Ektodermi

Ektodermi, or the ectoderm, is the outermost of the three primary germ layers formed during embryonic development. It arises during gastrulation from the epiblast and, as development proceeds, differentiates into two major components: the neuroectoderm and the surface ectoderm.

Neuroectoderm forms the nervous system through neurulation, giving rise to the brain and spinal cord. At the border with the surface ectoderm, neural crest cells emerge and migrate to contribute widely to the peripheral nervous system, melanocytes, craniofacial cartilage and bones, and several dental tissues. This lineage links ectodermal development to many structures of the head and face.

Surface ectoderm gives rise to the epidermis and its appendages, including hair, nails, and many glands such as sweat and mammary glands. It also contributes to sensory structures associated with the eye, notably the lens and cornea, and to the enamel organ that produces tooth enamel. In mature tissues, derivatives of the ectoderm support protective barriers, sensory perception, and interactions with the external environment.

Neural crest derivatives highlight the ectoderm’s broad role in forming both external coverings and diverse neural and craniofacial structures. Disruptions of ectodermal development can lead to ectodermal dysplasias, a group of conditions that affect multiple ectodermal derivatives. The prototypical example is hypohidrotic (anhidrotic) ectodermal dysplasia, characterized by sparse hair, altered dentition, and reduced sweat gland function.