Epitélio

Epitélio is a type of animal tissue that covers body surfaces, lines body cavities, and forms glands. It is characterized by cells that are tightly packed together with very little extracellular matrix. These cells are typically arranged in one or more layers and rest on a basement membrane, which separates the epithelium from the underlying connective tissue.

Epithelial tissues perform a variety of functions, including protection, absorption, secretion, excretion, filtration, diffusion, and sensory reception. The specific function of an epithelial tissue is often related to its structure. For example, simple squamous epithelium, which is a single layer of flattened cells, is ideal for diffusion and filtration, found in the lungs and blood vessels. Stratified squamous epithelium, composed of multiple layers of cells, provides a barrier against abrasion and is found in the skin and lining of the mouth.

Epithelial cells can also be specialized for secretion, forming glandular epithelium. These glands can be exocrine, releasing their secretions onto an epithelial surface (e.g., sweat glands, salivary glands), or endocrine, secreting hormones directly into the bloodstream (e.g., thyroid gland, adrenal gland). The shape of the epithelial cells can be squamous (flat), cuboidal (cube-shaped), or columnar (tall and rectangular). This classification, combined with the number of cell layers, defines the major types of epithelial tissues.