Ektoderm

Ektoderm, also spelled ectoderm, is the outermost of the three primary germ layers in animal embryos. It forms during gastrulation and, with the endoderm and mesoderm, establishes the foundational tissues that shape an organism’s external appearance and nervous system.

During development, the ectoderm differentiates into surface ectoderm and neuroectoderm. The neuroectoderm gives rise to the neural plate, which folds to form the neural tube, the precursor to the central nervous system. Neural crest cells arise at the border of the neural plate and contribute to a wide range of tissues, including peripheral nerves, glia, melanocytes, and craniofacial cartilage and bones.

Derivatives of the surface ectoderm include the epidermis and its appendages (hair, nails, and glands of the skin), as well as ocular structures such as the lens and cornea, and the mucosa of the oral and nasal cavities. The oral ectoderm also contributes to the enamel of teeth. The adenohypophysis (anterior pituitary) develops from Rathke’s pouch, an invagination of surface ectoderm, while the neuroectoderm forms the brain and spinal cord.

Clinical relevance includes ectodermal dysplasias, a group of disorders affecting skin, hair, nails, and teeth, as well as neural tube defects linked to disrupted ectodermal development. Understanding ectodermal derivatives clarifies the coordinated formation of skin and nervous system structures during early embryogenesis.