week 4 - implantation and pregnancy Flashcards
1
Q
when cyte is used at the end of a germ cell what does it mean? e.g. oocyte
A
haploid
in meiosis
2
Q
when gonia is used at the end of a germ cell what does it mean? e.g. spermatogonia
A
diploid
3
Q
At the zygote / ovum what can you see in the cell? (4)
A
Male and female pronuclei that havent fused yet
zona pelucida
cumulus cells
second polar body
4
Q
When do male and female pro nuclei fuse? and what is the cell termed after they have fused?
A
syngamy
proper diploid cell
5
Q
what is the zona pelucida?
A
it is what the sperm makes its way through and hardens afterwards
fuzzy gelatinous layer
6
Q
You can see how many polar bodies at any one time in an ovum?
A
only ever one polar body
7
Q
when the pro nuclei fuse the cell conceptus goes 2 cells, 4 cells, 8 cells, but the zona pelucida is still there so what occurs?
A
it cant grow
it means when the cells divide they are all small because the whole thing is constrained by the ZP, unless the ZP starts to thin and stretch the cells are confined
8
Q
What is the morula?
A
ball of 16 cells
the ZP starts to thin and so growth can occur
9
Q
what sort of growth occurs to the morula?
A
embryonic growth - giving rise to an embryo
10
Q
within the morula the individual cells are termed what?
A
blastomere
11
Q
every blastomere inside the morula is _____
A
totipotent - it can become anything
12
Q
define pluripotent
A
cell has the potential to become one of several things
13
Q
what happens when a totipotent cell is removed?
A
any other totipotent cell can replace it so offspring dont appear to be affected
14
Q
what is the function of the ZP?
A
hardens and prevents polyspermy
keeps cells together
plays a crucial role in preventing chimeric embryos
15
Q
what would happen if you have several embryos (polytocus mammal) and didnt have a zona pelucida around each one?
A
they would stick and fuse
the blastomeres from one embryo would transfer to another
this is demonstrated in mice in the lab where they exchange blastomeres during embryogenesis
16
Q
when does the blastomere become a blastocyst?
A
when a cavity opens up in the middle of the morula due to geometry calculations and the sphere is getting larger at a faster rate than the exponential series of cells dividing
17
Q
the cavity that opens up in the blastocyst is called ____
A
blastocoel
18
Q
The blastocyst is the first time you see ___ between the cells
A
differentiation
19
Q
what are the cells around the outside of the blastocyst called?
A
trophoblast
20
Q
as well as the trophoblast and blastocoel there is one other structure in the blastocyst, what is it and what is its purpose?
A
pluriblast or inner cell mass (ICM)
goes onto make the embryo
21
Q
what does the trophoplast do in the blastocyst?
A
contributes to the placenta
22
Q
the blastocyst is a morula with individual blastomeres that are all ____
A
totipotent
23
Q
Blastocyst derivatives
Trophoblast can be divided into ___ and ____, which contribute to the chorion
The pluriblast can be divided into ___ and ____.
The ____ goes onto form the yolk sac and the ___ will give us the various layers of the endoderm (___,___,___)
So why shouldnt you refer to a blastocyst as an embryo?
A
cytotrophoblast and syncyiotrophoblast
hypoblast and epiblast
hypoblst
epiblast
endoderm, mesoderm, ectoderm
Because the fetus is only a small portion of the blastocyst not all of it.
24
Q
why does the blastocyst have to hatch?
A
— make its way out of the zona pelucida in order to divide —–needs to come out of the ZP to expose its surface in order to be able to attach to the endometrium
25
when the embryo attaches to the endometrium at which stage is the process irreversible?
adhesion
26
what are the 2 phases of embryo attachment?
apposition
| adhesion
27
what is apposition?
when the embryo just touches the endometrium.
| this process is reversible
28
what is adhesion?
the embryo is bound to the endometrium and depending on the species it may be invasion
29
the molecular mechanisms involved in apposition and adherence of embryos differ between ______ and include redundancy
differ between species
30
what is redundancy in terms of apposition and adhesion?
several molecules fulfil the same functions
31
if you see redundancy occurring what does it tell you?
that process is so important that it cant afford to go wrong
32
There are proteins and glycoproteins that are covering the endometrium and they can do 2 things?
attract an embryo
| repel an embryo
33
The first thing you need to do in an embryo attachment is to get rid of anything that would block or deter an embryo.........
need to down regulate endometrial molecules which would block / deter adherence -- MUC1
34
MUC1 is an o linked glycoprotein that is upregulated by ____ and down regulated by ____
progesterone - puts more MUC1 on the endometrium
| blastocyst - when the blastocyst arrives it gets rid of MUC1
35
You also need to before embryo attachment get more molecules that will attract the embryo.......
upregulate molecules which facilitate adherence to the endometrium such as LIF1
36
Estrogen induced ___ with paracrine roles in:
- ---____ of endometrium
- ---up regulation of _______ ____
cytokine
decidualisation
EGF family (epidermal growth factor)
37
what is decidualisation?
changes in the endometrium to make it ready for the embryo
38
how does the ZP dissolve?
EGF family members include heparin binding EGF like growth factor, which activates EGF receptors plus heparan sulphate glycoproteins (HSPG) on the trophoblast to dissolve the ZP
39
due to redundancy there are many other proteins implicated in embryo apposition including (5)
```
integrins
selectins
ECM molecules (extra cellular matrix)
trophinin bystatin tastin complex
frizzled notch interactions
```
40
between ungulates and rodents/lagomorphs/primates the major difference in timing of embryonic events in days post ovulation is in the ____
blastocyst attachment where it can take anywhere between 2-6 weeks for the embryo to attach. it is free floating in the uterine cavity.
41
the biggest challenge faced by the embryo in ungulates is?
nourishment as it is free floating for up to 6 weeks in the uterine cavity. where does it get its nourishment from
42
embryo implantation can be 2 types -
invasive
| non - invasive
43
what is invasive embryo implantation?
breach endometrial epithelium to invade the underlying stroma - e.g. primates, carnivores, rodents
44
what is non invasive embryo implantation?
endometrium or epithelium intact or locally disrupted, embryo stays on the surface of the uterus - e.g. ungulates
45
in non invasive implantation the blastocyst grows rapidly, but which part and why?
the blastocyst has 2 cell populations there is the trophoblast the cells around the outside that grow quickly and this is all about providing the maximum surface area because its for maximum absorption of nutrients
46
in non invasive implantation the embryos dont go through the epithelium they sit on the surface how?
on the embryo cotyledon and on the endometrium caruncle
| caruncle - cotyledon sit together but never breach each other
47
in invasive implantation the blastocyst implants while _____ and the trophoblast invades between epithelium and underlying ____
small
| stroma
48
when the trophoblast is invading the stroma undergoes decidualisation reaction and the quality of this response determines what?
how far the embryo invades
depth of invasion limited by speed of stromal / decidual response
poor decidiual response = deeper invasion
49
on the trophoblast cells what attach it to the endometrium?
the villi
50
if there is no ZP around the trophoblast then what would happen?
you would get an eptopic pregnancy as the villi of the trophoblast cells would attach to anywhere
51
invasive implantation appears to be an ____ cascade
inflammatory
52
for the inflammatroy cascade we need up regulation of _____ and simultaneously of ____
MMP's - enzymes that will break down the extracelllular matrix
TIMP's - tissue inhibitors of metaloproteanases
need timps simultaneously because need to confine the MMPs so they dont break down extracellular matrix of everythign
53
what is good evidence that the inflammatory cascade is required for implantation?
if we were to cause inflammation of the endometrium by scratching the endometrium the women who have had miscarriages the chance of an embryo sticking increases massively so clearly there is a problem with their inflammatory response and you need to induce it prior to the embryo trying to implant
54
what is the mothers contribution to the placenta?
she provides the decidulate
55
what is decidualisation in detail? (4)
rapid changes in the endometrial stroma underlying the conceptus including:
- --increased vascular permeability
- --oedema
- -loosening of the ECM between cells
- -stromal cell differentiation
56
Decidualisation looks to be an inflammatory cascade mediated by: (5)
```
increased prostaglandins
pro-inflammatory cytokines
VEGFs
angiopoiteins
proliferin
```
57
implantation and decidualisation is an inflammatory response and we need to make sure it doesnt go too far so you do what?
```
produce something (cortisol?) which will stop the inflammation before it goes too far
upregulation of an enzyme which generates active cortisol from inert cortisone
```
58
in rodents decidualisation is _____
induced by presene of embryo
59
in rodents there are what sort of decidualisation reactions?
primary (local) followed by secondary (widespread)
60
placental classification is based on the shape of placenta, what are the 4 types?
discoid
zonary
cotyledonary
diffuse
61
explain discoid placenta
distinct disc on a particular region on the implanting blastomyst that will become the placenta
62
examples of animals with a discoid placenta
primates, lagomorphs, rodents
63
explain zonary placenta
placenta in a discrete zone on the blastomyst it is a ring
64
examples of zonary placenta
carnivores and seals and elephants
65
explain cotyledonary placenta
it is not a single structure (be that a disk or zone) but there are lots of little points of contact between the trophoblast (cotyledons) and specific points on the endometrium (coruncles)
66
example of cotyledonary placenta
sheep cow giraffe deer and goat
67
explain diffuse placenta
general contact between the embryo and endometrium - light contact which is easily broken in many places
68
example of diffuse placenta
lorises lemurs pig horse
69
Another way of defining the placenta is based on which type of maternal tissue the embryo is in contact with (4)
blood
capillary endotheium
endometrial endothelium
epithelial syncytium
70
explain a blood placenta with examples
the maternal tissue that contacts the foetal tissue is blood
| primates and rodents -HAEMOCHORIAL
71
explain a capillary endothelium placenta with examples
carnivores
zonary placenta contacts the endothelium cells from mums capillaries between her blood flow and the foetal blood flow
ENDOTHELIOCHORIO
72
explain an endometrial epithelium with examples
sheep and cow
non invasive implantation
foetal tissue are not in touch with blood vessels or blood but the endometrium epithelium
EPITHELIOCHORIAL
73
explain an epithelial syncytium with examples
pigs and horses
rather than contacting the epithelium there are a special set of cells between mothers epithelium and binutriate cells which are special cells from the foetus and they fuse to form a syncytium
SYNEPITHELIOCHORIAL
74
can also classify placenta based on the number of layers in the chorionic trophoblast (3)
one two or three
75
explain the 5 full types of placenta
haemomonochorial
haemodichorial
haemotrichorial
diffuse epitheliochorial
cotyledonary synepitheliochorial
76
what are the 5 challenges faced by an embryo?
preventing the demise of the corpus luteum (CL)
growth and development
nutrition
gaseous exchange
elimination of waste
77
why must the embryo prevent the demise of the CL?
because when the CL stops producing progesterone the endometrium will be shed and youve just implanted in something that is going to be lost
78
what is luteolysis?
maternal recognition of pregnancy (MRP)
---rescuing the CL so it continues to produce progesterone
79
most mammals require the early embryo to produce or stimulate the production of (2)?
luteotrophin - soething that will keep the CL alive and stop it shrinking
anti luteolysin - something that prevents a luteolysin (something which will kill the CL)
80
chorionic gonadotrophin (CG) is produced where?
in the pre implantation trophoblast
81
in humans what is CG shortened to? and in monkeys?
hCG
| mCG
82
mCG and hCG are very similar in molecular structure to which hormone?
LH (luteinizing hormone)
83
MRP in primates - CG
hCG and mCG activate the same G protein coupled receptor as LH. The __ ___ is dependent on CL and with out it what happens?
corpus luteum
| dies
84
so to maintain the pregnancy in the early stages and prevent the demise of the CL what do we do?
stimulate the same receptor LHGCR and this will upregulate the same genes as LH does and will increase the output of steroid from that CL
85
what synthesises and secretes equine chorionic gonadotrophin? (eCG)
trophoblast in the endometrial cups - remember horse has a diffuse placenta
86
eCG mimics which hormone?
FSH
87
what does eCG do in addition to activating LHCGR?
it will also stimulate FSHR and stimulates more follicles to develop which make more CL.
This animal is already pregnant and yet the embryo is going to make more ovulations happen in order to form more CL to contribute progesterone for the embryo
88
Why is luteolysis well studied in ruminants?
big financial implications for farming
89
what is different with the death of the CL in ruminants?
doesnt happen just because the LH runs out
| there is an active destructional component that comes from the uterus to kill the CL - PF2alpha
90
so what is happening with the CL and uterus in ruminants?
CL makes oxytocin a protein that stimulates the production of the PGF2 alpha in the endometrium that will kill the CL.
In the case of pregnancy an embryonic calf or lamb will make interferon tau and this switches off the oxytocin receptor so the CL survives
91
how long is the CL needed during pregnancy?
varies with species
92
in humans without pregnancy the CL lasts how long?
2 weeks
93
if your menstrual cycle changes is it ovulation or the CL that changes?
ovulation
| the CL is always a fixed number of days
94
if a women conceives the CL will survive for how long?
9 months rescued by hCG
95
do we need the CL for the entire pregnancy?
no only 3 months after that progesterone comes from the placenta
96
why shouldnt you tell people you are pregnant before 12 weeks?
because prior to this you are functioning off the CL and at 12 weeks you test the placenta for the first time where a large number of pregnancies fail
97
what happens in the absence of conception in a dog?
| no embryo is produced what happens to the CL?
the sensible thing would be that the CL dies quickly and the dog comes back into heat again
dogs show this pattern regardless of whether they conceive, they have their CL for 60 days
there is no MRP
98
how does the CL impact the dogs LRS/LRO?
every time she ovulates and produces a CL there are 60 days when there are no more follicles developing even if she is not pregnant.
this reduces her fertility massively as it is wasted time
MRP increase your feritlity
99
What is the life of the CL in rats?
if they have not mated 2 days
if they are pregnant 22 days
if that female is mated but there is no pregnanacy the CL lasts for 12 days - pseudopregnancy
the rat when mated assumes she is pregnant and waits until 12 days to check
100
what are the challenges faced by the mother?
growth and development
nutrition
gaseous exchange
elimination of waste
all the same as the challenges faced by the embryo / foetus she just cant do anything about the CL
101
At any one time cells either proliferate or differentiate.
What is the cellular priority for the pre-implantation embryo?
What is the cellular priority for post implantation embryo?
proliferation - grow as fast as you can
differentiation
102
when is it an embryo until? when does it become a foetus?
its an embryo until all the tissues have differentiated but cant rush this differentiation as need to proliferate to be a certain size first
103
what is the cellular priority for the foetus?
proliferation - hyperplasia
104
prior to the establishment of the placenta embryonic nutrition is ____
histiotrophic
| tissue nutrition
105
where do the histiotrophic nutrients come from?
metabolising the decidual stromal cells - carbs lipids etc
glandular secretions
106
after establishment of the highly vascularised placenta embryo and fetal nutrition become ___
haemotrophic - blood derived nutrition
107
In the early stages of embryogenesis we get fusion of the yolk sac mesoderm and the chorion, this is when we form the first placenta called_____
choriovitelline --- yolk sac placenta
108
In most eutheria the choriovitelline is short lived and replaced by the _____
chorioallantoic
109
In metatheria the choriovitelline is the sole source of ____
nutrition
110
In lagomorphs what happens to the choriovitelline?
it doesnt get exhausted but plays a secondary role during the pregnancy
111
what is the chorioallantoic placenta?
this is the chorion and the allantois
112
what is the allantois?
a piece of the endoderm that comes away from the hind gut
113
the chorioallantoic placenta is where we get the major role in the ___
haemotrophic nutrition
114
the interface in the haemochorial placenta is formed by the ___
cytotrophoblast (CTB)
115
the CTB can fuse to give us _____
syncytiotrophoblast which then fuses with the extraembryonic mesoderm to form the chorion
116
the chorion is going to fold into villi into which will fold microvilli providing ______ to be bathed in blood if its a haemochorial placenta
maximum surface area
