Embryogenetic delamination corresponds to a process in which the cells of the blastula cut off the cells of the future endoderm into the blastocoel. Delamination is a step in gastrulation and is related to cotyledon formation. Delamination in the context of embryogenesis must be distinguished from delamination in the context of pathophysiology.
What is delamination?
Delamination is a step in gastrulation, and this in turn is an important phase of embryogenesis. Embryogenesis is a natural process with the goal of child development. It takes a period of about eight weeks and begins with the fertilization of the egg by a sperm. The end of embryogenesis transitions into the beginning of fetogenesis. Gastrulation is an important phase of embryogenesis and occurs in humans as well as all other multicellular animals. The blastula inverts during gastrulation. Three cotyledons form during this process. Gastrulation is composed of several steps. In addition to invagination, involution, ingression, and epiboly, delamination is an essential part of the process. Literally translated, the Latin term “delamination” means something like “layer-by-layer detachment.” This refers to a strangulation in which cells of the blastula strangulate those of the prospective endoderm into the blastocoel. This process follows ingression, which is the immigration of cells of the prospective endoderm. After delamination, epiboly takes place, with which gastrulation comes to an end. Although the entire process, including delamination, is similar in principle in all four-cell organisms, the individual processes may differ to a greater or lesser extent from species to species.
Function and task
In each delamination, two superimposed layers of cells are formed. The starting material is a single cell layer. Transformation of the single layer into superimposed layers can be accomplished either by cell division in parallelism with the layer plane, or by emigration of single cells. The latter is the case in gastrulation. The term delamination can reflect different processes in different contexts. In the context of embryogenesis, it always refers to the emigration of cells, as achieved by strangulation. For mammals, the consequence of embryonic delamination is the formation of a cotyledon, also known as the endoderm. The entoderm corresponds to the inner of the three germ layers and contains mainly the tissue of the later gastrointestinal tract. For many mammals, parts of digestive glands such as liver and pancreas, respiratory tract parts, thyroid gland parts, urinary bladder tissue, and urethral tissue also form from the tissue of the entoderm through differentiation processes. The endoderm, like the other two cotyledons, is a tissue cluster that develops from the multipotent cells of the zygote after fertilization by initial cell division. Eventually, during embryogenesis, the multipotent cells lose more and more multipotency and acquire narrower and narrower specialization until they correspond to organ-specific tissues. Delamination contributes to these processes. On the lower side of the embryonic node, delamination gives rise to the endoderm for many mammals, which grows along the trophoblast to the opposite pole. Extraembryonically, the primary yolk sac then develops. After this delamination, the two-layered germinal vesicle consists on the outer side of ectoderm including trophoblasts. On the inner side, however, it consists of endoderm. In some animals, the tissues of the abdominal cord, among others, are formed by delamination from the neuroectoderm. In the avian embryo, the hypoblast is also formed by processes of delamination. Arthur Hertig early on compared the delamination processes of human embryonic development to subdivisions of a soap bubble. Delamination gives rise to cells of the envelope mesoblast from the trophoblast, which attach to the outer wall of the membrane-enveloped yolk sac. The sequence of the most familiar delamination process in human genetics is strangulation. Blastula cells thereby strangulate the future endoderm cells into the blastocoel.
Diseases and disorders
Early development of the human embryo involves the first two weeks. During this period, the germ is largely impervious to damaging influences.Malformations and chromosomal aberrations can cause an unnoticed abortion during this time. Two weeks after fertilization of a human egg, the primitive streak is formed. Especially during the subsequent gastrulation, the embryo is highly sensitive to harmful influences. For example, processes of delamination can be disturbed by the influence of harmful substances. The consequences of such a disturbance can be miscarriages. This occurs when the unborn child is not viable from the beginning due to the developmental defects. The term delamination, on the other hand, is used in pathophysiology for different pathological processes and in the context of different clinical pictures. For example, Marfan syndrome is associated with symptoms of the cardiovascular system. One of the most common symptoms is delamination of the aortic walls, which can cause rupture of the artery. Delamination in pathophysiology can also be referred to bones, tendons, and joints, so that in the context of different clinical pictures, we can speak of delamination of the knee joint, for example. This use of the term in pathophysiology must thus be clearly distinguished from the use of the term in the context of embryonic development. This means, for example, for Marfan syndrome that the clinical picture is not caused by delamination disorders in the sense of embryonic developmental disorders.
