implantation and development

Question 1

what happens on day 1 after fertilisation?

Answer 1

first cleavage

Question 2

what happens on day 2 after fertilisation?

Answer 2

2 cell stage

Question 3

what happens on days 3-4?

Answer 3

4 cell stage to an 8 cell uncompacted morula

Question 4

what happens on day 4

Answer 4

8 cell compacted morula

Question 5

what happens on day 5?

Answer 5

early blastocyst - (trophectroderm, blastocoel, inner cell mass)

Question 6

what happens on day 6-7?

Answer 6

late stage blastocyst (hatching)

Question 7

what happens day 8-9?

Answer 7

implantation of the blastocyst

Question 8

what is transfer of the conceptus through the oviduct facilitated by?

Answer 8

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.

Question 9

does the size of the conceptus change as blastomeres are undergoing devisions?

Answer 9

no the total size of the conceptus stays the same.

as a consequence the size of individual blastomeres is reduced progressively.

Question 10

what happens when the conceptus reaches the maternal endometrium?

Answer 10

attachment and implantation

Question 11

what is in the structure of a human blastocyst

Answer 11

zona pellucida
blastoceal cavity
inner cell mass

Question 12

when is pregnancy initiated?

Answer 12

when the conceptus has signalled its presence successfully to the mother.

Question 13

in the first 14-16 days of human development what are the two cell types types and what do they give rise to?

Answer 13

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)

Question 14

when and what is the embryogenic phase of development?

Answer 14

up to day 14

it is the generation of an embryo.

Question 15

how long does the embryonic phase last for?

Answer 15

6 weeks

Question 16

what happens during the embryonic phase?

Answer 16

various embryonic cells and tissue types differentiate and the basic body plan is laid down such that eventually tiny foetus formed.

Question 17

what marks the end of the first trimester?

Answer 17

the transition from embryo to foetus

Question 18

what are the essential factors for embryo implantation?

Answer 18

the implantation window (receptive endometrium)
healthy embryo at the blastocyst stage
communication between mother and the baby at the time of implantation.

Question 19

what are the features of a receptive endometrium?

Answer 19

shortening of microvilli
loss of surface negative charge
thinning of the mucin coat
formation of pinopodes

Question 20

what are the features of a non receptive endometrium

Answer 20

long apical microvilli
high surface negative charge
thick mucin layer

Question 21

what is decidualization?

Answer 21

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.

Question 22

what do decidualizing stromal cells acquire the ability to do?

Answer 22

• regulate trophoblast invasion
• resist inflammatory and oxidative insults
• dampen maternal immune responses

Question 23

in humans when does decidualization of stromal cells occur?

Answer 23

mid luteal phase of the menstrual cycle

independently of pregnancy

Question 24

what hormone drives decidualization?

Answer 24

progesterone

it drives changes at both transcriptome and proteomic level

Question 25

when does compaction of the conceptus occur?

Answer 25

around the 8 to 16 cell stage

Question 26

what does the process of compaction involve?

Answer 26

maximising intercellular contacts and also the transformation of the cell phenotype from radially symmetrical to highly polarised or epithelioid.

Question 27

what two cell types does the blastocyst contain?

Answer 27

trophoblast cells | inner mast cells

Question 28

what is the first extra-embronic tissue made up of?

Answer 28

trophoblast cells | the do not contribute to the embryo of foetus

Question 29

what is the chorion and what is it derived from?

Answer 29

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

Question 30

what are the two function of the zona pellucida?

Answer 30

- 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.

Question 31

where does the blastocyst that has not yet implanted get its oxygen and metabolic subtrees required for growth and survival from?

Answer 31

the uterine secretions that it is bathed in

Question 32

what are the 3 stages of implantation in humans?

Answer 32

apposition attachment/adhesion invasion

Question 33

what are short range signals

Answer 33

oocyte, sperm, seminal plasma and embryo

Question 34

what are long range signals?

Answer 34

hormones, nutrition and environmental factors

Question 35

in humans where does the blastocyst usually implant?

Answer 35

posterior wall of the uterine fundus

Question 36

what happen during adherence in implantation?

Answer 36

trophoblast cells of the blastocyst adhere to the luminal epithelial cells of the endometrium.

Question 37

what has to happens before adhesion can occur?

Answer 37

the zona pellucida has to be removed.

Question 38

where do the enzymes required for the removal of the zona pellucida come from?

Answer 38

trophoblast cells themselves or the uterine secretions

Question 39

what does attachment induce changes in?

Answer 39

endometrial epithelium and the underlying endometrial stromal tissue (initiating its development as the maternal component of the placenta)

Question 40

different species have different types of implantation. | what are they two types of implantation?

Answer 40

invasive and non invasive

Question 41

which species does invasive implantation occur in?

Answer 41

humans, primates, dogs, cats, mice and rabbits. | the free living blastocyst of the species is relatively short lived

Question 42

which species does non invasive implantation occur in?

Answer 42

pig, sheep, cow and horse | attachment is initiated later than in invasive conception.

Question 43

when is hCG synthesised in the the trophoblast of the impacting blastocyst?

Answer 43

as early as 6-7 days after fertilisation.

Question 44

what is the role of pinipodes?

Answer 44

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)

Question 45

when does the receptive phase occur?

Answer 45

day 7 to 10 of menstrual cycle

Question 46

when is the endometrium said to be prereceptive?

Answer 46

days 1 to 7 of menstrual cycle

Question 47

which hormone domination is required if the uterus and implanting blastocyst are to engage effectively?

Answer 47

progesterone

Question 48

what are the molecular messages of attachment?

Answer 48

- 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.

Question 49

what is one of the key 'go away' messages provided by?

Answer 49

a glycoproteins called Muc1

Question 50

what is one of the key 'come hither' messages in attachment?

Answer 50

leukaemia inhibitory factor (LIF) --> a cytokine produced by the cells of the endometrial glands

Question 51

what does LIF do?

Answer 51

it permits the cells of the luminal epithelium to respond to local signals from activated blastocysts. (sensitises the epithelium to the blastocyst)

Question 52

what are molecular messages of invasion?

Answer 52

MMPs - metalloproteinases - digest stomal components | TIMPs - tissue inhibitors of MMPs - holds MMPs in check.

Question 53

why is decidualization response by stomal cells at implantation described as resembling a pro inflammatory endometrial reaction?

Answer 53

because prostaglandins which are key players in inflammatory responses are involved in implantation.

Question 54

what are some molecular messages of invasion other than MMps and TIMPs.

Answer 54

prostaglandins COX 2 vascular endothelial growth factor (VEGF) interleukin 11

Question 55

how long does the fetal phase last for

Answer 55

220 days

Question 56

what does oestrogen stimulate proliferation and differentiation of?

Answer 56

uterine epithelial cells

Question 57

what does progesterone stimulate proliferation and differentiation of?

Answer 57

stomal cells

Question 58

up until which point can progesterone receptor antagonists induce abortion?

Answer 58

7 weeks of gestation.

Question 59

when does the placenta take over the progesterone production?

Answer 59

approx 12 weeks.