Embryonic period
3 week – 8 week
origin of organs – organogenesis
by combination of cells originated from
3 germ layers
Beginning of embryonic period
embryo, stage 10, 23ED
according Carnegie classification
3,0mm
The end of embryonic period
Embryo, stage 23 , 56ED
according Carnegie classification
30,0 mm
Embryonic period
•
•
•
•
growth
segmentation
folding
organogenesis
(ectoderm, mesoderm)
(ectoderm, mesoderm)
(endoderm)
Growth
•
proliferation + extracellular matrix synthesis + cavities
formation
•
caudal morphogenetic system (cms) – principal growth
centre, embryo extension
•
head region – early growth - expansion, later growth during
fetal period
•
differentiation in head is an advance in early embryo
Segmentation
neuroectoderm a mesoderm
neuromeres - neuroectoderm, CNS – brain vesicles
somitomeres - somites - paraxial mesoderm
homeotic genes, HOX – rhombencefalon,
rhombomeres
OTX1, OTX2, EMX1, EMX2 – mesencephalon,
prosencephalon
Neural tube development in brain region
(segmentation in neuroectoderm - neuromeresbrain vesicles)
3 primary brain vesicles
wall
5 secondary brain vesicles
adult derivates
wall
cavity
forebrain
midbrain
hindbrain
cavities
Segmentation in paraxial mesoderm
Somitomeres
•
somitomeres in head region differentiate in muscles and
connective tissue of neurocranium / connective tissue in
splanchnocranium originates from neural crest!
•
somitomeres are differentiate into somites (starting in
cervical/neck region) by the activity of caudal
morphogenetic system
Somite differentiation
sclerotome, dermatome, myotome
epiteloid arrangement of somite
sclerotome –
connectives coating
spinal cord
dorsolateral cells
migrate to the limb
bud - muscles
Dorsomedial cells –
myotome –trunk
muscles
dorsally dermatom –
beneath ectoderm –
dermis in the skin
Molecular mechanism of somite differentiation
Differentiation of intraembryonic mesoderm
scanning electrom microscopy – tranversal section
Notochord, somites, intermediate mesoderm, lateral
mesoderm
Differentiation of intraembryonic mesoderm
transversal
section
Differentiation of intraembryonic mesoderm
transversal
section
Folding of the embryo
•
growth (cms, head region, somitogenesis)
•
2 folds tranversal – cranial and caudal (puncta fixata –
oropharyngeal membrane, cloacal membrane)
•
2 folds longitudinal, laterally, in longitudinal axis of embryo
Longitudinal and lateral folding
cervical and caudal
folds – 2 tranversal
folds
lateral foldings
contribute to
yolk/umbilical sac
invagination to the
body of the embryo
Organogenesis
Chick embryo