Ectoderm

One of the three primary germ cell layers (the other two being the mesoderm and endoderm) that make up the very early embryo. The ectoderm is the outermost of the three layers. It differentiates to give rise to many important tissues and structures including the outer layer of the skin and its appendages (the sweat glands, hair, and nails), the teeth, the lens of the eye, parts of the inner ear, the nerves, brain, and spinal cord. This much is classic human embryology. Stem cell research, however, has shown that some cells within ectodermal structures retain their ability to differentiate into other tissues. For example, some cells in brain (ectoderm) can become bone marrow (mesoderm).

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The outer layer of cells in the embryo, after establishment of the three primary germ layers (e., mesoderm, endoderm), the germ layer in contact with the amnionic cavity. SYN: ectoblast (1). [ecto- + G. derma, skin]

- amnionic e. inner layer of the amnion continuous with body e..

- chorionic e. SYN: trophoblast.

- epithelial e. that part of the e. separating from the neuroectoderm at about the fourth week of embryonic life; the epidermis and its specialized derivatives develop from it. SYN: superficial e..

- extraembryonic e. derivative of epiblast outside the embryo's body.

- superficial e. SYN: epithelial e..

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ec·to·derm 'ek-tə-.dərm n

1) the outermost of the three primary germ layers of an embryo

2) a tissue (as neural tissue) derived from ectoderm

ec·to·der·mal .ek-tə-'dər-məl adj

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n.

the outer of the three germ layer of the early embryo. It gives rise to the nervous system and sense organs, the teeth and lining of the mouth, and to the epidermis and its associated structures (hair, nails, etc.).

• ectodermal adj.

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ec·to·derm (ekґto-dərm) [ecto- + derm] the outermost layer of cells of the three primary germ layers of the embryo. From it are developed the epidermis and the epidermal tissues, such as the nails, hair, enamel of teeth, and glands of the skin, the nervous system, the external sense organs such as the ear and eye, and the mucous membrane of the mouth and anus. Cf. endoderm and mesoderm. ectodermal, ectodermic adj