epiteelilajit

Epiteelilajit, or epithelial tissue types, are classifications of the cells that line the surfaces of organs and form glands. These tissues are distinguished by their shape and the number of cell layers present. The primary shapes are squamous (flat), cuboidal (cube-shaped), and columnar (taller than they are wide). The number of layers can be simple (one layer) or stratified (multiple layers).

Simple squamous epithelium is found where diffusion and filtration are important, such as in the alveoli of the lungs and the lining of blood vessels. Simple cuboidal epithelium is common in glands and kidney tubules, involved in secretion and absorption. Simple columnar epithelium lines the digestive tract, aiding in absorption and secretion, and may feature microvilli or cilia.

Stratified squamous epithelium provides protection against abrasion and is found in the skin and the lining of the mouth. Stratified cuboidal and stratified columnar epithelia are less common, typically found in ducts of larger glands, where they also serve protective roles. A special type, pseudostratified columnar epithelium, appears layered but all cells touch the basement membrane, often found in the respiratory tract and characterized by cilia. Transitional epithelium lines organs that stretch, like the bladder, allowing for distension.