Critical layer thickness
The critical layer thickness is a cell biological term and, in multicellular organisms, describes the depth within a cell cluster from which the supply of the cells with nutrients becomes problematic.
properties
For single-celled organisms, for example amoebas , supply and disposal are usually relatively easy to secure: The extracellular space is much larger than the cell volume and the energy supply is therefore much greater than the energy consumption. In addition, the paths for the exchange of substances are very short. The cells can often move or create currents in the medium surrounding them with eyelashes.
In contrast, in all higher living beings, many cells are densely packed together. The spaces between neighboring cells, the interstitium , are often only nanometers wide. Accordingly, the volume of the nutrient medium that surrounds a single cell in the cluster is very small in relation to the cell volume and the energy supply in the immediate vicinity of the cell is much smaller than its energy requirement. The extracellular medium must therefore be constantly renewed. This material transport takes place mainly by diffusion in the direction of a concentration gradient . However, the transport routes and the time required for the transport become longer and longer, the deeper a cell lies inside the cell cluster. From a layer thickness of approx. 1 mm, the so-called critical layer thickness, the cells consume more energy per time than can be supplied, so that they perish due to a lack of nutrients and oxygen. A contributing factor to this development is that disposal is also becoming increasingly difficult.
In larger cell groups, the critical layer thickness is exceeded by far. The survival of the cell cluster is then made possible by the fact that a kind of division of labor takes place between the cells of the association: some cells take on the transport function for supply and disposal, others specialize in the utilization of nutrients, some cells have support functions or enable movement and still others are responsible for the coordination through information processing. The development of the characteristic properties of cells is called differentiation.
Identically differentiated cells are usually grouped together in larger groups; this cell structure is called tissue . The histology describes the structure and properties of the various tissues .
Individual evidence
- ↑ Erich Letterer: General pathology, foundations and problems: a textbook. Thieme, 1959. p. 324.