Epiteltypen

Epiteltypen, also known as epithelial tissue types, are classifications of the cells that form the outer surfaces of the body, the lining of internal organs and cavities, and glandular tissue. These tissues are characterized by cells that are tightly packed together, forming continuous sheets. The primary functions of epithelia include protection, secretion, absorption, excretion, filtration, diffusion, and sensory reception. Epithelia are broadly categorized based on two main criteria: the number of cell layers and the shape of the cells.

Based on the number of cell layers, epithelia are classified as simple or stratified. Simple epithelia consist of a single layer of cells, which are typically found where absorption, secretion, and filtration occur. Examples include simple squamous epithelium in blood vessels and air sacs of the lungs, simple cuboidal epithelium in kidney tubules and ducts of glands, and simple columnar epithelium lining the digestive tract. Stratified epithelia are composed of two or more layers of cells, providing protection in areas subjected to abrasion. The most common type is stratified squamous epithelium, found in the skin and lining of the mouth.

Based on cell shape, epithelia are described as squamous, cuboidal, or columnar. Squamous cells are flattened and scale-like. Cuboidal cells are cube-shaped, with height and width approximately equal. Columnar cells are taller than they are wide. Pseudostratified columnar epithelium, although appearing to have multiple layers due to differing cell heights, is actually a simple epithelium because all cells rest on the basement membrane. Transitional epithelium is a specialized stratified epithelium found in the urinary bladder, capable of stretching. Glandular epithelia are specialized for secretion and form glands, which can be unicellular or multicellular.