Embryonic Period Flashcards
What happens to the epiblast in the third week?
Formation of the primitive streak long dorsal surface of epiblast
What is found at the cranial end of the primitive streak?
Primitive node
What is found within the primitive node?
Primitive pit
What happens in the third week?
Gastrulation
What happens in gastrulation?
Two cells layers become three germ cell layers
How does gastrulation occur?
Epiblast cells divide and migrate towards the primitive pit
Cells push though epiblast to form 3 new layers
What are the 3 germ cell layers?
Endoderm
Mesoderm
Ectoderm
What forms the endoderm?
Epiblast cells that migrate through the primitive pit and displace the hypoblast cells
What forms the mesoderm?
Epiblast cells that migrate through the primitive cells and lie between epiblst layer and new endoderm
What forms the ectoderm?
Epiblast cells that remain in position
What structures are derived from the endoderm?
Epithelial lining of GI tract Epithelial lining of respiratory tract Lining of urinary and repro systems Liver Pancreas
What structures are derived from the mesoderm?
Notocord
MSK system
Muscular layer of GI tract
Circulatory system
What structures are derived from the ectoderm?
Epidermis of skin
Cornea + lens
Nervous system
What is neuralation?
Formation of the neural tube?
What initiates neuralation?
Week 3 - notochord appears in the mesoderm
What is the effect of the notochord?
Secretes growth factors which stimulate differentiation of overlying ectoderm into neuroectoderm - forms neural plate
How does the neural plate form the neural tube?
Lateral edges of plate rise to form neural folds -> fuse in midlne to form neural tube
What is the neural crest?
During folding some cells migrate to form the neural crest
What are somites?
Organistion of paraxial mesoderm into segments
How many somites do we end up with?
31
What is derived from somites?
Dermatome - skin section
Myotome - muscle section
Sclerotome - hard tissue section
What is the relevance of the segmentation into somites?
Gives rise to repeating structures
- vertebrae
- spinal cord segements
- spinal nerves
What happens in the 4th week?
Folding of the embryo
What ways does the embryo fold?
Cephalocaudal
Lateral
What does folding achieve?
Draws together margins of the disk
- creates ventral body wall
- pulls amniotic membrate around disk
- pulls connecting stalk ventrally
Forms new cavity within embryo
