crucial structure in transformation of bilaminar into trilaminar embryo
When does implantation begin?
What happens in the 2nd week when implantation continues?
Embryo is at bilaminar blastoderm stage
By bilaminar blastoderm development the period of blastogenesis terminates and begins the period of embryogenesis
When is implantation completed
What happens in the thrid week after implantation?
development of bilaminar into trilaminar blastoderm/embryo
consisting of 3 germ layers: ectoderm, mesoderm, endoderm
Primitive streak functions
morphogenetic centre in mesoderm, endoderm and ectoderm development
regulate epiblast cells migration and differentiation, that invaginate in its axis
production of particular growth factor s/morphogens
FGF8- fibroblast growth faktor
E-cadherin expression decrease in epiblast cells
3 germ layers develop from EPIBLAST: which and how are they arranged?
ectoderm and endoderm are arranged as epithelium = CAM +
mesoderm is not arranget as epithelium, histologically it is connective tissue – primary mesenchyme = CAM -
Development of notochord / chorda dorsalis
epiblast precursor, invaginating in Hensen's primitive node, migrate toward the prechordal plate, creating the cord-like cellular axial structure, s.c. notochord
Cranio-caudal axis I
Cell signaliling from the area of rostral/cranial end of embryo, anterior visceral mesoderm, AVM genes OTX2, LIM1, HESX1 and factor Cerebrus - determine the head end (before the primitive straek formation)
Cranio-caudal axis II
Cell - signalling from primitive node and notochord, gen Brachyury – dorsal mesoderm formation in the middle and caudal part of embryo
FGF8 – fibroblast growth factor – determine, what will differentiate in ventral mesoderm – kidneys, gonads, bloodm vessels
Dorso-ventral axis - mesoderm dorsalisation
Noggin, Chordin, Follistatin block the BMP , that results in notochord and somites formation, neuroectoderm diffrenetiation from ectoderm, differentiation of notochord and paraxial mesoderm
Neural plate induction mechansim?
interaction of notochord with adjacent ectoderm
Noggin, Chordin, Follistatin, neural inductors, for ectoderm to neuroectoderm in the region of forebrain and midbrain
Hindbrain and spinal cord are induced by WNT and FGF expressed in the region of the caudal morphogenetic system.
Secondary neurulation/ neural tube development in hindbrain and spinal cord region
caudal morphogenetic centre – intensive proliferating caudal end of notochord •caudal end of notochord gets beneath the primitive streak/primitive groove, that becomes determined to neuroepithelium at that region •primitive streak shortening •neural plate lengthening •neurulutaion (plate to tube development
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