The term ectoderm, which is derived from the Greek ektos, meaning outside, and derma, meaning skin, refers to the first upper cotyledon. It forms the nervous system during development, as well as the skin in humans and also in animals.
What is the ectoderm?
During the so-called gastrulation, which is an essential part of development, the blastula, which consists of a single layer of cells, becomes a structure consisting of three different layers of cells. The blastula is the egg cell after fertilization by a sperm and after multiple cell division. These three cell layers that make up the blastula after gastrulation are called the ectoderm, the outer cell layer, the mesoderm, the inner cell layer, and the entoderm, the inner cell layer. The ectoderm forms the nervous system, sensory organs, skin, and teeth later in development. The mesoderm develops into the muscle tissue, skeleton, blood vessels, and connective tissue. The endoderm, on the other hand, forms the epithelium, liver, pancreas, and respiratory and digestive systems after the embryo has completed development. These three layers of cells are also called the cotyledons and are the basis from which the organs of humans and animals develop.
Anatomy and structure
The cotyledons consist of one cell layer each. However, the cells of the cotyledons thus also of the ectoderm are not yet specialized. They are preprogrammed to develop into a specific cell type. This is described as differentiation. This differentiation is controlled. Each cell contains the information into which cell type it should develop. Thus, the cells of the different cotyledons have different information for differentiation. Even within a cotyledon, the cells possess different information for differentiation. Therefore, different cell types form from each cotyledon. Like the ectoderm which forms the nervous system, but also the teeth. So the cells of the cotyledons are determined, they have a predefined differentiation pathway. However, it is possible for cells of one cotyledon to become cells of another cotyledon. This occurs during the formation of the mesoderm. This is then called transdetermination of the cell. It changes its original determinacy.
Function and tasks
Animals, and therefore humans, that form the three cotyledons are called bilaterally symmetrical animals. The blastula, or in humans sore higher mammals it is also called a blastocyst, is a type of hollow sphere that consists of a layer of cells. It first develops into the gastrula. During this process, the two primary cotyledons are formed. These are the outer ectoderm and the inner endoderm. At this stage of development, the entoderm forms the primordial mouth and the so-called primordial intestine. The mesoderm is formed slightly later. Rearrangements of the cells then occur during gastrulation. The cavity inside the sphere is filled more and more while the ectoderm closes the complete outside of the gastrula. Gastrulation then transitions into neurulation. This is the formation of the neural tube. The neural tube later forms the central nervous system when the developmental process is complete. The neural tube forms by remodeling the neuroectoderm. This forms from the ectoderm and then forms the neural tube by refolding the cell layer. First, the ectoderm thickens, which is induced by specific signals from the mesoderm. The neural plate forms. The edges of these plates form the neural bulges and form the neural groove between them. These neural ridges and the neural groove then form the neural fold, which eventually closes to form the neural tube. The front part of the neural tube forms the brain and the tube behind it forms the spinal cord. The cavity of the neural tube fills with cerebrospinal fluid. In addition, the eye vesicles, which later become the actual eyes, also form in the anterior region. This process is called the primary neurulation. Secondary neurulation, on the other hand, is the formation of the fluid-filled cavities in the areas that join the neural tube.
Diseases
Spina bifida is the malformation of the neural tube. This malformation can vary in severity.It occurs approximately between the 22nd and 28th day of the embryo‘s development. During this time, neurulation takes place, which is the formation of the neural tube by the neuroectoderm. Spina bifida refers to the defective closure or non-closure of the neural tube in the posterior part of the neural tube. Spina bifida manifests in distinctive forms. Spina bifida occulta is characterized by an absence of the spinal cord membrane, the meninges. This form of spina bifida is not externally recognizable. This form is not severe and does not require treatment. Spina bifida aperta, on the other hand, is characterized by a neural tube that is not completely closed. There are three forms of spina bifida aperta. Meningocele is a mild form of this condition. The spinal cord membranes bulge out and form cysts under the skin, which can be removed surgically. The spinal cord is not affected. Meningomyelocele is a severe form of spina bifida. The spinal column has one or more fractures that cause parts of the spinal cord to protrude from the spinal column. Damage to the nerves occurs. However, this can be treated surgically. Myeloschisis refers to the case where nerve tissue is completely exposed. This is thus the most severe case of spina bifida aperta.
