Mesoderm II Heart: Migration of Splanchnic
Mesenchyme Endocardium Lateral Mesoderm Fuses and
Encircles Endocardium Heart Formation
• Amphibians
–
–
–
–
–
forms in pharyngeal region
splanchnic mesenchyme migrates
aggregates to form central tube: endocardium
fusion of lateral mesoderm (in ventral region)
encirclement of endocardium (towards dorsal
where layer fuses) Heart Formation
• Formation of three layers
– endocardium
– myocardium
– pericardium
• Myocardium then adheres to endocardium
to create the heart separated from
pericardium by pericardial cavity (coelom) Heart Formation
• So splanchnic mesoderm forms
endocardium and myocardium
• Somatic mesoderm forms pericardium
• In higher vertebrates. two endocardial tubes
form on each side and then fuse laterally Fusion of Endocardial Tubes Formation of Chick Heart Heart Formation
2 ventral aortae
• Heart tube develops two
bifurcations
• Then twists and divides
into chambers
2 vitelline veins Initial Heart Chambers Blood Vessels
• A complicated and plastic system
• Forms from
– aggregation of mesechymal angioblasts into
blood islands
• peripheral region makes endothelial lining
• central makes blood cells
– or aggregation of angioblasts without blood cell
formation
• Vessels surrounded by basement lamina and
smooth muscle Embryonic Blood Formation
Mesoderm II Part 1
of 12
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