epitéliumán

Epithelial tissue, often referred to as epithelium, forms a continuous sheet of cells that covers the external surfaces of the body, lines internal cavities and passageways, and forms glands. Its primary functions include protection, secretion, absorption, excretion, filtration, diffusion, and sensory reception. Epithelial cells are tightly packed together with minimal extracellular material, forming a barrier. They are anchored to underlying connective tissue by a basement membrane.

Epithelium is classified based on two main criteria: the number of cell layers and the shape of the cells. In terms of layers, it can be simple (a single layer of cells) or stratified (multiple layers of cells). Simple epithelium is typically found where absorption, secretion, and filtration occur, while stratified epithelium provides protection in areas subject to abrasion.

Cell shapes are described as squamous (flat and thin), cuboidal (cube-shaped), or columnar (taller than they are wide). Simple squamous epithelium is ideal for diffusion and filtration, found in alveoli of the lungs and lining of blood vessels. Simple cuboidal epithelium is involved in secretion and absorption, lining kidney tubules and ducts of glands. Simple columnar epithelium, often with microvilli or cilia, aids in absorption and secretion, lining the digestive tract. Stratified squamous epithelium, the most common stratified type, protects underlying tissues, found in the skin and lining of the mouth. Other types include pseudostratified columnar and transitional epithelium, which has the ability to stretch.