Why are the layers of the early embryo important?

They give rise to the cell types, goes from xygote to blastocyst and then gastrula Germ cells = sperm or egg endoderm (internal) layer = lung alveoli, thyroid, pancreatic cell Mesoderm (middle) layer = cardiac muscle, skeletal muscle, tubule cell of kidney, RBC, smooth muscle. Ectoderm (External layer) = epidermis skin cells, neuron, pigmant cell.