The three layers of embryology are the ectoderm, mesoderm, and endoderm. These layers form during gastrulation, which is a key stage of embryonic development. The ectoderm gives rise to structures such as the skin, hair, nails, and nervous system. The mesoderm gives rise to structures such as muscles, bones, cartilage, blood vessels, and the urogenital system. The endoderm gives rise to structures such as the lining of the respiratory tract, gastrointestinal tract, and associated organs such as the liver and pancreas. The three germ layers are essential for the development of a wide range of tissues and organs in the body.