Invagination: Function, Role & Diseases

The term intussusception is used in medicine to refer to any type of invagination. This includes invagination of intestinal segments in infants and young children, phagocytosis in the immune response, or invagination of the blastocyst in embryogenesis. In embryogenesis, invagination represents the onset of gastrulation.

What is intussusception?

A very early stage of embryogenesis is described by the process of invagination. The main process is invagination of the blastula or blastocyst. In medicine, the term invagination is widely used. Most often, it is used to describe the invagination of one section of intestine into another. In this case, parts of the small intestine may invaginate into sections of the large intestine or into other sections of the small intestine. The invaginated sections of intestine are cut off from the blood supply and may die. The symptoms of intestinal obstruction then develop. This form of intussusception occurs mainly in infants and young children up to two years of age. However, adults can also suffer from it in the case of morphological peculiarities or in the presence of tumors. Only surgery can eliminate the life-threatening condition of this particular intestinal obstruction. A completely different form of intussusception is phagocytosis. In this process, the so-called phagocytes, the scavenger cells, surround bacteria or viruses and break them down. In addition to antibodies, they perform an important function for the immune system. In embryogenesis, a third form of invagination describes the formation of the cotyledons from the blastocyst. Here, invagination initiates the process of gastrulation.

Function and task

A very early stage of embryogenesis is described by the process of invagination. The main process is the invagination of the blastula or blastocyst, from which two to three cotyledons are then formed. The blastula is also called the blastocyst and represents a hollow sphere filled with fluid. This process occurs at an early embryonic stage in most multicellular animals. In higher mammals and humans, a blastocyst rather than a blastula develops. Unlike the blastula, the blastocyst has a cluster of cells at one point in the hollow sphere, from which the embryo later differentiates. The trophoblast forms from the blastocyst shell, from which embryonic accessory organs (placenta) develop. The interior of the blastocyst is comparable to the interior of the yolk sac of birds, reptiles, and cloacal animals. However, the blastula is simply a hollow body filled with fluid. Therefore, the blastocyst can be contrasted with the blastula. The blastula or blastocyst initially forms via the process of blastulation. This process of blastocyst formation is completed after a few days of early embryogenesis. After that, gastrulation begins. During gastrulation, the cotyledons form from the blastocyst. Basically, this process is similar in all animals. Nevertheless, there are significant differences in the concrete processes and the results in the individual animal species. With gastrulation, the conditions for the development of the internal organs are created by the formation of the cotyledons. All bilaterally symmetrical animals form three cotyledons during embryogenesis and all others only two cotyledons. In bilaterally symmetrical animals, the left half of the body represents the mirror image of the right half of the body and vice versa. Nonbilaterally symmetrical animals include the jellyfish and the cnidarians. Despite differences in the course of gastrulation, important basic processes take place that apply to all multicellular animal species. Initially, invagination into the interior of the hollow sphere occurs at a site on the bladder germ. This process represents the actual invagination. The invaginated part develops into an inner shell, forming a bivalved gastrula. The outer shell is called the ectoderm and the inner shell is called the endoterm. The inner cavity represents the primary body cavity. The invaginated area, which presents as a dent and develops into the endoterm, can be considered the primordial intestine. Invagination is followed by curling of the future endoderm, which is also called involution. With ingression, cells of the future endoderm migrate in.This is followed by delamination, in which the future endoderm is cut off in the blastocoel. The endoderm shows an opening to the outside, which is also called the primordial orifice. As mentioned earlier, the endoterm itself represents the primordial intestine. In higher mammals and humans, the primordial mouth develops into the anus. The true mouth breaks through on the other side of the blastula. After the 14th day of gestation, the third cotyledon (the mesoderm) forms from the ectoderm by migrated cells over the primitive streak. A layer of cells forms between the ectoderm and the entoderm.

Diseases and disorders

Within the first two weeks of human germ development, which includes invagination, the fetus is impervious to environmental influences. If the germ develops incorrectly, an unnoticed abortion usually occurs. With the formation of the primitive streak, a groove-like thickening on the ectoderm, the threat to the germ becomes particularly great. At this stage of development, each organ goes through specific phases that make it sensitive to any environmental influences such as chemicals, radiation or viruses. If these occur, organ malformations often result. A typical example is the clinical picture of sirenomelia. Sirenomelia is characterized by the fusion of the legs starting at the pelvis. Furthermore, the kidneys are usually missing, so that the child is not viable. Another example is the so-called coccygeal teratoma, which is a usually benign but often child’s head-sized coccygeal tumor.