4 Development Of Bilaminar And Trilaminar Germ Discs Flashcards
1
Q
Why is the amniotic cavity opened?
A
To examine dorsal side of epiblast
2
Q
True or false. The epiblast and hypoblast are not in contact with each other.
A
False. The hypoblast and epiblast are in contact with each other
3
Q
Layer of cuboidal cells adjacent to blastocyst cavity
A
Hypoblast
4
Q
Layer of columnar cells adjacent to amniotic cavity
A
Epiblast
5
Q
Amnioblasts
A
Epiblast cells adjacent to cytotrophoblasts
6
Q
Whats the structure that implanted in the uterine?
A
Blastocyst
7
Q
Whats the blastocyst composed of?
A
Inner cell mass that will develop into embryo and cyto and syncytiotrophoblast will give rise to supporting cells of embryo
8
Q
What will the trophoblast give rise to?
A
Future placenta
9
Q
When are the three germ layers formed?
A
During gastrulation
10
Q
What is the bilaminar disc mainly composed of ?
A
Epiblast and hypoblast
11
Q
Where does fertilization occur?
A
Ampulla of uterine tube / fallopian tube
12
Q
Where does implntation occur?
A
Body of uterus
13
Q
What part of the blastocyst will attach to the uterine wall?
A
The outer layer of the trophoblast
14
Q
When does cleavage of the zygote occur?
A
After fertilization
15
Q
Inner cell mass aka
A
Embryoblast
16
Q
Embryoblast pulls away from trophoblast and forms
A
Hollow amniotic cavity
17
Q
What happens in the 2nd week of development?
A
Trophoblast-> cyto + syncyto
Extraembryonic meso -> splanchnic + somatic
Embryoblast -> epi + hypo
2 cavities form -> amniotic + primary ys
18
Q
Hypoblast cells start to migrate and form
A
Primary yolk sac
19
Q
Part of the hypoblast will make
A
Extraembryonic mesoderm ( somatic pleura + splanchnic pleura)
20
Q
What happens at the end of the 2nd week?
A
Primitive streak appearance
21
Q
Functions of primitive streak
A
Marking early stages of gastrulation
22
Q
Where does primitive streak appear?
A
In caudomedial region of embryo
23
Q
Whats the source of the primitive streak?
A
Epiblast cells
24
Q
Whats the function of cavities?
A
Nourish the embryo
25
What does the extraembryonic mesoderm form?
Important in connecting stalk which will give rise to umbilical cord
26
Where does the primitive streak form a shallow groove?
In the caudal region of the germ disc
27
When does Formation of the primitive streak occur?
3rd week
28
Where does the primitive node appear?
at the cephalic end of the streak
29
When does Appearance of primitive node at the cephalic end of the streak occur?
3rd week
30
When does Migration of the epiblast cells toward the primitive streak occur?
3rd week
31
Where do epiblast cells migrate to?
Toward primitive streak
32
When does Detachment and invagination (ingression) of epiblast cells in the region of the
primitive streak occur?
3rd week
33
When does Formation of embryonic endoderm and the mesoderm from the migrating cells of
the epiblast occur?
3rd week
34
Formation of embryonic endoderm and the mesoderm from
the migrating cells of
the epiblast
35
When does Formation of the ectoderm from the remaining cells of the epiblast occur?
3rd week
36
Formation of the ectoderm from the
remaining cells of the epiblast
37
Main events during third week of development:
Gastrulation and formation of trilaminar germ disc
38
Gastrulation and formation of trilaminar germ disc step by step
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
39
Orophrangyeal membrane is very early evidence of what?
Our mouth
40
Cloacal membrane is early evidence of what?
Of the anus
41
Prenotochordal cells
Will migrate to cephalic region and give rise to notochord
42
Which side of the embryo will develop first?
The left side
43
Where will the primitive node appear?
At cephalic end of primitive streak
44
Function of primitive node
Organizes migration of epiblast cells to form three germ layers
Ensured what transcription factors or genes are expressed at what time ( ensure gastrulation)
45
When does formation of notochord happen?
Day 17
46
Cells that will make up the notochord are ..
Very close to the primitive streak
47
Function of notochord
Axis for development
48
Source of notochord
Mesoderm cells that attach to endoderm ( forming notochordal plate) then detach from it
49
What are the two main types of mesoderms?
Extraembryonic and intraembryonic
50
The intraembryonic mesoderm will further differentiate into
Paraxial lateral and intermediate mesoderms
51
Paraxial mesoderm will give rise to
Somites that develop into muscles and bones
52
When does Establishment of the body axes occur?
Week 2 and 3
53
What must happen in order for Establishment of the body axes to occur?
Notochord must form
54
The notochord will regulate gene expressions and transcription factors to ensure that development occurs _________ and __________
Cephalocaudally and left to right
55
Up and down
Dorsal and ventral
56
North east and south west
Right and left
57
Left and right
Cranial and caudal
58
The anteroposterior axis is signaled by cells at
anterior (cranial) margin of the embryonic disc, the Anterior Visceral Endoderm (AVE)
59
Cells in the AVE express genes essential for … and secreted factors cerebrus …
for head formation
contribute to head development and establish the cephalic region.
60
• Cells in the AVE express genes essential for head formation, including
the transcription factors OTX2, LIM1, and HESX1
61
What secreted factors contribute to head development and establish the cephalic region?
Cerebrus
62
What happens once the streak is formed and gastrulation is progressing?
BMP4 is secreted throughout the bilaminar disc and acts with FGF to ventralize mesoderm into intermediate and lateral plate mesoderm
63
Where is goosecoid expressed?
In the node
64
Goosecoid function
regulates chordin expression,
65
What is Goosecoid?
Gene product
66
Function of goosecoid together with noggin and follistatin?
inhibits the activity of BMP4, dorsalizing mesoderm into notochord and paraxial mesoderm for the head region.
67
expression of the Brachyury (T) gene antagonizes BMP4 to do what?
to dorsalize mesoderm into notochord and paraxial mesoderm in caudal region of the embryo.
68
What antagonizes BMP4?
Brachyury (T) gene
69
What genes are important in head formation?
OTX2, LIM1 , HESX1, secreted factor cerebrus
70
What will activating BMP4 with FGF result in?
Ventralizing ( lateral and intermediate)
71
What will blocking BMP4 and FGF ( using goosecoid , noggin and follistatin together) result in?
Dorsalizing ( paraxial mesoderm and notochord.)
72
Why was goosecoid used to dorsalize the embryo/ whats the purpose of dorsalizing the embryo?
So that the notochord is positioned in the back of the baby not the stomach
73
_____secreted by the node and primitive streak, establishes ______,
FGF8
Nodal
74
What secretes FGF8?
Node and primitive streak
75
FGF8 secreted by the node and primitive streak, establishes Nodal and then nodal proteins …
accumulates on the left side of
the node.
76
What is Nodal?
a member of TGF-β superfamily
77
Why are they called “LEFTY-1” and “ LEFTY-2” ?
Because they can only be found on the left side
78
As the neural plate starts to form, neurotransmitter serotonin (5HT)
increases in concentration on the left side
79
As the neural plate starts to form, neurotransmitter serotonin (5HT) increases in concentration on the left side. Why?
because of its metabolism by MAO on the right.
80
What happens under the influence of 5HT?
FGF8 induces expression of Nodal and LEFTY-2 in the lateral
plate mesoderm, whereas LEFTY-1 is expressed on left side of the ventral aspect of the neural tube
81
What also participates in induction of Nodal, LEFTY-1, and LEFTY-2?
Products of Brachyury (T), expressed in the notochord
82
Expression of Nodal and LEFTY-2 regulates…
expression of the transcription factor PITX 2, which, through further downstream effectors, establishes left-sidedness.
83
What establishes left sidedness through further downstream effectors?
PITX2
84
where is SHH expressed?
In the notochord
85
SHH possibly serves as a
as a midline barrier and also represses expression of left-sided genes on the right.
86
Expression of the transcription factor Snail may regulate
downstream genes important for establishing right-sidedness.
87
What germ layer is the nervous system derived from?
Ectoderm
88
What germ layer is the sensory epithelium of eye , ear, nose derived from?
Ectoderm
89
What germ layer is the epidermis , haur, and nails derived from?
Ectoderm
90
What germ layer is the mammary and cutaneous glands derived from?
Ectoderm
91
What germ layer is the epithelium of sinuses oral and nasal cavities , intraoral glands derived from?
Ectoderm
92
What germ layer is the tooth enamel derived from?
Ectoderm
93
What germ layer are the muscles derived from?
Mesoderm
94
What germ layer are the CT derivatives : bone cartilage, blood,dentin, pulp, cementum, periodontal ligament derived from?
Mesoderm
95
In reference of the notochord whats the most lateral epiblast cell going to give rise to?
Extraembryonic mesoderm
96
In reference of the notochord whats the most medial epiblast cell going to give rise to?
Paraxial mesoderm
97
In reference to notochord list the fate map of the epiblast cells from most medially to most laterally.
Paraxial mesoderm
Intermediate mesoderm
Lateral plate mesoderm
Extraembryonic mesoderm
98
What germ layer are the GI tract epithelium and associated glands derived from?
Endoderm
99
Malformation of head region
Can be duplication, malformation, or conjoined twins
100
Cause of malformation of head region
Over / under expression of goosecoid which activates BMP4 inhibtors
101
Malformation of lumbosacral region 2 egs
Sirenomelia ( caudal disgenesis) and sacrococcygeal teratoma
102
Range of defects of sirenomelia
Hypoplasia
Fusion of lower limbs
Vertebral abnormalities
Renal agenesis
Anomalies of genital organs and imperforate anus
103
Cause of sirenomelia
Insufficient mesoderm formation in caudomost region of embryo/ loss of mesoderm in lumbosacral region
104
What is associated with sirenomelia?
Maternal diabetes
105
Sacrococcygeal teratoma
Tumors may become malignant and are most common in female fetuses
106
Cause of sacrococcygeal teratoma
Reminants of primitive streak that remained in sacrococcygeal region will become clusters of pluripotent cells that divide and form and result in sacrococcygeal teratom
107
Failure of establishment of normal L-R asymmetry ( situs inversus)
Failure to properly establish L-R axis
108
Situs solitus
Normal positioning of internal organs
109
What is important for establishing laterality?
Neurotransmitter serotonin (5HT)
110
What do laterality defects cause?
Complete reversal of organs
