6. Embryology Flashcards
(63 cards)
1
Q
how does one cell become a multicellular body?
A
- growth
- morphogenesis
- differentiation
2
Q
What is morphogenesis?
A
development of form and structure
3
Q
What is differentiation?
A
specialisation for function
4
Q
During weeks 1 -2 what is the stage called?
A
Pre embryonic
5
Q
During weeeks 3-8 what is the stage called?
A
Embryonic
6
Q
During weeks 9-38 what is the stage called?
A
Fetal
7
Q
When are pregnancies dated from?
A
• Pregnancies are dated from the first day after the last menstrual period and fertilisation is assumed to be at 2 weeks after that date
8
Q
What happens during fertilisation?
A
- Oocyte is released from the ovary
- Travels along the Fallopian (uterine) tube
- Is fertilised by sperm in the ampulla
- Fertilised oocyte is called the zygote
9
Q
What is the ideal site for implantation ?
A
Ideal site for implantation is the posterior uterine wall
10
Q
What 4 things happen during week one of the pre-embryonic period?
A
- Cleavage
- Compaction
- Hatching
- Implantation begins
11
Q
What happens during cleavage?
A
- Cleavage - splitting - first mitosis division
• results in 2 blastomeres of equal size
• Mitosis continues until a morula is formed
12
Q
What is the zone pellucida?
A
The glycoprotein shell that surrounded the ovum and ensures only one sperm gets in
13
Q
What stage of differentiation are the cells of the morula?
A
Totipotent
14
Q
What happens during compaction?
A
formation of the first cavity - blastocyst cavity — fluid filled space
The whole structure is now called the blastocyst
15
Q
What happens during hatching?
A
- blastocyst hatches from zona pellucida
- no longer constrained - now free to enlarge
- can now interact with uterine surface to implant
16
Q
What two things are occurring at the same time during the pre embryonic stage?
A
- Making an embryo
2. Making a placenta to support the embryo
17
Q
At the very early stages formation of what has priority?
A
Placenta
18
Q
What does Totipotent mean?
A
The capacity to become ANY cell type
19
Q
What does pluripotent mean?
A
The capacity to become one of MANY cell types - not placenta
20
Q
Before compaction are the cells Totipotent or pluripotent?
A
Totipotent
21
Q
After compaction, are the cells Totipotent or pluripotent?
A
Pluripotent
22
Q
What happens during assisted reproductive techniques?
A
- Oocytes are fertilised in vitro and allowed to divide to the 4- or 8- cell stage
- The morula is then transferred into the uterus
23
Q
What structures are present in the blastocyst?
A
- Embryoblast (inner cell mass): which forms the embryo
- Trophoblast (outer cell mass): forms supporting tissue for embryo
- Blastocoele (blastocyst cavity): first cavity formed
24
Q
What happens during week 2 of the pre embryonic period?
A
- Differentiation
- Implantation complete
- rapid development of syncytiotrophoblast at embryonic pole
- Primitive yolk sac formation
- primitive yolk sac membrane is pushed away from cytotrophoblast layer
- Maternal sinusoids invaded by syncytiotrophoblast
- Formation of secondary yolk sac
- Spaces within the extraembryonic mesoderm merge to form the chorionic cavity
25
What happens during differentiation?
two distinct cellular layers emerge from:
>outer cell mass
• syncytiotrophoblast
• cytotrophoblast
>inner cell mass becomes the bilaminar disk
• epiblast
• hypoblast
26
What happens during completion of implantation?
• implantation is interstitial
>the uterine epithelium is breached and the conceptus implants within the uterine stroma
• establishes maternal blood flow within the placenta
> Allows support of the embryo from maternal circulation
•establishes the basic structural unit of materno-fetal exchange
>The chorionic villus
27
What happens during week 2 day 9?
```
• Embryonic pole
>rapid development of
syncytiotrophoblast
• Abembryonic pole
>Primitive yolk sac formed
```
• Yolk sac membrane in contact
with cytotrophoblast layer
28
What happens during week 2 day 11?
```
• primitive yolk sac membrane is
pushed away from
cytotrophoblast layer by an
acellular extraembryonic
reticulum
• reticulum later converted to
extraembryonic mesoderm by
cell migration
```
29
What happens during week 2 day 12?
```
• Maternal sinusoids invaded by
syncytiotrophoblast
• lacunae become continuous with
sinusoids
• uteroplacental circulation
begins
• uterine stroma prepares for
support of the embryo
```
30
What happens during week 2, day 13?
* Formation of secondary yolk sac
* a.k.a. definitive yolk sac
* pinches off from primitive yolk sac
31
What happens during week 2 say 14?
```
• Spaces within the extraembryonic
mesoderm merge to form the chorionic
cavity
• The embryo and its cavities are
suspended by the connecting stalk
> column of mesoderm
> future umbilical cord
• Bleeding around now can be confused
with menstrual bleeding
```
32
What is a blastocoele?
first cavity, formed as a result of compaction
33
What is the amniotic sac?
formed from spaces within the epiblast
34
What is the primitive yolk sac?
* a.k.a exocoelomic cavity
| * formed by hypoblast lining blastocoele
35
What is the secondary yolk sac?
* a.k.a definitive yolk sac
| * formed within primitive YS
36
What is the Extraembryonic coelom?
* a.k.a chorionic cavity
| * formed from spaces within extraembryonic reticulum & mesoderm
37
What are two implantation defects?
Ectopic pregnancy
| Placenta praevia
38
What is ectopic pregnancy?
> implantation at site other than uterine body
(Most commonly Fallopian tube)
> Can be peritoneal or ovarian
> can very quickly become life threatening emergency
39
What is placenta praevia?
> implantation in the lower uterine segment
> can cause haemorrhage in pregnancy
> requires c section delivery
40
Which period is the period of greatest change?
Embryonic period
41
At which period is there the greatest risk of major congenital malformation (i.e. teratogenesis) due to
environmental exposure or drug
therapy?
Embryonic period
42
In general, what happens during the early embryonic period?
Foundations laid for the development of the body systems
43
What are Key events and processes in early development?
1. fertilisation & implantation
2. gastrulation
3. neurulation
4. segmentation
5. folding
44
At the end of the second week the epiblast is a?
Uniform disc
45
In the third week, what is the new feature that appears on the dorsal surface of the epiblast?
primitive streak
46
What does the primitive streak indicate?
That gastrulation is going to start
47
What is the head end (away from edge of the disk )of the primitive streak called?
Primitive node
- Within the primitive streak lies a primitive node at the cranial end, and within the primitive node lies the primitive pit.
48
When does gastrulation occur?
in the third week of development, marking
| the start of the embryonic period
49
Why does gastrulation occur?
Prior to gastrulation the embryonic disk
| is bilaterally symmetrical
50
Describe what happens during gastrulation
• primitive streak forms in the caudal epiblast,
leading to migration & invagination of epiblast cells.
• The hypoblast is responsible for establishing a primitive yolk space - so it is displaced and degenerates and then the 3rd layer is created
• the bilaminar disk is converted to a trilaminar disk
51
What does the ectoderm become?
organs & structures that maintain contact with outside world
e.g. nervous system, epidermis
52
What does the mesoderm become?
supporting tissues
| e.g. muscle, cartilage, bone, vascular system (including heart & vessels)
53
What does the endoderm become?
internal structures
| e.g. epithelial lining of GI tract, respiratory tract; parenchyma of glands
54
What is situs inversus?
complete mirror-image viscera
55
What is the viscera?
the internal organs in the main cavities of the body, especially those in the abdomen, e.g. the intestines.
56
What causes situs inversus?
commonly results from immotile cilia
57
What are the associated morbidities of situs inversus?
no associated morbidity (usually)
58
When do problems arise in individuals with situs inversus ?
problems arise if there is both normal and
| mirror-image disposition
59
What is the shape of the embryonic disk prior to gastrulation/
Prior to gastrulation the embryonic disk
| is bilaterally symmetrical
60
How do we go from a bilaterally symmetrical embryonic disk to having left and right differences?
Action of ciliates cells at the primitive node results in left wards flow of signalling molecules for left side and right wards flow of signalling molecules for right side
61
What is the notochord?
Solid rod of cells running in the midline(middle of mesoderm) with important signalling role.
62
How is the neuroectoderm created?
Notochord Releases signalling molecules which diffuse and act on cells in the ectoderm.
Notochord directs conversion of overlying ectoderm to
NEURECTODERM
63
How is the neural tube created?
• Notochord signals cause overlying ectoderm to thicken
• Slipper-shaped neural plate
• Edges elevate out of the plane of the disk and curl towards each other, creating
the neural tube
