ectoderm


Also found in: Dictionary, Thesaurus, Medical, Wikipedia.
Related to ectoderm: mesoderm

ectoderm,

layer of cells that covers the surface of an animal embryo after the process of gastrulation has occurred. This outer layer, together with the endodermendoderm
, in biology, inner layer of tissue formed in the gastrula stage of the developing embryo. At the end of the blastula stage, cells of the embryo are arranged in the form of a hollow ball.
..... Click the link for more information.
, or inner layer, is present in all early embryos. In the development of animals of the phyla PoriferaPorifera
[Lat.,=pore bearer], animal phylum consisting of the organisms commonly called sponges. It is the only phylum of the animal subkingdom Parazoa and represents the least evolutionarily advanced group of the animal kingdom.
..... Click the link for more information.
, CtenophoraCtenophora
, a small phylum of exclusively marine, invertebrate animals, commonly known as comb jellies. Because they are so delicate that specimens are difficult to collect, little was known about them until the advent of blue-water scuba and submersible collecting.
..... Click the link for more information.
, and CnidariaCnidaria
or Coelenterata
, phylum of invertebrate animals comprising the sea anemones, corals, jellyfish, and hydroids. Cnidarians are radially symmetrical (see symmetry, biological).
..... Click the link for more information.
, these two primary layers give rise to all the tissues and organs of the animals, a process known as diploblastic development. In higher animals, such as those of the phyla EchinodermataEchinodermata
[Gr.,=spiny skin], phylum of exclusively marine bottom-dwelling invertebrates having external skeletons of calcareous plates just beneath the skin. The plates may be solidly fused together, as in sea urchins, loosely articulated to facilitate movement, as in sea
..... Click the link for more information.
 and ChordataChordata
, phylum of animals having a notochord, or dorsal stiffening rod, as the chief internal skeletal support at some stage of their development. Most chordates are vertebrates (animals with backbones), but the phylum also includes some small marine invertebrate animals.
..... Click the link for more information.
, a third, middle layer, the mesodermmesoderm,
in biology, middle layer of tissue formed in the gastrula stage of the developing embryo. At the end of the blastula stage, cells of the embryo are arranged in the form of a hollow ball.
..... Click the link for more information.
, is formed between the ectoderm and endoderm during gastrulation, and the process is termed triploblastic development. In most embryos, differentiation of ectodermal tissue gives rise to epidermis and its specialized structures (scales, feathers, nails, and hair); some exocrine glands (sweat and sebaceous glands); some endocrine glands (the pineal body and the pituitary gland); the nervous system; and the organs of special sense (ear and eye). In animals of some phyla, such as the MolluscaMollusca
, taxonomic name for the one of the largest phyla of invertebrate animals (Arthropoda is the largest) comprising more than 50,000 living mollusk species and about 35,000 fossil species dating back to the Cambrian period.
..... Click the link for more information.
 and AnnelidaAnnelida
[Lat., anellus=a ring], phylum of soft-bodied, bilaterally symmetrical (see symmetry, biological), segmented animals, known as the segmented, or annelid, worms.
..... Click the link for more information.
, the fate of particular cells of the embryo is determined in the earliest stages of the fertilized egg and may even be fixed at or before fertilization.

Ectoderm

 

(1) The outermost germ layer; the external layer of the embryo of multicellular animals in the gastrular stage. From the ectoderm are formed the integuments, nervous system, sensory organs, anterior and posterior sections of the digestive tract, external gills, and ectomesenchyme. In the Deuterostomia, all the elements derived from the ectoderm are formed as a result of the action upon it of the chordomesoderm, the entoderm, and their derivatives.

(2) The external wall of the body of coelenterates. The ectoderm consists of a single layer of cells—epithelial, epithelio-muscular, interstitial, and sensory cells, as well as stinging capsules.

ectoderm

[′ek·tə‚dərm]
(embryology)
The outer germ layer of an animal embryo. Also known as epiblast.
(invertebrate zoology)
The outer layer of a diploblastic animal.
References in periodicals archive ?
The binary character model allows an assessment of the history of any structural elaboration of ectoderm between the post-oral arms and does not distinguish between degrees of elaboration.
Sp-Smad2/3 mediates patterning of neurogenic ectoderm by nodal in the sea urchin embryo.
Namely, Wnt6 is expressed in the neural plate border at the onset of neurulation (E4) and in the dorsolateral edges of the forming neural tube at E5 (neural crest progenitor region), whereas Wnt8 is absent from a neural plate border at E4 but at E5 is expressed in the non-neural ectoderm, directly adjacent to the neural crest progenitor region.
of cases Percentage Post auricular 2 33.3% Parotid 2 33.3% Pre auricular 1 16.7% Over the maxilla 1 16.7% DISCUSSION: Epidermoid are derived from ectoderm, but they are inclusion cysts that are lined only by squamous epithelium.
In Physalia, the cnidosacs are more hemispherical and the ectoderm thinner than Porpita.
After formaldehyde was applied, a fluorescent stain appeared in cells of the ectoderm or at their surface.
But he believes that other genes may possibly serve as markers for selecting lines primed for mesoderm and ectoderm development.
This value corresponds to the thickness of the anal plate ectoderm. The relationship between the degree of invagination and the position of the boundary is shown in Figure 4.
Within the larva, a new nervous system forms from the ventral ectoderm in close proximity to the water vascular system (MacBride, 1907; Narasimhamurti, 1933; Olsen, 1942).
Cholesteatoma or epidermoid cyst is a cystic mass-like lesion originating from the aberrant ectoderm trapped within the petrous apex.
The embryological development of the human eye involves a series of events, beginning with fertilization of the ovum and continuing through the early postnatal period, in three embryonic layers: neural ectoderm, neural crest, and surface ectoderm, with minor contribution from the mesoderm.
These glands develop from an early structure called the oral ectoderm, but the actual process is not fully understood.