Ectoderm outer. The meaning of the word ectoderm in the encyclopedia of biology

The doctrine of germ layers, one of the main generalizations in embryology, played big role in the history of biology.

In 2000, Canadian embryologist Brian Keith Hall proposed that the neural crest be considered nothing more than a separate fourth germ layer. This interpretation quickly spread in the scientific literature.

In all animals, the same organs are obtained from the same germ layer. The ectoderm gives the outer coverings and the nervous system. It is formed from the endoderm most of digestive tract and digestive glands (in vertebrates - the liver, pancreas, and lungs). The mesoderm forms the rest of the organs: muscles, lining of the secondary body cavity, organs of the circulatory, excretory and reproductive systems, in vertebrates and echinoderms - the internal skeleton. (It must be borne in mind that most of the organs of an adult animal include tissues originating from two or all three germ layers.) A very important conclusion follows from this: in all animals, the main organ systems have a common origin, and they can be compared. For example, central nervous system has a common origin in the sense that in evolution it originates from the subcutaneous nerve plexus, similar to the nervous network of the hydra, and in ontogenesis - from the outer germ layer.

germ layers (lat. embryonic folia), germ layers, layers of the body of the embryo of multicellular animals, formed during gastrulation and giving rise to various organs and tissues. Most organisms have three germ layers:

• outer - ectoderm,
• internal - endoderm,
• middle - mesoderm.

Derivatives of the ectoderm perform mainly integumentary and sensitive functions, derivatives of the endoderm - the functions of nutrition and respiration, and derivatives of the mesoderm - connections between parts of the embryo, motor, support and trophic functions.

The same germ layer in representatives of different classes of vertebrates has the same properties, i.e. germ layers are with homologous formations and their presence confirms the position of the unity of the origin of the animal world. Germ layers are formed in embryos of all major classes of vertebrates, i.e. are universally distributed.

The germ layer is a layer of cells that occupies a certain position. But it cannot be considered only from topographic positions. The germ layer is a collection of cells that have certain development trends. A clearly defined, albeit rather wide, range of developmental potentials is finally determined (determined) by the end of gastrulation. Thus, each germ layer develops in a given direction, takes participation in the emergence of the rudiments of certain organs.

Throughout the animal kingdom, individual organs and tissues originate from the same germ layer. From the ectoderm, the neural tube and integumentary epithelium are formed, from the endoderm - intestinal epithelium, from the mesoderm - muscle and connective tissue, epithelium of the kidneys, gonads, serous cavities. From the mesoderm and the cranial part of the ectoderm cells are evicted, which fill the space between the sheets and form the mesenchyme. Mesenchymal cells form syncytium: they are connected to each other by cytoplasmic processes. The mesenchyme forms the connective tissue.

Each individual germ layer is not an autonomous formation, it is part of the whole. The germ layers are able to differentiate only by interacting with each other and being under the influence of the integrating influences of the embryo as a whole. A good illustration of such interaction and mutual influence are experiments on early gastrulae of amphibians, according to which the cellular material of the ecto-, ento- and mesoderm can be forced to radically change the path of its development, to participate in the formation of organs that are completely uncharacteristic of this leaf. This suggests that, at the beginning of gastrulation, the fate of the cellular material of each germ layer, strictly speaking, is not yet predetermined. The development and differentiation of each leaf, their organogenetic specificity, is due to the mutual influence of the parts of the whole embryo and is possible only with normal integration.

Ectoderm is part of any animal multicellular organism. Only in some this structure is preserved only during the period, while in others - throughout life. What is an ectoderm?

Types of germ layers

During ontogenesis, a fertilized egg divides many times, forming several layers of cells over time. In the process of their differentiation, several layers of the body are formed, from which tissues, organs and their systems will subsequently form. Ectoderm is the outer germ layer. During the development of the zygote, it is formed first from the inner layer of the embryo called the endoderm. Subsequently, the respiratory and digestive systems develop from it. From the middle germ layer - the mesoderm - organs are formed that, as it were, bind the whole organism together. These are muscles and ligaments, the internal skeleton, the reproductive, circulatory and excretory systems.

Ectoderm derivatives

The ectoderm is the germ layer, from the cells of which the integuments and organs of the nervous system are formed. Its formation occurs at the gastrula stage. The nervous system of vertebrates is characterized by a high level of development. It consists of the brain and spinal cord, as well as individual fibers that extend from them to all structures of the body. The sense organs and sensory systems are also derivatives of the ectoderm. Since this germ layer develops from the outer layer of cells, it forms integuments. First of all, it is the epithelial tissue of the skin and the digestive system.

Hydra ectoderm

In coelenterates, the ectoderm is the layer of the body that persists throughout life. Consider its structure with an example freshwater hydra. This is a two-layer animal, the body of which is formed by ecto- and endoderm. Between them is a dense plate of intercellular substance. Ectoderm cells are diverse in structure and function. For the first time in the course of evolution, such specialized structures appear precisely in

The composition of the ectoderm includes skin-muscle cells that are capable of contraction. Thanks to them, the hydra moves like an acrobat, turning over from the sole to the tentacles. When exposed to nerve cells, which are also located in the outer layer of the body, the animal shrinks. This is how their reflex activity manifests itself. The outer layer also contains intermediate cells that can transform into any other types. It determines high level regeneration of freshwater hydra. She can completely restore her body even from a mushy state.

What are stinging cells

The ectoderm is the outer layer, which serves as a reliable defense and means of hunting. This function is performed. They consist of a capsule with a thread twisted inside. When the victim swims by, she touches a sensitive hair. As a result, the stinging thread unwinds and digs into her body with force. Poisonous substances are introduced along with it. The paralyzed victim, with the help of tentacles, is in the intestinal cavity, where it is digested. Many are dangerous to humans. The action of their stinging cells causes severe burns, disruption of the heart and respiratory system and sometimes even ends in death.

So, the ectoderm is the outer germ layer, from which, in the process of crushing in vertebrates, the integuments of the body and organs of the nervous system are formed. In coelenterates, the ectoderm forms a number of specialized cells: skin-muscular, intermediate, nervous and stinging.

The section is very easy to use. In the proposed field, just enter right word, and we will give you a list of its values. It should be noted that our site provides data from different sources- encyclopedic, explanatory, derivational dictionaries. Here you can also get acquainted with examples of the use of the word you entered.

The meaning of the word ectoderm

ectoderm in the crossword dictionary

Dictionary of medical terms

ectoderm (ectoderm, LNE; ecto- + Greek derma skin)

outer germ layer of a three-layer embryo; E.'s derivatives are the epidermis, the nervous system, and, to a large extent, the sense organs.

Encyclopedic Dictionary, 1998

ectoderm

ECTODERM (from ecto... and dermis)

outer germ layer of multicellular animals. From the ectoderm, the skin epithelium, nervous system, sensory organs, anterior and posterior intestines are formed. Wed Endoderm, Mesoderm.

The outer layer of the body wall in coelenterates.

ectoderm

E., or the outer germ layer, the outer layer of the embryo of multicellular animal organisms at the gastrula stage. From E. in the process of development of the embryo, integuments, the nervous system, sensory organs, the anterior and posterior sections of the digestive system, external gills, and also ectomesenchyme are formed. In deuterostomes, all derivatives of E. are formed as a result of induction influences on it by the chordomesoderm, endoderm, and their derivatives.

The outer wall of the body of intestinal animals, consisting of one layer of cells: epithelial, epithelial-muscular, intermediate (interstitial), sensitive (nerve), and also stinging.

Wikipedia

ectoderm

ectoderm- outer germ layer of the embryo early stages development. There is also a middle germ layer - the mesoderm and the germ layer furthest from the ectoderm - endoderm. In the embryo, it is formed first and is formed from the outer layer of germ cells. The ectoderm forms the nervous system (in vertebrates: spinal cord, peripheral nerves, and brain), tooth enamel, and epidermis. It also forms the sense organs, the epithelium of the anterior and posterior sections of the digestive system.

In vertebrates, the ectoderm consists of three parts: the outer ectoderm, the neural crest, and the neural tube. The neural crest and neural tube are also known as the neuroectoderm. Formed at the gastrula stage.

Examples of the use of the word ectoderm in the literature.

Beatrice-Joanna could no longer think of any other obligation than her debt to this one inch of protest, weighing thirty-something grains, whose cells were continually dividing and multiplying - ectoderm, mesoderm, endoderm - protesting, protesting and protesting again.

In these complex organisms, two membranes are distinguished - the endoderm and ectoderm, slightly different from one another, one of them serves to form the digestive sac, the other is the outer shell of the body.

The skin relief is formed at the 9-12th week of intrauterine development from ectoderm- the same embryonic layer from which the central nervous system develops.

ectoderm- the outer germ layer, from which the skin epithelium, nervous system, sensory organs, anterior and posterior intestines are formed.

ECTODERM [ectoderm(LNE); Greek ektos outside, outside + derma skin] - the outer germ layer of the body of the embryo, formed during gastrulation.

In the embryos of all multicellular animals, the primary ectoderm, or epiblast, occurs in the first phase of gastrulation (see). In higher vertebrates, including humans, the ectoderm itself, or secondary ectoderm, becomes that part of the epiblast that remains outside after the isolation of the mesoderm and the release of cellular material, giving rise to the notochord in the second phase of gastrulation.

The secondary ectoderm already during gastrulation is divided into three parts: neuroectoderm (or neural rudiment), represented by the neural plate, skin ectoderm and non-embryonic ectoderm.

The neural plate flexes to form the neural groove. The edges of the groove (neural folds) close, forming the neural tube, which is the rudiment of the spinal cord and brain. When the neural tube is closed, the so-called neural crest is formed, which forms two ganglionic plates on the sides of the neural tube. The tissue derivatives of the neural crest are neurons of sensory and autonomic (sympathetic) nodes, all peripheral neuroglia, chromatophores (pigment cells), and chromaffin tissue of the adrenal glands. Part of the mesenchyme also arises from the cells of the neural crest (see) - the ectomesenchyme. The neuroectoderm also includes small isolated islands of the neural rudiment localized in the skin ectoderm of the head (the so-called placodes). These include the rudiments of sensitive nodes of the cranial (cranial, T.) nerves, including the statoacoustic, or "auditory", placode - the rudiment of the membranous labyrinth of the inner ear and associated nodes of the vestibulocochlear nerve, as well as the lens placode - the area ectoderm, which forms the rudiment of the lens.

The skin ectoderm is the rudiment of the epithelium of the skin (epidermis) and its derivatives - the sebaceous and sweat glands, hair, nails, and in mammals also claws, hooves, horns, in birds - beak, feathers. In the region of the oral and anal bays of the embryo, the ectoderm invaginates towards the anterior and posterior ends of the midgut. These invaginations break into the cavity of the midgut, forming, respectively, the anterior and hindgut. The lining of the foregut, arising from the material of the ectoderm and prechordal plate, gives rise to the development of the epithelium. oral cavity, larynx, trachea, bronchi, thymus, thyroid, parathyroid glands, anterior pituitary, pharynx, esophagus. The epithelium develops from the ectodermal lining of the hindgut. Bladder, ureter, parts of the rectum.

The extra-embryonic ectoderm, which is a continuation of the skin ectoderm, is part of the temporary germinal organs, including the germinal membranes, and forms the outer epithelium of the serous membrane, the amnion epithelium, in the embryos of higher vertebrates (see Embryo, Fetal membranes). In mammals and humans, a part of the extra-embryonic ectoderm already at the beginning of the crushing of a fertilized egg is isolated in the form of a trophoblast (see).

Bibliography: Klishov A. A. Histogenesis and tissue regeneration, L., 1984; Knorre A. G. Embryonic histogenesis, L., 1971; Stanek I. Human embryology, trans. from Slovak, Bratislava, 1977.

A. G. Knorre, A. A. Klipov.