Germ Layers

Within a developing embryo, three germs layers give rise to the various structures of the body. First of which is the endoderm. This is the inner layer of skin within the embryo that gives rise to the lining of most digestive and respiratory tracks. The endoderm is responsible for the glandular material associated with the digestive and respiratory tracks as well. The layer behind the endoderm is the mesoderm. Mesodermal derivations include the appendicular muscles, various connective tissues, and blood vessels. Lastly, the outer germ layer of the embryo is the ectoderm. This layer is responsible for the formation of the epidermis, the nervous system and the neural crest cells. Neural crest cells are a unique cell formed by the remanence of the neural fold after it closes over and establishes the neural tube. The neural crest cells travel through the body and establish the foundation for the visceral skeleton, pigment and photoreceptive cells, sensory and postganglionic neurons, and the dentine producing cells of teeth. Without these germ layers, the remaining structures of the body would be compromised and we would essentially be blobs of flesh and muscle.