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Embryology > 4 Development Of Bilaminar And Trilaminar Germ Discs > Flashcards

4 Development Of Bilaminar And Trilaminar Germ Discs Flashcards

1
Q

Why is the amniotic cavity opened?

A

To examine dorsal side of epiblast

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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

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3
Q

Layer of cuboidal cells adjacent to blastocyst cavity

A

Hypoblast

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4
Q

Layer of columnar cells adjacent to amniotic cavity

A

Epiblast

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5
Q

Amnioblasts

A

Epiblast cells adjacent to cytotrophoblasts

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6
Q

Whats the structure that implanted in the uterine?

A

Blastocyst

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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

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8
Q

What will the trophoblast give rise to?

A

Future placenta

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9
Q

When are the three germ layers formed?

A

During gastrulation

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10
Q

What is the bilaminar disc mainly composed of ?

A

Epiblast and hypoblast

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11
Q

Where does fertilization occur?

A

Ampulla of uterine tube / fallopian tube

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12
Q

Where does implntation occur?

A

Body of uterus

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13
Q

What part of the blastocyst will attach to the uterine wall?

A

The outer layer of the trophoblast

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14
Q

When does cleavage of the zygote occur?

A

After fertilization

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15
Q

Inner cell mass aka

A

Embryoblast

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16
Q

Embryoblast pulls away from trophoblast and forms

A

Hollow amniotic cavity

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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

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18
Q

Hypoblast cells start to migrate and form

A

Primary yolk sac

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19
Q

Part of the hypoblast will make

A

Extraembryonic mesoderm ( somatic pleura + splanchnic pleura)

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20
Q

What happens at the end of the 2nd week?

A

Primitive streak appearance

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21
Q

Functions of primitive streak

A

Marking early stages of gastrulation

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22
Q

Where does primitive streak appear?

A

In caudomedial region of embryo

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23
Q

Whats the source of the primitive streak?

A

Epiblast cells

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24
Q

Whats the function of cavities?

A

Nourish the embryo

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25
Q

What does the extraembryonic mesoderm form?

A

Important in connecting stalk which will give rise to umbilical cord

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26
Q

Where does the primitive streak form a shallow groove?

A

In the caudal region of the germ disc

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27
Q

When does Formation of the primitive streak occur?

A

3rd week

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28
Q

Where does the primitive node appear?

A

at the cephalic end of the streak

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29
Q

When does Appearance of primitive node at the cephalic end of the streak occur?

A

3rd week

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30
Q

When does Migration of the epiblast cells toward the primitive streak occur?

A

3rd week

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31
Q

Where do epiblast cells migrate to?

A

Toward primitive streak

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32
Q

When does Detachment and invagination (ingression) of epiblast cells in the region of the
primitive streak occur?

A

3rd week

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33
Q

When does Formation of embryonic endoderm and the mesoderm from the migrating cells of
the epiblast occur?

A

3rd week

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34
Q

Formation of embryonic endoderm and the mesoderm from

A

the migrating cells of
the epiblast

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35
Q

When does Formation of the ectoderm from the remaining cells of the epiblast occur?

A

3rd week

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36
Q

Formation of the ectoderm from the

A

remaining cells of the epiblast

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37
Q

Main events during third week of development:

A

Gastrulation and formation of trilaminar germ disc

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38
Q

Gastrulation and formation of trilaminar germ disc step by step

A

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

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39
Q

Orophrangyeal membrane is very early evidence of what?

A

Our mouth

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40
Q

Cloacal membrane is early evidence of what?

A

Of the anus

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41
Q

Prenotochordal cells

A

Will migrate to cephalic region and give rise to notochord

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42
Q

Which side of the embryo will develop first?

A

The left side

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43
Q

Where will the primitive node appear?

A

At cephalic end of primitive streak

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44
Q

Function of primitive node

A

Organizes migration of epiblast cells to form three germ layers

Ensured what transcription factors or genes are expressed at what time ( ensure gastrulation)

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45
Q

When does formation of notochord happen?

A

Day 17

46
Q

Cells that will make up the notochord are ..

A

Very close to the primitive streak

47
Q

Function of notochord

A

Axis for development

48
Q

Source of notochord

A

Mesoderm cells that attach to endoderm ( forming notochordal plate) then detach from it

49
Q

What are the two main types of mesoderms?

A

Extraembryonic and intraembryonic

50
Q

The intraembryonic mesoderm will further differentiate into

A

Paraxial lateral and intermediate mesoderms

51
Q

Paraxial mesoderm will give rise to

A

Somites that develop into muscles and bones

52
Q

When does Establishment of the body axes occur?

A

Week 2 and 3

53
Q

What must happen in order for Establishment of the body axes to occur?

A

Notochord must form

54
Q

The notochord will regulate gene expressions and transcription factors to ensure that development occurs _________ and __________

A

Cephalocaudally and left to right

55
Q

Up and down

A

Dorsal and ventral

56
Q

North east and south west

A

Right and left

57
Q

Left and right

A

Cranial and caudal

58
Q

The anteroposterior axis is signaled by cells at

A

anterior (cranial) margin of the embryonic disc, the Anterior Visceral Endoderm (AVE)

59
Q

Cells in the AVE express genes essential for … and secreted factors cerebrus …

A

for head formation

contribute to head development and establish the cephalic region.

60
Q

• Cells in the AVE express genes essential for head formation, including

A

the transcription factors OTX2, LIM1, and HESX1

61
Q

What secreted factors contribute to head development and establish the cephalic region?

A

Cerebrus

62
Q

What happens once the streak is formed and gastrulation is progressing?

A

BMP4 is secreted throughout the bilaminar disc and acts with FGF to ventralize mesoderm into intermediate and lateral plate mesoderm

63
Q

Where is goosecoid expressed?

A

In the node

64
Q

Goosecoid function

A

regulates chordin expression,

65
Q

What is Goosecoid?

A

Gene product

66
Q

Function of goosecoid together with noggin and follistatin?

A

inhibits the activity of BMP4, dorsalizing mesoderm into notochord and paraxial mesoderm for the head region.

67
Q

expression of the Brachyury (T) gene antagonizes BMP4 to do what?

A

to dorsalize mesoderm into notochord and paraxial mesoderm in caudal region of the embryo.

68
Q

What antagonizes BMP4?

A

Brachyury (T) gene

69
Q

What genes are important in head formation?

A

OTX2, LIM1 , HESX1, secreted factor cerebrus

70
Q

What will activating BMP4 with FGF result in?

A

Ventralizing ( lateral and intermediate)

71
Q

What will blocking BMP4 and FGF ( using goosecoid , noggin and follistatin together) result in?

A

Dorsalizing ( paraxial mesoderm and notochord.)

72
Q

Why was goosecoid used to dorsalize the embryo/ whats the purpose of dorsalizing the embryo?

A

So that the notochord is positioned in the back of the baby not the stomach

73
Q

_____secreted by the node and primitive streak, establishes ______,

A

FGF8
Nodal

74
Q

What secretes FGF8?

A

Node and primitive streak

75
Q

FGF8 secreted by the node and primitive streak, establishes Nodal and then nodal proteins …

A

accumulates on the left side of
the node.

76
Q

What is Nodal?

A

a member of TGF-β superfamily

77
Q

Why are they called “LEFTY-1” and “ LEFTY-2” ?

A

Because they can only be found on the left side

78
Q

As the neural plate starts to form, neurotransmitter serotonin (5HT)

A

increases in concentration on the left side

79
Q

As the neural plate starts to form, neurotransmitter serotonin (5HT) increases in concentration on the left side. Why?

A

because of its metabolism by MAO on the right.

80
Q

What happens under the influence of 5HT?

A

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
Q

What also participates in induction of Nodal, LEFTY-1, and LEFTY-2?

A

Products of Brachyury (T), expressed in the notochord

82
Q

Expression of Nodal and LEFTY-2 regulates…

A

expression of the transcription factor PITX 2, which, through further downstream effectors, establishes left-sidedness.

83
Q

What establishes left sidedness through further downstream effectors?

A

PITX2

84
Q

where is SHH expressed?

A

In the notochord

85
Q

SHH possibly serves as a

A

as a midline barrier and also represses expression of left-sided genes on the right.

86
Q

Expression of the transcription factor Snail may regulate

A

downstream genes important for establishing right-sidedness.

87
Q

What germ layer is the nervous system derived from?

A

Ectoderm

88
Q

What germ layer is the sensory epithelium of eye , ear, nose derived from?

A

Ectoderm

89
Q

What germ layer is the epidermis , haur, and nails derived from?

A

Ectoderm

90
Q

What germ layer is the mammary and cutaneous glands derived from?

A

Ectoderm

91
Q

What germ layer is the epithelium of sinuses oral and nasal cavities , intraoral glands derived from?

A

Ectoderm

92
Q

What germ layer is the tooth enamel derived from?

A

Ectoderm

93
Q

What germ layer are the muscles derived from?

A

Mesoderm

94
Q

What germ layer are the CT derivatives : bone cartilage, blood,dentin, pulp, cementum, periodontal ligament derived from?

A

Mesoderm

95
Q

In reference of the notochord whats the most lateral epiblast cell going to give rise to?

A

Extraembryonic mesoderm

96
Q

In reference of the notochord whats the most medial epiblast cell going to give rise to?

A

Paraxial mesoderm

97
Q

In reference to notochord list the fate map of the epiblast cells from most medially to most laterally.

A

Paraxial mesoderm
Intermediate mesoderm
Lateral plate mesoderm
Extraembryonic mesoderm

98
Q

What germ layer are the GI tract epithelium and associated glands derived from?

A

Endoderm

99
Q

Malformation of head region

A

Can be duplication, malformation, or conjoined twins

100
Q

Cause of malformation of head region

A

Over / under expression of goosecoid which activates BMP4 inhibtors

101
Q

Malformation of lumbosacral region 2 egs

A

Sirenomelia ( caudal disgenesis) and sacrococcygeal teratoma

102
Q

Range of defects of sirenomelia

A

Hypoplasia

Fusion of lower limbs

Vertebral abnormalities

Renal agenesis

Anomalies of genital organs and imperforate anus

103
Q

Cause of sirenomelia

A

Insufficient mesoderm formation in caudomost region of embryo/ loss of mesoderm in lumbosacral region

104
Q

What is associated with sirenomelia?

A

Maternal diabetes

105
Q

Sacrococcygeal teratoma

A

Tumors may become malignant and are most common in female fetuses

106
Q

Cause of sacrococcygeal teratoma

A

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
Q

Failure of establishment of normal L-R asymmetry ( situs inversus)

A

Failure to properly establish L-R axis

108
Q

Situs solitus

A

Normal positioning of internal organs

109
Q

What is important for establishing laterality?

A

Neurotransmitter serotonin (5HT)

110
Q

What do laterality defects cause?

A

Complete reversal of organs

Embryology (6 decks)

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