Embryology - Formation of embryonic germ layers Flashcards
What is the gastrulation
Bilaminar disc is converted into trilaminar disc (3 germ layers)
What is called the 3 germ layers?
Gastrula
What is the morphogenesis
the development of the body, the most vulnerable period
What is the notochord?
Axial orientation is established around which the axial skeletal forms
What marks the 3rd week period?
The beginning of the Embryonic period
What are Somites
(soma: body) responsible of the segmental development of embryonic body walls
What is the neurulation?
Neural plate appears and folds into neural tube
What is the neural tube
The primordium of the central nervous system
What is the intraembryonic coelom ?
Initiate the formation of body cavities
What is the implantation bleeding and when does it happen?
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)
During gastrulation:
- what is the first sign of gastrulation and what does it create?
Migration of epiblastic cells towards the midline (caudal to cranially), creates the primitive streak
During gastrulation:
What defines the primitive streak?
defines the bilateral symmetry (cranial/caudal, ventral/dorsal, and the rght/left)
During gastrulation:
what is the primitive node
cells who proliferate at the cranial end to form the primitive node
During gastrulation:
What is the primitive pit?
Invagination of epiblastic cells from primitive streak & node creates the primitive pit
During gastrulation:
What is primitive groove
when the primitive pit leaves a groove as it progresses cranially
How do you call the migrating epiblastic cells and what does it give rise to?
Mesenchymal cells
During gastrulation:
What happens when the epiblastic cells migrate medial to latero-cephalic between epiblast and hypoblast layers?
It forms a 3rd layer called intraembryonic mesoderm
During gastrulation:
what is created when migrating epiblastic cells displace and replace hypoblast cells?
Embryonic endoderm
There are 2 zones where ectoderm and endoderm remain fused (no mesoderm), what are they
- Prechordal plate
- Cloacal membrane
During gastrulation:
What will arise from prechordal plate
It will give rise to oropharyngeal membrane (future site of oral cavity)
During gastrulation:
What will arise from cloacal membrane
future site urogenital meatus and anus
High yield slide that describes gastrulation in brief (to review only)
What happens when the intraembryonic mesoderm reaches the margin of the emryonic disc?
it fuses with the extraembryonic mesoderm
So, in review. What are the 3 layers of the trilaminar embryoninc disc and from which cells they all come?
- embryonic ectoderm
- intraembryoninc mesoderm
- embryoninc endoderm
All coming from the epiblast
What arises from embryonic ectoderm?
epidermis, central & peripheral nervous system, eyes & internal ears, neural crest cell & many connective tissue of the head
What arises from intraembryoninc mesoderm
skeletal muscles & connective tissue, blood cells, lining of blood vessels, viscera’ smooth muscles
What arises from embryonic endoderm
Gives rise to: epithelial linings of respiratory & digestive tracts, including associated glands
What happens if primitive streak persist?
Cacrococcygeal teratoma - most common tumor in neonates - contains tissues derived from the 3 germ layers, varying stages of differentiation
Explain the notochordal process and how it becomes the notochordal plate
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
what happens at the cranial end of the embryo when the notochordal plate proliferates and infolds?
Creates the notochord
What it the notochord?
- 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
What gives rise to somites?
Paraxial mesoderm
what arises from intermediate mesoderm?
urogenital system
what arises from lateral mesoderm + ectoderm?
Intraembryonic somatic mesoderm: anterior body wall
- + endoderm: Intraembryonic splanchnic mesoderm: digestive tube wall
Role of somites?
give rise to most of axial skeleton, muscles, dermis of associated metamerix segments
What can determine the embryo’s age around 4-5 wks?
The somites
3 steps of the formation of the neural tube
- notochord to neural plate
- invagination of the neural plate around its central axis and creates neural groove with neural folds
- neural folds begin to fuse and creates the neural tube
First sign of brain development
neural folds becomes prominent at cranial end
what arises from neural crest cells?
Spinal & autonomic nervous system ganglia
Suprarenal medulla, other organs & tissue
Is the neural tube seperated from the ectoderm?
Yes
When is neurulation completed?
end of 4th week
what can result from disturbance of the neurulation process6
brain deffect and spinal chord deffects (anencephaly, spina bifida)
Intraembryoninc ceolom in brief
dividing the lateral mesoderm into 2 parts:
- Intraembryonic somatic (parietal) mesoderm: with ectoderm form the body wall or somatopleure
- Intraembryonic splanchnic (visceral) mesoderm: with endoderm form embryonic gut or splanchnopleure
Will result in the formation of body cavities
What is the most common teratogen
Alcohol, vulnerability between weeks 4-8
What is the mos common cause of nonheritable intellectual disability
Fetal alcohol spectrum disorder (FASD)
what is a teratogen
agent or factor causing abnormal embryonic and fetal development
what are the specific pattern of minor facial features of FASD
small eyes, smooth philtrum, thin upper lip
Central nervous system symptoms from FASD
Cognition, motor coordination, attention, language development, executive functions, memory, social perception and emotion processing are impaired to a variable extent
