1.3: Week 3- Trilaminar Germ Disc ✅ Flashcards
After implantation, what is the bilaminar embryo made up of?
2 layers sandwiched between 2 cavities
Epiblast and Hypoblast between amniotic cavity and blastocyst cavity
What is the most characteristic event during week 3?
Gastrulation-> trilaminar embryo
Establishes 3 germ layers in the embryo
-ectoderm
-mesoderm
-endoderm
Begins with formation of primitive streak of the surface of the epiblast
Germ layer
Group of cells in an embryo
The layers interact with each other as embryo develops
-eventually give rise to all organism’s tissues and organs
Ectoderm
Outer body tissues
-skin, nails, teeth
-nerves, eyes, lining of mouth
Mesoderm
Middle tissues
-blood and lymph, bone and notochord, muscle
-excretory and reproductive systems
Endoderm
Inner lining
-digestive system
-lining of respiratory, excretory and reproductive systems
What stage is highly sensitive for teratogenic insult?
Initiation of gastrulation
(Teratogens are things that cause abnormalities if fœtus is exposed)
When is organogenesis?
Weeks 3-8 aka Embryonic period
What axes does the human body have?
3
Rostrocaudal (AP)- front of brain to back
Dorsoventral- back to front
Left-right
When do axes need to be established?
Before organ formation
Axis establishment begins in the primitive node
Notochord: what, when formed, where?
Signaling center, for induction of axial skeleton and neural plate (neurulation)
Formed during gastrulation by mesoderm
Extends through length of future vertebral colum and up to anterior end of midbrain
-splits embryo into 2 equivalent sides
What does the notochord signal?
The ectoderm
To form the thick and flat neural plate (neuroectoderm)
Neurulation
Folding of neural plate into neural tube-> which later differentiates into CNS (spinal cord and brain)
Forms primitive CNS
Neurula
NTDs
Neural tube defects-> defects of brain or spinal cord
-when it fails to close in specific regions
Most common are spinabifida and anencephaly
Factors that cause NTD
-genetic
-nutritional (insufficient folate-B9)
-environmental
-multi factorial)
Types of NTDs
Anterior
-Anencephaly
-Iniencephaly
Middle
-Craniorachischisis
-Encephalocele
Posterior
-Open spinal bifida
-Closed spina bifida