The epithelial tissue is that tissue that is found on the underlying accumulations or agglomerations of the connective tissues; epithelial tissue is formed by one or several layers of cells that are joined together, covering each of the free surfaces of the living organism, forming the internal covering of cavities, body ducts, hollow organs, as well as mucous membranes and the glands. In these tissues, each of the existing cells are united with each other, thus forming a series of sheets characterized by an extracellular matrix that is limited, located below the epithelial cells, they are also not vascularized, so they are supported through broadcast; always under each epithelium there will be connective tissue and finally, this type of tissue is the only one that comes from the blastodermic layers. It should be noted that the term is composed of the suffix "epi" which means "on" and the root "telio" which means "cumulus". Its name originates from the fact that this type of tissue is located on accumulations of connective tissue.
There are certain types of epithelial cells that have tiny hairs, which are known as "cilia", whose function is to eliminate those foreign substances, an example of this are those that are produced in the respiratory tract. The epithelial tissue also constitutes the parenchyma of different organs, such as the liver. The epithelial tissues originate from the three germ layers that are: the ectoderm, which is where most of the skin emanates and the layer of the different natural cavities such as the mouth, the pores of the skin, the anus, the nostrils. The endoderm, the epithelium of almost the entire digestive tract, the liver, the respiratory tree, and the pancreas. The mesoderm, where everything that remains of the epithelium comes, in addition to the reproductive organs and the kidneys.
The three types of epithelial tissues are:
Lining epithelium: these form a lining on the external surfaces of the skin, digestive system or lungs; and internal to it, as in the case of blood vessels, pleurae and lymphatics; they are characterized by having a scarce extracellular matrix and the cells are very well joined together by binding complexes.
Glandular epithelium: it is constituted by a series of specialized cells in terms of secretion that can be grouped or isolated, establishing the unicellular or multicellular glands. This type of tissue is created thanks to the cells that constitute the glands that produce the excretion of fluids that have a different composition than blood plasma or other tissue fluids.
Sensory epithelium: this is specialized, in a general sense, to dress the different surfaces of the organism, almost always forming part of a complex apparatus that captures and processes signals that emanate from the environment where it develops.
