Delamination

The embryogenic Delamination corresponds to a process in which the cells of the blastula constrict 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 pathophysiology must be distinguished from delamination in the context of embryogenesis.

What is delamination?

Embryogenesis is a natural process with the goal of child development. It takes around eight weeks to complete and begins with the fertilization of the egg by a sperm. The end of embryogenesis changes into the beginning of fetogenesis.

Gastrulation is an important phase of embryogenesis and takes place in humans and all other multicellular animals. The blastula turns inside out during gastrulation. Three cotyledons are formed.

Gastrulation consists of several steps. In addition to invagination, involution, ingression, and epibolism, delamination is an essential part of the process. Literally translated, the Latin term "delamination" means something like "peeling off in layers". This means a constriction in which cells of the blastula constrict those of the prospective endoderm into the blastocoel. This process follows the ingression, i.e. the immigration of cells of the prospective endoderm. After the delamination, the epibolism takes place, with which the gastrulation comes to an end.

Although the entire process, including the delamination, is basically similar for all four-cell cells, the individual processes can differ more or less from species to species.

Function & task

With each delamination, two layers of cells are formed one on top of the other. The starting material is a single cell layer. The transformation of the individual layers into superimposed layers can be carried out either by cell division parallel to the layer plane, or by migration of individual cells. The latter is the case with gastrulation.

The term delamination can represent different processes in different contexts. In the context of embryogenesis, the emigration of cells is always meant, as is achieved by constriction. For mammals, the consequence of embryonic delamination is the formation of a cotyledon, which is also known as the endoderm. The endoderm corresponds to the interior of the three cotyledons and mainly contains the tissue of the later gastrointestinal tract.

For many mammals, the tissue of the endoderm also forms parts of digestive glands such as liver and pancreas, parts of the respiratory tract, parts of the thyroid, urinary bladder tissue and urethral tissue through differentiation processes.

The endoderm, like the other two cotyledons, is a cluster of tissue that arises from the multipotent cells of the zygote after fertilization through the first cell division. Ultimately, the multipotent cells lose more and more of their multipotency during embryogenesis and receive ever closer specialization until they correspond to organ-specific tissues. Delamination contributes to these processes.

On the lower side of the embryonic node, delamination creates the entoderm for many mammals, which grows along the trophoblast to the opposite pole. The primary yolk sac then arises extra-embryonic. After this delamination, the bilayered germinal vesicle consists on the outer side of the ectoderm including trophoblasts. On the inside, however, it consists of endoderm.

In some animals, among other things, the tissues of the abdominal cord are created by delamination from the neuroectoderm. In the avian embryo, the hypoblast is also created by delamination processes. Arthur Hertig compared the delamination processes of human embryonic development with the subdivisions of a soap bubble early on. Delamination results in cells of the envelope mesoblast from the trophoblast, which attach to the outer wall of the membrane-covered yolk sac.

The sequence of the delamination process, which is best known from a human point of view, is a constriction. Blastula cells tie off the future endoderm cells in the blastocoel.

Illnesses & ailments

The early development of the human embryo affects the first two weeks. During this time, the germ is largely insensitive to damaging influences. Malformations and chromosomal aberrations can lead to an unnoticed abortion during this time.

The primitive streak forms two weeks after a human egg is fertilized. The embryo is particularly sensitive to harmful influences during the subsequent gastrulation. Delamination processes, for example, can be disturbed by the influence of pollutants. The consequences of such a disorder can be miscarriages. This happens when the unborn child is not viable from the outset due to developmental defects.

In contrast, the term delamination is used in pathophysiology for different pathology processes and in the context of various clinical pictures. For example, Marfan's syndrome is associated with symptoms of the cardiovascular system. One of the most common symptoms is delamination of the aortic walls, which can cause the artery to rupture.

In pathophysiology, delamination can also be related to bones, tendons and joints, so that in the context of various clinical pictures, for example, we can speak of delamination of the knee joint. This use of the term in pathophysiology must be clearly distinguished from the use of the term in the context of embryonic development. For Marfan syndrome, for example, this means that the clinical picture is not caused by delamination disorders in the sense of embryonic development disorders.