epithelsejteket

Epithelsejtek, also known as epithelial cells, are a type of cell that forms the epithelial tissue. Epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue, and nervous tissue. Epithelial cells cover the surfaces of the body, both internally and externally. They line organs, cavities, and passages, and also form glands.

The primary functions of epithelial cells are protection, secretion, absorption, excretion, filtration, diffusion, and sensory reception. Their specific role depends on their location within the body. For instance, epithelial cells in the skin provide a protective barrier against the environment, while those lining the digestive tract are specialized for absorption of nutrients.

Epithelial cells are characterized by their close packing, forming continuous sheets. They have distinct apical (free) surfaces that face the external environment or the lumen of an internal cavity, and basal surfaces that are attached to underlying connective tissue. This polarity is crucial for their function. They are also typically avascular, meaning they do not have their own blood supply, and receive nutrients by diffusion from the underlying connective tissue. Epithelial cells can be classified based on their shape, such as squamous (flat), cuboidal (cube-shaped), and columnar (tall and rectangular), and also by the number of layers they form, such as simple (one layer) or stratified (multiple layers).