epitér

An epithel is a type of cell that lines the surfaces of the body, both externally and internally. These cells form protective coverings and barriers for organs, cavities, and all internal surfaces of the body. Epithelial tissue, composed of epithels, is one of the four primary types of animal tissue, along with connective tissue, muscle tissue, and nervous tissue. Epithels are characterized by being tightly packed together, forming continuous sheets. They also possess a free surface that is exposed to the outside of the body or to the lumen of an internal organ, and an attached surface that is anchored to underlying connective tissue by a basement membrane.

Epithels have various functions, including protection from mechanical injury, pathogens, and dehydration. They are also involved in absorption of nutrients, secretion of hormones and enzymes, and excretion of waste products. The specific function of an epithel depends on its location and its specific type. For instance, simple squamous epithels, which are single layers of flat cells, are ideal for diffusion and filtration in structures like the lungs and blood vessels. Stratified squamous epithels, composed of multiple layers of cells, provide robust protection in areas like the skin and the lining of the mouth. Other types include cuboidal epithels, which are cube-shaped and often involved in secretion and absorption, and columnar epithels, which are tall and rectangular, frequently found in the digestive tract where they aid in absorption and secretion. The shape and arrangement of epithels are crucial to their specialized roles within the body.