germ layer theory

The germ layer theory explains how the tissues and organs of the body develop from three primary layers that form early in embryonic development. These layers are called ectoderm, mesoderm, and endoderm. The ectoderm forms the skin, nervous system, and related structures. The mesoderm produces muscles, bones, blood vessels, and internal organs like the kidneys. The endoderm gives rise to the lining of the digestive and respiratory systems. These layers serve as the foundational blueprint for the body's complex structure, guiding the formation of all tissues and organs as the embryo grows.