The ectoderm is one of the three embryonic germ layers, along with endoderm and mesoderm, that form during gastrulation in early embryonic development. It is the outermost layer of cells that gives rise to various structures and tissues in the body.

The ectoderm originates from the outer layer of the embryo’s trilaminar disc, known as the epiblast. During gastrulation, it differentiates to form the surface ectoderm by migrating to the outside of the developing embryo.

The ectoderm gives rise to numerous tissues and structures, including the epidermis (outermost layer of the skin), hair, nails, sweat glands, mammary glands, tooth enamel, lens and cornea of the eye, sensory neurons, sensory organs (such as the ear and nose), pituitary gland, adrenal medulla, and parts of the central nervous system (including the brain and spinal cord).

Throughout embryonic development, the ectoderm interacts with other germ layers to form complex structures and organs. It undergoes further specialization and segmentation to form the neural tube, which gives rise to the central nervous system, and the neural crest cells that contribute to various components of the peripheral nervous system, facial structures, and other cell types.