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Embryology: Summer Semester > Unit 1.L2-Gastrulation,Trilaminar Embryo and Organogenetic Period > Flashcards

Unit 1.L2-Gastrulation,Trilaminar Embryo and Organogenetic Period Flashcards

1
Q

3.5 week

What disappears and what developes surrounded by the trophoblast cells?

A

The primary umbilical vesicle disappears & the secondary umbilical vesicle develops surrounded by the trophoblast cells (calipers).

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2
Q

What are the symptoms of pregnancy?

A
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3
Q

What happens when bleeding is interpreted as menstruation?

A

an error occurs in determining the expected delivery date of the fetus

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4
Q

What is the origin of germ layers and extra embryonic tissues?

A
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5
Q

What defines embryonic Cranial-Caudal directionality?

A

Prechordal plate

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6
Q

What always forms at the end of week 2?

A

secondary umbilical vesicle (yolk sac) forms and enlarges

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7
Q

What is a key step in week 3

A

gastrulation

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8
Q
  • What is gastrulation?
  • What does it begin with?
A
  • Gastrulation is the conversion of the epiblast (bilaminar into a trilaminar embryonic disc consisting of endoderm, mesoderm, and ectoderm”.
  • begins with the formation of the primitive streak
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9
Q

When does morphogenesis begin?

A

end of D14

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10
Q

What is the result of gastrulation?

A

the three germ layers & PGCs

  • 3-germ layers instructs the formation of adult body plan & all body tissues
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11
Q

What is the process of initation of gastrulation entails? (caudally and cranially)

A
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12
Q

The primitive streak elongates how and from what?

A

The primitive streak elongates “medially (caudal->cranial) from the thickened dorsal epiblast surface of the bilaminar embryo

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13
Q

How does the bilaminar embryonic disc goes to trilaminar embryonic disc?

A
  • Primitive streak gives rise to the Mesoderm layer
  • The Epiblast is now called the “Ectoderm layer”
  • The Hypoblast is replaced by “Endoderm layer
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14
Q

Axial Orientation is Established:

A

Cranio-Caudal & Dorso-Ventral axis gives “bilateral symmetry” to the embryo.

  • Cranial Side: Prechordal plate
  • Caudal Side: Primitive streak
  • Dorsal Side: Ectoderm
  • Ventral side: Hypoblast->Definitive Endoderm
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15
Q
  • What does the caudal end of the primitive streak do?
  • What does the cranial end of primitive streak form?
A
  • Caudal end of Primitive streak elongates by cell proliferation
  • Cranial end of primitive streak has continuous cell proliferation that “pile-up” to form the primitive node

All cells are destined to go to the prechrondal plate but also in

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16
Q

How is the primitive groove formed?

A

by medial invagination of epiblast cells. It is a narrow linear depression within the primitive streak.

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17
Q

How is the primitive pit formed?

A

is formed by a depression (cranially) in the primitive node

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18
Q

What does the primitive streak cells do to become mesoblast?

A

Primitive streak cells “ingress” between the epiblast & hypoblast and become mesoblasts( between epi and hypoblasts)

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19
Q

What is ingression?

A

vital step for epiblast to change to squamos (spindly) so they can move inside

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20
Q

Definitive embryonic endoderm formation:

A

Cells from the epiblast, primitive node & primitive streak, displace the hypoblast, forming definitive embryonic endoderm cells in the roof of the umbilical vesicle

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21
Q

What does The remaining dorsal epiblast cells form?

A

Embryonic ectoderm

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22
Q

Where are the mesoblasts? what do they give rise to?

A

The Mesoblasts are sandwiched, forming the middle layer, which gives rise to: “Intraembryonic Mesoderm”

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23
Q

The three germ layers form what?

A

trilaminar embryo

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24
Q

What do cells move through?

A

primitive pit

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25
Q

What is displaced to extraembryonic regions, forming the wall of the umbilical vesicle?

A

hypoblast cells

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26
Q

Where does the mesoderm cells in the primitive node migrate to and form?

A

Move to top by going down in the pit under the epiblast
Cranially, the “mesoderm cells” in the primitive node migrate to form the notochordal process. (top arrows)

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27
Q

Primitive node cont to grow towards what?

A

prechordal plate

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28
Q

The cells from the Primitive pit continue to move where?

A

move ventrally towards the hypoblast

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29
Q

What does the primitive pit allow?

A
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30
Q

What is the mesoblast migration pattern?

A
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31
Q

What defines the future mouth?

A

Notochordal process at Prechordal plate defines future mouth; the Stomodeum.

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32
Q

What forms the future mouth?

A

Cranially, at the Stomodeum, ectoderm fuses to the endoderm, forming the oropharyngeal membrane, which dissolve to form the future mouth.

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33
Q

What forms the primodial anus or proctodeum?

A

Caudally, the ectoderm fuses to the endoderm, forming the cloacal membrane, which dissolves to form the primordial anus; the Proctodeum

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34
Q

The notochordal process grows so fast until it touches what? what happens

A

touch precordial plate, oropharyngeal membrane when noto touches

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35
Q

T/F: nonchordal process is endoderm origin?

A

False: mesoblast

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36
Q

What happens to the primitive steak to effect notochordal process?

A
  • Primitive streak shortens but adds cells to elongate the notochordal process
  • The notochordal process lengthens by cranial migration of mesodermal cells from the node under the epiblast
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37
Q

the (notochordal process + adjacent underlying mesoderm) =

A

induce the overlying “embryonic ectoderm FIELD” to form the neural plate->(future CNS).

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38
Q

What does morphigins and mesodermal cells on the side form?

A
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39
Q

Notochordal process grows how? Then what does it do?

A
  • The notochordal process grows cranially under the embryonic ectoderm at the primitive pit until it reaches the Prechordal plate.
  • Notochordal process splits ( and mouth)
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40
Q

Notochordal process “splits” under the ectoderm & forms what?

A
  1. Lumen (the notochordal canal)
  2. Roof-layer of NC
  3. Floor-layer of NC
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41
Q

The Roof-layer of NC touches what? to induce what?

A

The Roof-layer of NC touches embryonic ectoderm to induceàNeural Plate (future CNS).

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42
Q

How does Notochord Originates from the Notochordal process?

A
  1. Floor-layer of the Notochordal Canal (NC) fuses with the embryonic endoderm, forming two layered floor.
  2. Then, both layers degenerate (Floor-layer of NC +Endoderm), thus the Roof-layer of NC touches the umbilical vesicle
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43
Q

After the floor layer of NC and endoderm degrades, primitive pit forms what?

A

The Primitive pit forms the Neurenteric canal linking the amniotic and umbilical vesicle cavities.

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44
Q

How do you form grooved notochordal plate?

A

Roof-layer of the notochordal canal flattens

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45
Q

What closes that neurenteric canal?

A

Cranial cell proliferation in the notochordal plate causes infolding, creating a cylindrical Notochord across the embryo

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46
Q

The notochord is the main inducer, driving what?

A

organ induction.

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47
Q

General neurulation?

A
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48
Q

“Infolding” of the Notochordal plate forms what?

A

forms a tube; the Notochord

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49
Q

Notochord induces the top ectoderm to thicken & form what?

A

nerual plate

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50
Q

What does the neural plate (neuroectoderm) form

A

forms CNS, brain, spinal cord & retina

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51
Q

As the notochord elongates, the neural plate broadens how?

A

cranially (below)

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52
Q

Neural plate goes down to ?

A

primitive node

53
Q

The neural plate invaginates along its central axis to form what?

A

a neural groove flanked by neural folds

54
Q

The neural folds become prominent where? What does it initate?

A

The neural folds become prominent at the cranial end, initiating brain development

55
Q

The Neural folds begin to move together to form what?

A
  • Neural Groove, which fuse both ends of the neural folds by day 21
  • WHen the epiblast move to the sides as the neural groove forms, they will become aminoblast, no longer ecto or neuroecto cells
56
Q

Neural tube forms the primordium of the:

A

(1) Brain vesicles &
(2) Spinal cord

57
Q

Because of the utube (horseshoe cavity), it gives rise to what?

A

somatopleure (mesoderm+ectoderm) and splanchopleure (mesoderm+endoderm)

58
Q

What does the splanchopleure form?

A

gut tube
Base of splanchopleure cells, start forming cardiogeneis mesodermal cells

59
Q

What shows up at day 21?

A

3 somites formed from paraxial mesoderm

60
Q

What is utube?

A

Horse show shaped canal which is imp for formation of blood islands and cardiogen. mesoderm

61
Q

How does utube formed?

A

lacuae of intraembryonic coelom forms the utube

62
Q
  • Neural fold is flanked by what?
  • Neural folds fuse and the nerual crest cells migrate how?
  • Neural crest via?
A
  • Neural fold is flanked by neural crest cells
  • Neural folds fuse & the cells migrate ventro-laterally
  • Neural Crest via epithelial to mesenchymal transition (EMT) (move out away from neural tissue) migrate into the mesodermal layer-> more lateral dorsal and form ganglia on both sides
63
Q

How is the continuous epidermis later formed?

A

Surface ectoderm becomes delaminated and fuses to form

64
Q

Neural crest cells further migrate laterally, forming the

A

spinal ganglia

65
Q

The paraxial mesoderm (PM), emerges from what? What does it become?

A

The paraxial mesoderm (PM), emerges from the primitive node between the neuroectoderm and endoderm & laterally becomes intermediate mesoderm & lateral mesoderm

66
Q

Lateral mesoderm is continuous with what?

A

umbilical vesicle (bottom) and amnion (top)

67
Q

the paraxial mesoderm differentiates, condenses, & divides into what?

A

somites in a Cranio-caudal sequence

68
Q

What is somite period?

A
  • Day 20-30 (Somite Period): 38 pairs of somites, forming “axial skeleton” laid
  • All done from paraxial mesoderm

day 20: first somite stage

69
Q

What does lateral mesoderm make? Intermediate mesoderm?

A

Intermediate: gonads, kidneys
Lateral: cardiogram

70
Q

Intraembryonic Coelom space fuses to form what?
What does it split?

A

form horseshoe-shaped cavity, intraembryonic coelom by splitting the lateral mesoderm

71
Q

What does the lateral mesoderm split into?

A
72
Q

Early development of cardiovascular system?

A
73
Q

Vasculogensis and angiogensis?

A
74
Q

The heart & great vessels originate from what?

A

cardiogenic mesoderm (derived from lateral plate mesoderm) present at the cranial most region.

75
Q

Lacunae in the lateral mesoderm contribute to the formation of what?

A

pericardial coelom (which gives rise to the pericardium).

76
Q

Paired, endothelial-lined endocardial heart tubes fuse & form what?

A

form a primordial heart tube from the splanchnic mesoderm adjacent to the endoderm and the chorionic sac (yolk sac)

77
Q

2nd chorionic villus and tertiary?

A
78
Q

How do you form a a functional cardiovascular system having
3 branches by day 26

A

The heart tube joins with blood vessels in the embryo, connecting the stalk, chorion, and umbilical vesicle

79
Q

What are the 3 branches of functional cardiovascular system?

A

look at page 38

80
Q

What does week 4 begin?

A

organogenetic - 4-8 weeks all the organs are formed

81
Q

What s the most critical and senstive period?

A

4th week

82
Q

Human development in utero occurs in three phases that are interrelated:

A
83
Q

What does the folding of embryo require?

A
84
Q

Besides the folding of embryo, what are other important events during organogenetic phase?

A
  • development of main organs: primordia of all tissues and organs formed
  • Constriction at the embryo-umbilical vesicle junction-> 2nd yolk sac undergoes constriction
85
Q

Folding of the flat trilaminar embryonic disc converts the embryo into what?

A

cylinder, defining major external & internal embryonic structures.

86
Q

Til lDay21embryo is straight with4-12 somites and begins to fold by day _

A

22

87
Q

Cranially,the neural folds form what?

A

brain primordium projecting dorsally & later folding ventrally by end of D22

88
Q

the neural crest cells starts moving where

A

intra-embryonic mesoderm and the primordium of the brain is formed dorso-cranially, but is bent/folded ventrally

89
Q

Ventral inversion:

A

Primordial heart, Pericardial coelom + septum transversum

90
Q

As the heart moves, endodermal region forms what?

A

septum transverum-> will move with heart and give rise to diagram

91
Q

The septum transversum ,primordial heart, pericardial coelom, and oropharyngeal membrane begins to do what?

A

Positional inversion and fold vertally

92
Q

Till Day21 septum transversum lies how?

A

cranially to the heart, & is not inverted

93
Q

What does the septum transverum give rise to?

A

future diaphragm, thus partitioning the abdominal cavities and thoracic cavities. (separates out the lungs and heart from visera)

94
Q
  • How does the forebrain inverts?
  • What does the folding bring?
A
  • ventrally
  • Folding brings umbilical vesicle endoderm to form the foregury (primodium of pharynx, esophagus, and lower respiratory system) which lies between the forebrain and primordial heart
  • The Stomodeum emerges due to this folding.
95
Q

Why is the heart moving?

A

amnion is decending down and pinching

96
Q

rapid growth of the caudal neural tube forms what? What does it consist of?

A

rapid growth of the caudal neural tube forms the tail fold, consisting of spinal cord primordium.

97
Q

caudal eminence projects over what? What does this form?

A

caudal eminence projects over the cloacal membrane, forming the future anus.

98
Q

Between D22-26, the rapid growth of spinal cord, causes what?

A

inverts the allantois (a sac like structure), connects the fetal bladder to the yolk sac and removes nitrogenous wast via umbical sac vasculature

99
Q

What fuses together to make umbilical cord?

A

Connecting stalk and umbilical vesicle

100
Q

Cranially, the forebrain develops how?

A

beyond the stomodeum and overhangs the developing heart

101
Q

How is the omphaloenteric duct formed?

A

Constriction at the embryo-umbilical vesicle junction becomes prominent & a Omphaloenteric duct is formed

102
Q

Why do we have heart in right place

A

axial folding

103
Q

What is the Omphaloenteric duct

A
  • connection between midgut and umbilical vesicle
  • Will stay so when intesting grows, it has a space until the body grows more
104
Q

Later, a constriction in the Omphaloenteric duct defines the formation of what?

A

Umbilical cord

105
Q

What does the nerual crest cells form?

A

Neural Crest cells have now formed well defined spinal ganglia flanking the neural tube.

106
Q

What surround the midgut?

A

dorsal mesentery

107
Q

Horizontal folding (rolling across the width) of the embryo produces what?

A

right and left lateral folds

108
Q

ventrolateral abdominal wall fold towards what? What does this cause?

A

ventrolateral abdominal wall fold toward the median plane, converting the disc-shaped embryo->into a cylindrical embryo.

109
Q

spinal cord broadens and what grows?

A

somites grow laterally

110
Q

For the cylindrical human embryo, the Folding takes place in two directions, what are they?

A

Longitudinal (cephalo-caudal) folding is due to rapid enlargement of the cranial end of the neural tube & the form of the primordial brain

Lateral or transverse: Lateral folding is a consequence of the rapid enlargement of the somites. The process of lateral folding brings the amnioblast down to wrap around the embryo, pinching the yolk sac & forming the body wall

111
Q

What forms the body wall?

A

Somatopleure

112
Q

Lateral folding fuses 3 germ layers on the left & right to fuse & form what?

A

a cylinder

113
Q

the endoderm in the center forms what?

A

midgut; a primordium of the small intestine

the foregut & hindgut are already defined.

114
Q
  • Lateral folding squeezes what?
  • What is the result of this?
A

Lateral folding squeezes the yolk sac & reduces the connection between midgut & umbilical vesicle (yolk sac), forming an Omphaloenteric duct

115
Q

What does the ectoderm, mesoderm and endoderm give rise to?

A
116
Q

Major morphological changes in the embryo occurs during what week?

A

4th week

117
Q

What are the Morphological changes in the Early Fourth Week (Day 22-23)

A
  • Day22: (4th week) the embryo is straight with ~4-10 somites.
  • Day23: The medially placed neural tube has 8-10 somites, & neural tube is open to the amniotic cavity at the cranial and caudal ends through the rostral and caudal neuropores.
118
Q

Do we need the rostral and caudal neuropore open or closed

A

need to close it or the amnionic fluid will come in -> damage spinal cord and cause spinal bifida

119
Q

When does the 1st pharyngeal arch form and the pumping of the heart

A

day 24

120
Q

What does the first pharyngeal arches form?

A

pair of pharyngeal arches (mandibular arch) emerge, which will later form the mandible (lower jaw) & maxilla (upper jaw).

121
Q

What does the embryo continue to do?

A

continues to fold, showing ~13 somites

122
Q

What happens to the heart on day 24?

A

The heart starts pumping blood (rhymmical) ; seen at the heart prominence

123
Q

rostral neuropore or caudal neruopore close first?

A

rostral neuropore closes; caudal neuropore remains open for longer period of time.

124
Q

Upper limb buds develop as what?

A

small swellings on the ventrolateral body.

125
Q

As the Lower limb buds emerges, what closes and emerges?

A

caudal neuropore closes
& nasal placode prominently emerges.

126
Q

Primordial organ systems form:

A

large primordial heart defines atrium & ventricular prominences

127
Q

Why are the limbs lower in the embryo?

A

becasue the head is growing more

128
Q

In late fourth week, what happens?

A
  1. Three pairs of pharyngeal arches emerge at 27-somite stage.
  2. Rostral neuropore closes, the fore brain enlarges and embryo is C-shaped.
  3. The lens placode (for the eye) and the otic pit (future internal ear) & the nasal placode develop
129
Q
  • The neural fold fuses to form what?
  • What does neural tube does?
A

Neural fold fuses to form the neural tube
the neural tube delaminates from the ectoderm

Embryology: Summer Semester (10 decks)

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