Epiteelirakud

Epiteelirakud, commonly known as epithelial cells, form a fundamental tissue type in the body. They are densely packed cells that cover the surfaces of organs, line body cavities, and form glands. Their primary functions include protection, secretion, absorption, excretion, filtration, diffusion, and sensory reception. Epithelial tissues are characterized by their close apposition to each other and the presence of specialized cell junctions that provide structural support and regulate the passage of substances.

These cells are avascular, meaning they do not have their own blood supply, and they receive nutrients by diffusion from underlying connective tissues. Epithelial tissues are classified based on their shape and the number of cell layers. Cell shapes can be squamous (flat), cuboidal (cube-shaped), or columnar (tall and rectangular). The number of layers can be simple (a single layer) or stratified (multiple layers). Pseudostratified epithelium, which appears to have multiple layers but all cells touch the basement membrane, is another classification.

The apical surface of epithelial cells faces a lumen or the external environment, while the basal surface is attached to a basement membrane, a thin layer of extracellular matrix. Depending on their location and function, epithelial cells can exhibit specialized structures such as cilia, which help move substances along the surface, or microvilli, which increase surface area for absorption. The continuous regeneration of epithelial cells is crucial for maintaining tissue integrity and function.