ectoderm

Examples of ectoderm in the following topics:

• Development of the Integumentary System

  • The integumentary system develops from all embryonic layers (ectoderm, mesoderm and neural crest cells).
  • Fetal skin forms from three layers: ectoderm, mesoderm, and neural crest cells.
  • At four weeks gestation, simple ectoderm epithelium forms.
  • Ectoderm thickens into finger and toe nails.
  • Other regions of the ectoderm form into epithelial columns called cords which will become hair follocles and sebaceous and sweat glands.

• Gastrulation

  • During gastrulation, the embryo develops three germ layers (endoderm, mesoderm, and ectoderm), which differentiate into distinct tissues.
  • These three germ layers are known as the ectoderm, mesoderm, and endoderm.
  • In amniotes such as humans, gastrulation occurs in the following sequence: (1) the embryo becomes asymmetric, (2) the primitive streak forms, and (3) cells from the epiblast at the primitive streak undergo an epithelial to mesenchymal transition and ingress at the primitive streak to form the germ layers.The ectoderm gives rise to epidermis, and also to the neural crest and other tissues that will later form the nervous system.
  • The mesoderm is found between the ectoderm and the endoderm, giving rise to somites.
  • However, some common features of gastrulation across triploblastic organisms include: (1) A change in the topological structure of the embryo, from a simply connected surface (sphere-like), to a non-simply connected surface (torus-like); (2) the differentiation of cells into one of three types (endodermal, mesodermal, or ectodermal); and (3) the digestive function of a large number of endodermal cells.

• Neurulation

  • Following gastrulation, the neurulation process develops the neural tube in the ectoderm, above the notochord of the mesoderm.
  • Neurulation is the formation of the neural tube from the ectoderm of the embryo.
  • During gastrulation cells migrate to the interior of the embryo, forming the three germ layers the endoderm (the deepest layer), mesoderm (the middle layer), and ectoderm (the surface layer) from which all tissues and organs will arise.
  • In a simplified way, it can be said that the ectoderm gives rise to skin and nervous system, the endoderm to the intestinal organs, and the mesoderm to the rest of the organs.
  • During the third week of gestation, the notochord sends signals to the overlying ectoderm, inducing it to become neuroectoderm.

• Amnion Development

  • This cavity is roofed in by a single stratum of flattened, ectodermal cells called the amniotic ectoderm.
  • Its floor consists of the prismatic ectoderm of the embryonic disk.
  • Outside the amniotic ectoderm is a thin layer of mesoderm (continuous with that of the somatopleure), which is connected by the body-stalk with the mesodermal lining of the chorion.

• Tissue Development

  • During embryogenesis, the three germ layers (endoderm, mesoderm, and ectoderm) are formed from which all body tissues will later develop.
  • The top layer is now called the ectoderm.
  • The ectoderm is the start of a tissue that covers the body surfaces.
  • This image illustrates the types of cells produced by the ectoderm (external germ layer) of the developing embryo.
  • Compare the three embryonic germ layers (endoderm, mesoderm, and ectoderm) from which all body tissues develop

• Organogenesis

  • For example, some cells in the ectoderm will express the genes specific to skin cells.
  • The ectoderm forms epithelial cells and tissues, as well as neuronal tissues.
  • During the formation of the neural system, special signaling molecules called growth factors signal some cells at the edge of the ectoderm to become epidermis cells.
  • If the signaling by growth factors were disrupted, then the entire ectoderm would differentiate into neural tissue.
  • The central region of the ectoderm forms the neural tube, which gives rise to the brain and the spinal cord.

• Gene Expression for Spatial Positioning

  • For example, some cells in the ectoderm (the outer tissue layer of the embryo) will express the genes specific to skin cells.
  • The ectoderm forms epithelial cells and tissues, as well as neuronal tissues.
  • During the formation of the neural system, special signaling molecules called growth factors signal some cells at the edge of the ectoderm to become epidermis cells.
  • If the signaling by growth factors were disrupted, then the entire ectoderm would differentiate into neural tissue.
  • The central region of the ectoderm forms the neural tube, which gives rise to the brain and the spinal cord.

• Animal Characterization Based on Features of Embryological Development

  • Radially-symmetrical animals are diploblasts, developing two germ layers: an inner layer (endoderm) and an outer layer (ectoderm).
  • Diploblasts have a non-living layer between the endoderm and ectoderm.
  • The ectoderm develops into the outer epithelial covering of the body surface and the central nervous system.
  • During embryogenesis, diploblasts develop two embryonic germ layers: an ectoderm and an endoderm.
  • Triploblasts develop a third layer, the mesoderm, between the endoderm and ectoderm

• Cleavage, the Blastula Stage, and Gastrulation

  • The three germs layers are the endoderm, the ectoderm, and the mesoderm.
  • The ectoderm gives rise to the nervous system and the epidermis; the mesoderm gives rise to the muscle cells and connective tissue in the body; and the endoderm gives rise to columnar cells found in the digestive system and many internal organs.
  • The three germ layers give rise to different cell types in the animal body: the ectoderm forms the nervous system and the outer layer of skin, the mesoderm gives rise to muscles and connective tissues, and the endoderm gives rise to the lining of the digestive system and other internal organs.

• Superphylum Lophotrochozoa

  • Animals belonging to superphylum Lophotrochozoa are protostomes: the blastopore (or the point of involution of the ectoderm or outer germ layer) becomes the mouth opening to the alimentary canal.
  • The lophotrochozoans are triploblastic, possessing an embryonic mesoderm sandwiched between the ectoderm and endoderm found in the diploblastic cnidarians.