Intussusception (in embryogenesis)

The term Intussusception is used in medicine for all kinds of invaginations. This affects, among other things, the invagination of intestinal sections in infants and small children, phagocytosis in the immune reaction or the invagination of the blastocyst in embryogenesis. In embryogenesis, intussusception is the beginning of gastrulation.

What is the intussusception?

The term intussusception is widely used in medicine. Mostly it is used to invade one section of the intestine into another. Parts of the small intestine can invade into sections of the large intestine or into other sections of the small intestine. The everted intestinal sections are cut off from the blood supply and can die. The symptoms of an intestinal obstruction then develop. This form of intussusception occurs mainly in infants and young children up to two years of age.

However, adults with morphological peculiarities or the presence of tumors can also develop it. The life-threatening condition of this particular intestinal obstruction can only be removed through an operation.

Phagocytosis is a completely different form of intussusception. The so-called phagocytes enclose the scavenger cells, bacteria or viruses and decompose them. In addition to the antibodies, they play an important role in the immune system.

A third form of intussusception describes the formation of the cotyledons from the blastocyst during embryogenesis. Here intussusception initiates the process of gastrulation.

Function & task

A very early phase of embryogenesis is described by the process of intussusception. The main process is the intussusception of the blastula or blastocyst, from which two to three cotyledons are formed. The blastula is also known as the germ of the bladder and is a hollow sphere filled with fluid. This process takes place in the early embryonic stage of most multicellular animals.

In higher mammals and humans, a blastocyst rather than a blastula develops. In contrast to the blastula, the blastocyst has a cluster of cells at one point on the hollow sphere, from which the embryo later differentiates. The trophoblast forms from the blastocyst envelope, from which embryonic auxiliary organs (placenta) develop.

The interior of the blastocyst is comparable to the interior of the yolk sac of birds, reptiles and monotons. 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 through the process of blastulation. This process of bladder germ formation is complete after a few days of early embryogenesis.

After that, gastrulation begins. During gastrulation, the cotyledons develop from the bladder germ. Basically, this process is similar in all animals. Nevertheless, there are clear differences between the individual animal species in terms of the specific processes and results. With gastrulation, the conditions for the development of the internal organs are created through the emergence of the germ layers. All bilaterally symmetrical animals develop three cotyledons during embryogenesis and all others only two cotyledons. In bilaterally symmetrical animals, the left half of the body is the mirror image of the right half of the body and vice versa. The non-bilaterally symmetrical animals include the jellyfish and the cnidarians.

Despite differences in the gastrulation process, important fundamental processes take place that apply to all multicellular animal species. At the beginning, there is an invagination into the interior of the hollow sphere at one point on the bladder germ. This process represents the actual intussusception. The invaginated part develops into an inner shell, so that a two-shell gastrula is created. The outer shell is called the ectoderm and the inner shell is called the endoterm. The inner cavity represents the primary body cavity. The inverted area, which presents itself as a dent and develops into the endoterm, can be regarded as the primeval intestine.

After the intussusception, the future endoderm rolls in, which is also known as involution. With the ingression, cells of the future endoderm migrate. This is followed by delamination, in which the future endoderm in the blastocoel is pinched off. The endoderm shows an opening to the outside, which is also known as the original mouth. As already mentioned, the endoterm itself represents the primitive intestine. In higher mammals and humans, the primordial mouth develops into the anus. The real mouth breaks through on the other side of the blastula.

After the 14th day of pregnancy, the third cotyledon (the mesoderm) is formed by immigrated cells over the primitive streak from the ectoderm. A layer of cells forms between the ectoderm and endoderm.

Illnesses & ailments

Within the first two weeks of human germ development, which also includes intussusception, the fetus is insensitive to environmental influences. If the germ develops incorrectly, it usually leads to an unnoticed abortion. With the formation of the primitive streak, a channel-like thickening on the ectoderm, the risk to the germ becomes particularly great.

At this stage of development, every 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 occur. A typical example is the sirenomelia. Sirenomelia is characterized by the growing together of the legs from the pelvis. Furthermore, the kidneys are usually missing, so that the child is not viable. Another example is the so-called tailbone teratoma, which is a mostly benign but often the size of a child's head, tailbone tumor.