Humans, like other animals, are made up of four basic tissue groups: the epithelial, the connective, O muscular it's the nervous. O epithelial tissue, also called epithelium, it is made up of juxtaposed cells with little extracellular substance.
Epithelial tissues primarily have two functions: coat and secrete. the epithelia of coating they form a covering over the surfaces and cavities of the body that prevents excessive water loss and the entry of pathogenic organisms. In addition, they also allow the exchange of substances and the absorption of nutrients, among many other functions. The epithelial tissues with the function of secretion are called glandular and play important roles in our body, such as temperature control and growth and development control.
The cells of the lining epithelial tissues have different shapes and characteristics, and these factors are used for their classification. Among the main criteria used to classify epithelia, the number of layers and cell shapes stand out.
According to the number of layers, the epithelia can be classified into:
→ Simple: They have only one layer of cells.
→ Stratified: They have more than one layer of cells.
→ Pseudostratified: Tissue formed only by a layer of cells, however, the varied position of the nuclei promotes the false sensation that it has several layers. Although all cells are supported on the basal lamina, they differ in height and, therefore, not all reach the tissue surface.
Pseudostratified tissue has only one layer of cells
Taking into account the shape of the cells, the epithelium can be classified into:
→ Floor: Flat-shaped cells that often resemble tiles. Pavement epithelia, which can be simple or stratified, can be found lining blood vessels and forming the epidermis, for example (Read more about the skin);
→ Cubic: Cubic-shaped cells. Cubic epithelia can be simple or stratified and can be seen in the ovary and ovarian follicles, for example.
→ Prismatic, columnar or cylindrical: Elongated and rectangular cells. Prismatic epithelia can be simple or stratified and can be found lining the trachea and nasal cavity, for example.
→ Transition: A type of stratified tissue with superficial cells of a globose shape that change according to the degree of tissue distension. This type of epithelium is found in the bladder.
The tissue above is stratified — it has more than one layer of cells — and paved
The type of epithelium found in each organ is directly related to the function of that particular structure. Simple squamous epithelia, for example, are found in places where the exchange of substances must easily take place. On the other hand, pavement stratified, for example, make it difficult to exchange substances and are more related to protection.
Learn more about fabrics in the section Histology!
By Ma. Vanessa dos Santos
Source: Brazil School - https://brasilescola.uol.com.br/biologia/classificacao-dos-tecidos-epiteliais.htm
