anatomy

Epithelial covering fabric

The coating epithelium covers the body surfaces, both external and internal. For this reason, the epithelial covering fabric has first of all the task of protecting; in some cases it also regulates the absorption of chemicals.

The coating epithelia are formed by tightly joined cells, with very little amorphous intercellular substance interposed. These cells are arranged to form continuous laminae : one of the faces of this lamina rests on the underlying basement membrane ; the other side is free, as it faces a free surface (for example blood, the internal lumen of an organ or the external environment in the case of the epidermis).

The basal membrane (or lamina) is a very thin layer of dense tissue anchored to the underlying connective tissue.

Functions of the coating epithelium:

  • Mechanical protection (from shocks, abrasions, pressures etc.);
  • Barrier function (against the loss of liquids or the penetration of germs);
  • Absorbent function (some substances allow it to pass through, to allow for example the absorption of nutrients, renal filtration or exchange of respiratory gases).

On the free side, the cells of some epithelial lining tissues have particular accessory structures, useful for the specific function of that fabric. It is the case, for example, of ciliated respiratory epithelia (with vibrating cilia) or of the intestinal mucosa (equipped with microvilli).

The epithelial lining tissues can be classified based on the number of cell layers that compose them and based on the shape of the cells themselves.

  • According to the cellular layers, three types of epithelial tissue can be distinguished:
    • Simple or monostratified : it consists of a single layer of cells
    • Pseudostratified : it is formed by a single layer of cells; however, their particular arrangement (offset in height) gives the impression that it is composed of multiple layers of cells .
    • Compounded or multilayered : it consists of multiple cell layers
  • based on the shape of the cells, three types of epithelial tissue can be distinguished:
    • Simple paving (flat or scaly): the cells that make it up are flattened , therefore more developed in width than in height (like tiles, similar to scales).
    • Prismatic : made up of cells of prismatic shape
      • Cubic or isoprismatic: the cells have the three diameters that are equivalent;
      • Cylindrical or batiprismatic or columnar: the cells develop in height;
    • Of Transition : constituted by cells that modify their shape in relation to the state of distension of the organ that they cover