Embryology - Formation of embryonic germ layers

Question 1

What is the gastrulation

Answer 1

Bilaminar disc is converted into trilaminar disc (3 germ layers)

Question 2

What is called the 3 germ layers?

Answer 2

Gastrula

Question 3

What is the morphogenesis

Answer 3

the development of the body, the most vulnerable period

Question 4

What is the notochord?

Answer 4

Axial orientation is established around which the axial skeletal forms

Question 5

What marks the 3rd week period?

Answer 5

The beginning of the Embryonic period

Question 6

What are Somites

Answer 6

(soma: body) responsible of the segmental development of embryonic body walls

Question 7

What is the neurulation?

Answer 7

Neural plate appears and folds into neural tube

Question 8

What is the neural tube

Answer 8

The primordium of the central nervous system

Question 9

What is the intraembryonic coelom ?

Answer 9

Initiate the formation of body cavities

Question 10

What is the implantation bleeding and when does it happen?

Answer 10

3rd week coincides with 1st missed menstrual period (5weeks after first day of the last normal menstrual period): Error in determining delivery date (before ultrasound datation)

Question 11

During gastrulation:

• what is the first sign of gastrulation and what does it create?

Answer 11

Migration of epiblastic cells towards the midline (caudal to cranially), creates the primitive streak

Question 12

During gastrulation:

What defines the primitive streak?

Answer 12

defines the bilateral symmetry (cranial/caudal, ventral/dorsal, and the rght/left)

Question 13

During gastrulation:

what is the primitive node

Answer 13

cells who proliferate at the cranial end to form the primitive node

Question 13

During gastrulation:

What is the primitive pit?

Answer 13

Invagination of epiblastic cells from primitive streak & node creates the primitive pit

Question 14

During gastrulation:

What is primitive groove

Answer 14

when the primitive pit leaves a groove as it progresses cranially

Question 15

How do you call the migrating epiblastic cells and what does it give rise to?

Answer 15

Mesenchymal cells

Question 16

During gastrulation:

What happens when the epiblastic cells migrate medial to latero-cephalic between epiblast and hypoblast layers?

Answer 16

It forms a 3rd layer called intraembryonic mesoderm

Question 17

During gastrulation:

what is created when migrating epiblastic cells displace and replace hypoblast cells?

Answer 17

Embryonic endoderm

Question 18

There are 2 zones where ectoderm and endoderm remain fused (no mesoderm), what are they

Answer 18

1. Prechordal plate
2. Cloacal membrane

Question 19

During gastrulation:

What will arise from prechordal plate

Answer 19

It will give rise to oropharyngeal membrane (future site of oral cavity)

Question 20

During gastrulation:

What will arise from cloacal membrane

Answer 20

future site urogenital meatus and anus

Question 21

High yield slide that describes gastrulation in brief (to review only)

Answer 21

Question 22

What happens when the intraembryonic mesoderm reaches the margin of the emryonic disc?

Answer 22

it fuses with the extraembryonic mesoderm

Question 23

So, in review. What are the 3 layers of the trilaminar embryoninc disc and from which cells they all come?

Answer 23

• embryonic ectoderm
• intraembryoninc mesoderm
• embryoninc endoderm

All coming from the epiblast

Question 24

What arises from embryonic ectoderm?

Answer 24

epidermis, central & peripheral nervous system, eyes & internal ears, neural crest cell & many connective tissue of the head

Question 25

What arises from intraembryoninc mesoderm

Answer 25

skeletal muscles & connective tissue, blood cells, lining of blood vessels, viscera’ smooth muscles

Question 26

What arises from embryonic endoderm

Answer 26

Gives rise to: epithelial linings of respiratory & digestive tracts, including associated glands

Question 27

What happens if primitive streak persist?

Answer 27

Cacrococcygeal teratoma - most common tumor in neonates - contains tissues derived from the 3 germ layers, varying stages of differentiation

Question 28

Explain the notochordal process and how it becomes the notochordal plate

Answer 28

hollowed cord formed medially by mesenchymal cells migrating from primitive node & pit, Elongate cranially between ectoderm & endoderm to prechordal plate (signaling center for cranial development) Will undergo changes to end as a flattened grooved plate: notochordal plate

Question 29

what happens at the cranial end of the embryo when the notochordal plate proliferates and infolds?

Answer 29

Creates the notochord

Question 30

What it the notochord?

Answer 30

- Provides signals for the development of axial musculoskeletal system. - Will induce overlying ectoderm to thicken & form the neural plate (CNS) - Defines the primordial longitudinal axis of embryo, and some rigidity

Question 31

What gives rise to somites?

Answer 31

Paraxial mesoderm

Question 32

what arises from intermediate mesoderm?

Answer 32

urogenital system

Question 33

what arises from lateral mesoderm + ectoderm?

Answer 33

Intraembryonic somatic mesoderm: anterior body wall - + endoderm: Intraembryonic splanchnic mesoderm: digestive tube wall

Question 34

Role of somites?

Answer 34

give rise to most of axial skeleton, muscles, dermis of associated metamerix segments

Question 35

What can determine the embryo's age around 4-5 wks?

Answer 35

The somites

Question 36

3 steps of the formation of the neural tube

Answer 36

1. notochord to neural plate 2. invagination of the neural plate around its central axis and creates neural groove with neural folds 3. neural folds begin to fuse and creates the neural tube

Question 37

First sign of brain development

Answer 37

neural folds becomes prominent at cranial end

Question 38

what arises from neural crest cells?

Answer 38

Spinal & autonomic nervous system ganglia Suprarenal medulla, other organs & tissue

Question 39

Is the neural tube seperated from the ectoderm?

Answer 39

Yes

Question 40

When is neurulation completed?

Answer 40

end of 4th week

Question 41

what can result from disturbance of the neurulation process6

Answer 41

brain deffect and spinal chord deffects (anencephaly, spina bifida)

Question 42

Intraembryoninc ceolom in brief

Answer 42

dividing the lateral mesoderm into 2 parts: 1. Intraembryonic somatic (parietal) mesoderm: with ectoderm form the body wall or somatopleure 2. Intraembryonic splanchnic (visceral) mesoderm: with endoderm form embryonic gut or splanchnopleure Will result in the formation of body cavities

Question 43

What is the most common teratogen

Answer 43

Alcohol, vulnerability between weeks 4-8

Question 44

What is the mos common cause of nonheritable intellectual disability

Answer 44

Fetal alcohol spectrum disorder (FASD)

Question 45

what is a teratogen

Answer 45

agent or factor causing abnormal embryonic and fetal development

Question 46

what are the specific pattern of minor facial features of FASD

Answer 46

small eyes, smooth philtrum, thin upper lip

Question 47

Central nervous system symptoms from FASD

Answer 47

Cognition, motor coordination, attention, language development, executive functions, memory, social perception and emotion processing are impaired to a variable extent