epithelets

Epithels are a type of cell that form epithelial tissue. This tissue is found on all free surfaces of the body, both internal and external. Epithelial tissues cover the body's outer surface, line body cavities and hollow organs, and form glands. Their primary functions include protection, secretion, absorption, excretion, filtration, diffusion, and sensory reception.

Epithelial cells are characterized by several key features. They have a high rate of cell division, allowing for regeneration and repair. They are typically arranged in continuous sheets, with very little extracellular space between cells. Epithelial cells are polarized, meaning they have distinct apical (top) and basal (bottom) surfaces. The basal surface is attached to a basement membrane, a thin layer of connective tissue. Epithelial tissues are classified based on the number of cell layers and the shape of the cells. Simple epithelia consist of a single layer of cells, while stratified epithelia have multiple layers. Cell shapes can be squamous (flat), cuboidal (cube-shaped), or columnar (tall and rectangular).

The specific type and arrangement of epithelial cells are adapted to their particular function. For example, simple squamous epithelium in the lungs facilitates diffusion of gases, while stratified squamous epithelium in the skin provides a protective barrier against abrasion. Glands, which are specialized epithelial structures that secrete substances, can be unicellular or multicellular and can be exocrine (secreting onto a surface) or endocrine (secreting into the bloodstream).