what hormone drives decidualization?
progesterone
it drives changes at both transcriptome and proteomic level
when does compaction of the conceptus occur?
around the 8 to 16 cell stage
what does the process of compaction involve?
maximising intercellular contacts and also the transformation of the cell phenotype from radially symmetrical to highly polarised or epithelioid.
what two cell types does the blastocyst contain?
trophoblast cells
inner mast cells
what is the first extra-embronic tissue made up of?
trophoblast cells
the do not contribute to the embryo of foetus
what is the chorion and what is it derived from?
it is an accessory foetal membrane which is concerned with the nutrition and support of the embryo and foetus
it is derived from trophoblast cells
what are the two function of the zona pellucida?
- prevents the blastomeres of the conceptus form falling apart during earl cleavage, before compaction.
- prevents two genetically distinct conceptus from sticking together to make a single chimeric conceptus composed of two sets of cells each of distinct genotype.
where does the blastocyst that has not yet implanted get its oxygen and metabolic subtrees required for growth and survival from?
the uterine secretions that it is bathed in
what are the 3 stages of implantation in humans?
apposition
attachment/adhesion
invasion
what are short range signals
oocyte, sperm, seminal plasma and embryo
what are long range signals?
hormones, nutrition and environmental factors
in humans where does the blastocyst usually implant?
posterior wall of the uterine fundus
what happen during adherence in implantation?
trophoblast cells of the blastocyst adhere to the luminal epithelial cells of the endometrium.
what has to happens before adhesion can occur?
the zona pellucida has to be removed.
where do the enzymes required for the removal of the zona pellucida come from?
trophoblast cells themselves or the uterine secretions
what does attachment induce changes in?
endometrial epithelium and the underlying endometrial stromal tissue
(initiating its development as the maternal component of the placenta)
different species have different types of implantation.
what are they two types of implantation?
invasive and non invasive
which species does invasive implantation occur in?
humans, primates, dogs, cats, mice and rabbits.
the free living blastocyst of the species is relatively short lived
which species does non invasive implantation occur in?
pig, sheep, cow and horse
attachment is initiated later than in invasive conception.
when is hCG synthesised in the the trophoblast of the impacting blastocyst?
as early as 6-7 days after fertilisation.
what is the role of pinipodes?
the may act to absorb uterine fluid to reduce the volume of the uterine cavity and so bring into close apposition the opposing epithelium (occlusion)
when does the receptive phase occur?
day 7 to 10 of menstrual cycle
when is the endometrium said to be prereceptive?
days 1 to 7 of menstrual cycle
which hormone domination is required if the uterus and implanting blastocyst are to engage effectively?
progesterone
what are the molecular messages of attachment?
- firstly - go away messages from the luminal epithelium are switched off in order to remove barriers to attachment and adhesion.
- then come hither messages are sent to promote active engagement of the conceptus.
what is one of the key ‘go away’ messages provided by?
a glycoproteins called Muc1
what is one of the key ‘come hither’ messages in attachment?
leukaemia inhibitory factor (LIF) –> a cytokine produced by the cells of the endometrial glands
what does LIF do?
it permits the cells of the luminal epithelium to respond to local signals from activated blastocysts.
(sensitises the epithelium to the blastocyst)
what are molecular messages of invasion?
MMPs - metalloproteinases - digest stomal components
TIMPs - tissue inhibitors of MMPs - holds MMPs in check.
why is decidualization response by stomal cells at implantation described as resembling a pro inflammatory endometrial reaction?
because prostaglandins which are key players in inflammatory responses are involved in implantation.
what are some molecular messages of invasion other than MMps and TIMPs.
prostaglandins
COX 2
vascular endothelial growth factor (VEGF)
interleukin 11
how long does the fetal phase last for
220 days
what does oestrogen stimulate proliferation and differentiation of?
uterine epithelial cells
what does progesterone stimulate proliferation and differentiation of?
stomal cells
up until which point can progesterone receptor antagonists induce abortion?
7 weeks of gestation.
when does the placenta take over the progesterone production?
approx 12 weeks.
