Flashcards in Early Embryonic 2 Deck (17)
Define the bilaminar disc
Epiblast and hypoblast derived from embryoblast
Later forms trilaminar disc with formation of primitive streak
Define the germ layer
A layer from which other developed tissues originate from
What is the ectoderm?
Outermost layer of cells, giving rise to the epidermis and nerve tissue
What is the endoderm?
Innermost layer of cells giving rise to the gut lining
What is the mesoderm?
Middle germ layer, gives rise to muscle and bone
What is the primitive streak?
Narrow groove that develops on the dorsal(outer) surface of the epiblast
Orientates the embryo
What is gastrulation?
Reorganaisation of germ layers into the ectoderm, mesoderm and endoderm establishing the origin of all tissues
What is the trilaminar disc?
3 germ layers
Ectoderm, mesoderm and endoderm
List derivatives of the ectoderm
Brain and spinal chord
Retina and iris of eye
List mesodermal derivatives
Smooth,skeletal and cardiac muscle
Blood and blood vessels
What are the endodermal derivatives?
Lining of digestive tract
Gut derivatives e.g. Lungs
Describe migration and invagination during week 3
Cells on the epiblast migrate towards the primitive streak
They invaginate the epiblast and displace the hypoblast creating trilaminar disc
As more cells migrate through the streak they spread laterally and cephalod mesoderm spreads out between the ecto and endoderm leaving two gaps
Why does the mesoderm leave two gaps?
Vascularised so areas with gaps will becom necrotic and disintegrate leaving future mouth and anus
What is the notochord?
The notochord defines the phylum chordata, basis for the axial skeleton, drives formation of the nervous system
How is the notochord formed?
Prenotochordal cells of epiblast migrate through cranial part of primitive pit forming a solid rod of cells running in the midline eith an important signalling role
What happens to the notochord?
The vestigial remenant in adults is the nucleus pulposus of intervertebral discs which acts as a shock absorber