L4: Development Of Bi & Trilaminar Germ Discs Flashcards
1
Q
What is the egg form that would be implanted?
A
• Blastocyst with an inner and outer cell mass
2
Q
where does the implantation take place?
A
In the wall of the uterus > endometrium
3
Q
Where does fertilization take place?
A
In the fallopian tube ampulla
4
Q
What is the formation of ectoderm, endoderm and mesoderm process called?
A
Gastrulation
5
Q
Notochord establishes what?
A
establish body axis
6
Q
The blastocyst is composed of two main components: which are
A
o the outer cell mass > the trophoblast
o the inner cell mass > the embryoblast.
7
Q
Which part of the blastocyst Will Connect to the endometrium?
A
trophoblast
8
Q
When does the trophoblast differentiate into two layers?
A
After the contact with the endometrium
9
Q
What will happen to the blastocyst outer cell mass (trophoblast)?
A
trophoblast will differentiates them to two layers
10
Q
the trophoblast will differentiate into what?
A
- the cytotrophoblast
- the syncytiotrophoblast
11
Q
what is the cytotrophoblast?
A
- an inner layer of mononucleated cells
- in contact with the embryo
- villi for circulation
- source of syncytiotrophoblast
- when it extend in the endometrium
12
Q
what is synchytiotrophoblast?
A
- an outer multinucleated zone without distinct cell boundaries, (these contribute to the formation of the placenta (Direct to the endometrium))
- produce human chorionic gonadotropin (hCG)
- important for the corpus luteum
- maintain pregnancy
13
Q
What will happen to the blastocyst inner cell mass > the embryoblast?
A
- the Hypoblast > a layer of cuboidal cells adjacent to the blastocyst cavity
- the Epiblast > a layer of columnar cells adjacent to the amniotic cavity
14
Q
What forms the bilaminar germ disc?
A
Hypoblast and Epiblast
15
Q
How is the amniotic cavity formed?
A
Embryoblast pulls away from the trophoblast forming a hollow Amniotic Cavity.
16
Q
Describe the location of the Amniotic cavity?
A
- It appears between the epiblast and cytotrophoblast
* Important for nourishment
17
Q
Define amnioblasts cells?
A
They are the Epiblast cells adjacent to the cytotrophoblast.
18
Q
What makes the extraembryonic mesoderm?
A
Hypoblast cells migrate
19
Q
What does the extraembryonic mesoderm split to?
A
- Extraembryonic somatic mesoderm
* Extraembryonic splanchnic mesoderm
20
Q
Extraembryonic somatic mesoderm is
A
The mesoderm of the amnion and chorion
21
Q
Extraembryonic splanchnic mesoderm is
A
The mesoderm of the yolk sac and
allantois > in close contact with cytotrophoblast > makes the Primary yolk sac
22
Q
What is the exocoelomic sac?
A
Remains of the space of the extraembryonic membrane > disappear
23
Q
Why is 2nd week of development is called the week of 2’s?
A
- The trophoblast differentiates into 2 layers > cytotrophoblast+ syncytiotrophoblast
- The embryoblast forms 2 layers > Hypoblast+ the Epiblast
- the extraembryonic mesoderm splits into 2 layers > somatic and splanchnic
- Two cavities formà chorionic + Amniotic cavity
24
Q
where does the amniotic fluid develops?
A
dorsal to the epiblast.
25
where does the primary yolk sac develops?
ventral to the hypoblast.
26
where does the chronic cavity develops?
between Heuser's membrane (the exocoelomic membrane) and
| the trophoblast.
27
What do epithelial cells convert to?
convert to mesenchymal cells
28
mesenchymal cells have the ability to...
migrate from the cephalic to the caudal region
29
What happens at the end of the 2nd week of development?
* The amniotic cavity is opened to examine the dorsal side of the epiblast
* The hypoblast and epiblast are in contact with each other
* The primitive streak forms a shallow groove in the caudal region of the germ disc
30
How are the epiblast cells migrating?
By invagination
31
What marks the beginning of gastrulation?
the appearance of a groove in the caudal end of the epiblast layer known as the primitive streak.
32
What is the most important Event during third week of development?
Gastrulation and formation of trilaminar germ disc
33
What are the other events in the 3rd week
* Formation of the primitive streak
* Appearance of primitive node at the cephalic end of the streak
* Migration of the epiblast cells toward the primitive streak
• Detachment and invagination (ingression) of epiblast cells in the region of the primitive
streak
• Formation of embryonic endoderm and the mesoderm from the migrating cells of the
epiblast
• Formation of the ectoderm from the remaining cells of the epiblast
34
How is endoderm made?
By replacing the hypoblast with epiblast
35
When is the notochord Formed?
• day 17
36
how is the notochord formed?
First epiblast migrates to the mesoderm, touch the endoderm then the cells detach from the endoderm and be in the mesoderm
37
The notochord is derived from
mesoderm
38
when is the body axes Established?
weeks 2 & 3 by the notochord
39
How is the anteroposterior axis is signaled?
by cells at the anterior(endoderm) (cranial) margin of the embryonic disc, the Anterior Visceral Endoderm (AVE).
40
what is the importance of the AVE?
• it express genes essential for head formation,
• the secreted factors cerberus that contribute to head development and establish the
cephalic region.
41
what are the TF of AVE?
- OTX2
- LIM1
- HESX1
42
When is BMP4 is secreted?
Once the streak is formed and gastrulation is progressing.
43
What secretes BMP4?
is secreted throughout the bilaminar disc
44
what is BMP4 role?
acts with FGF to ventralize mesoderm into intermediate and lateral plate mesoderm.
45
Where is Goosecoid expressed?
in the node
46
what is Goosecoid role?
regulates chordin expression
47
what inhibits the activity of BMP4?
goosecoid + noggin and follistatin
48
what does the inhibition of BMP4 leads to
leads to dorsalizing mesoderm into notochord and paraxial mesoderm for the head region.
49
When the Brachyury (T) expressed?
After the dorsalizing the Brachyury (T) gene is expressed
50
What is the role of Brachyury (T)?
Brachyury (T) gene antagonizes BMP4 to dorsalize mesoderm into notochord and paraxial mesoderm in caudal region of the embryo.
51
How is FGF8 secreted?
by the node and primitive streak
52
what is the role of FGF8?
establishes Nodal, a member of TGF-β superfamily, and the nodal protein then accumulates on the left side of the node.
53
which side is formed first?
Accumulation on the left side more than the right side > formation of the left side first
54
When does neurotransmitter serotonin (5HT) increases in concentration?
as the neural plate starts to form
55
on which side do we find 5HT increase?
neurotransmitter serotonin (5HT) increases in concentration on the left side
56
why does the increase of 5HT happens on the left side?
Because of its metabolism by MAO on the right.
57
What induceses the expression of FGF8 of Nodal?
under the influence of 5HT
58
FGF8 induces expression of....
Nodal and LEFTY-2
59
where does the FG8 induces expression of nodal & lefty-2?
in the lateral plate mesoderm
60
where is lefty-2 expressed?
on left side of the ventral aspect of the neural tube.
61
What is the role Brachyury (T) in this proses?
products of Brachyury (T)(expressed in the notochord) also participate in induction of
these three genes.
62
What is the effect of the Expression of Nodal and LEFTY-2
It regulates the expression of the transcription factor PITX 2
63
What is the role of factor PITX 2?
which, through further downstream effectors, establishes left-sidedness.
64
Where is SHH expressed?
in the notochord
65
What is the role of factor SHH?
* possibly serves as a midline barrier
| * represses the expression of left-sided genes on the right.
66
What is the role of transcription factor Snail?
• Expression of the transcription factor Snail may regulate downstream genes important for
establishing right-sidedness.
67
What are the derivatives of the ectoderm?
1. Nervous system
2. sensory epithelium of ear nose
3. Epidermidis hair nails
4. Mammary and cutaneous clans
5. epithelium of sinuses, oral, and nasal cavities, intraoral glands
6. tooth enamel
68
What are the derivatives of the mesoderm?
```
• Muscles
• CT derivatives:
1. Bone
2. Cartilage
3. Blood
4. Dentin
5. pulp
6. cementum
7. periodontal ligament
```
69
What are the derivatives of the endoderm?
• G.I. tract epithelium and associated glandes
70
what could cause Malformation of the head region ?
Over- or under expression of Goosecoid
why? Because it activates inhibitors of BMP4
71
What are the possible malformations of the head caused by Over- or under expression of
Goosecoid ?
• Several malformation including duplications, similar to some types of conjoined
twins.
72
what are the two examples of malformation of the lumbosacral region
- sirenomelia (caudal dysgensis)
| - sacrococcygeal teratoma
73
Example of malformation of the lumbosacral region?
1. hypoplasia
2. fusion of lower limbs
3. vertebral abnormalities
4. renal agenesis
5. anomalies of the genital organs and imperforate anus
6. Maternal diabetes and other causes are associated with this condition.
74
What is the possible cause for Sacrococcygeal teratoma?
Probably results from remnants of the primitive streak.
75
Sacrococcygeal teratoma is most common in..
in female fetuses (These tumors may become malignant)
76
who is a risk factor of sirenomelia?
maternal diabetes
77
What is an example of the Failure of establishment of normal left-right asymmetry?
- Situs inversus > it is rare
| - Express in the right side before the left side > heart problems
78
lateral defect causes what?
complete reversal of organs
