Index
hat is it? is one of the three germ layers of the group of cells that fuse early during embryonic life.
It appears in all animals, except perhaps sponges, and from which organs and tissues are formed.
As an embryo develops, a single fertilized cell progresses through multiple rounds of cell division.
Eventually, the group of cells goes through a stage called gastrulation, during which the embryo is reorganized into the three germ layers: endoderm, ectoderm and mesoderm.
After gastrulation, the embryo goes through a process called neurulation, which initiates the development of the nervous system.
During neurulation, the ectoderm is differentiated into two parts. The first is the superficial ectoderm, which gives rise to tissues on the external surface of the body such as the epidermis, hair and nails.
The second is the neuroectoderm, which forms the nervous system of the embryo.
The neuroectoderm is further divided into the neural tube, which acts as a precursor to the central nervous system of the embryo, and in the neural crest, a collection of mobile cells expelled from the junction between the neural tube and the epidermis after tube formation neural.
The neural crest helps to form many of the bones and connective tissues of the head and face, as well as parts of the peripheral nervous system. In fish, the neural crest helps form the dorsal fins, and in the turtles it is useful from the carapace.
In 1817 Christian Pander , a PhD student at the University of Würzburg, in Würzburg, Germany, discovered the germ layers in chicken embryos, Gallus gallus.
Within his dissertation, Pander described how two layers of cells, which he called serous and mucosal layers, give rise to a third layer, which he called the vascular layer.
Pander thus described the process of gastrulation in the chicken, and he brought the three layers of the embryo to the attention of the scientific community.
In 1825, the physician and embryologist Martin Rathke, in Prussia (later Poland), discovered cellular layers in the developing crab, Astacus astacus, which corresponded to the serous and mucosal layers of Pander.
The results of Rathke showed that these two layers of cells existed in the embryos of non-vertebrate animals.
Endodermo
We can not talk about the ectoderm without understanding what is the endoderm and the mesoderm. The endoderm is the innermost layer of primary germ cells that form in early embryos.
The endoderm begins with flattened cells, but then the forms become columnar cells.
They form the epithelial linings of many organs and systems of the body mainly in the digestive tract, and cover the vast majority of the gastrointestinal tract excluding the mouth, pharynx and anus.
In addition, the respiratory system, the endocrine system, the auditory system and the urinary system are also coated in different proportions in general by the differentiated endodermal germ cells of the early embryo.
However, particularly the alveoli, trachea and bronchi of the respiratory system are of endodermal origin.
On the other hand, the follicles of the thyroid gland and the endocrine system, the epithelium of the auditory tube and the tympanic cavity of the auditory system, the urinary bladder and the urethra of the urinary system are aligned through the differentiation of the endodermal germ cells.
All these cells, organs and systems are formed at different times during the embryonic stage of any particular animal.
Since there are many bodily systems that have endodermal origin, the importance of the particular layer of germ cells is very high and any malfunctioning with that could cause serious consequences.
Mesodermo
The mesoderm is the germinal layer that distinguishes evolutionarily higher life forms from lower life forms with radial symmetry of the body.
The mesoderm allows higher life forms to have an internal body cavity in which the organs can reside, protected from the movements and shaking of the outer layers of the body by fluids and connective tissue.
Joint function
The ectoderm and the endoderm together with the mesoderm are the layers of the primary germ cells of any animal.
All the organs and the system of the body are based exclusively on these three cellular layers, and the ectoderm and the endoderm together represent more than two thirds of the organs of the body.
The location in relation to each other has been the basis for naming the germ cell layers during the early stages of embryonic development.
Some comparisons between these cell layers
- Ectoderm is the outermost layer of the primary germ cells, but the endoderm is the innermost layer of the early embryo.
- Both layers of cells cover some common and separated organs, but the endoderm never covers any organ exposed to the outside.
- Few genes are required to form the ectoderm, but most of the genes in the genome are required to form the endoderm.
- The cells of the endoderm are mostly columnar, while there is no particular form or they have almost all the cell forms in the ectodermal cells after differentiation.
Scientific potential
Due to the enormous capacity of these germinal layers to differentiate themselves in a great variety of organs and tissues, they attract a lot of attention from scientists who seek to determine how humans develop.
In stem-cell jargon, a pluripotent stem cell can be converted into any of the three germ layers. Multipotent stem cells can result in lineages restricted to a dermal layer, or even to a lineage within a dermal layer.
For example, it should be possible to derive a mesoderm stem cell and guide its differentiation into a new bone, such as a femur, for a patient with a congenital defect, or develop a new bone marrow for a patient with lymphoma.
