Epiteliaalista

Epiteliaalista refers to epithelial tissue, a fundamental type of animal tissue. Epithelial tissue covers the surfaces of the body, both externally and internally, and lines body cavities and organs. Its primary functions include protection, secretion, absorption, excretion, filtration, diffusion, and sensory reception.

Epithelial cells are tightly packed together, forming continuous sheets. They are characterized by having a free surface (apical surface) that is exposed to the body's exterior or to the lumen of an internal organ, and an attached basal surface that rests on an underlying basement membrane. This basement membrane separates the epithelium from the connective tissue.

Epithelial tissues are classified based on their cell shape and the number of cell layers. Cell shapes include squamous (flat), cuboidal (cube-shaped), and columnar (taller than they are wide). The number of layers can be simple (a single layer of cells) or stratified (multiple layers of cells). Pseudostratified epithelium appears to have multiple layers but actually consists of a single layer where cell nuclei are at different levels. Transitional epithelium is a specialized type found in organs that stretch, like the bladder, where cells can change shape.

The specific type and arrangement of epithelial cells are adapted to their particular function. For instance, simple squamous epithelium, being very thin, is ideal for diffusion and filtration, found in the alveoli of the lungs and the lining of blood vessels. Simple cuboidal and columnar epithelia are often involved in secretion and absorption, lining glands, the digestive tract, and kidney tubules. Stratified epithelia provide protection due to their multiple layers, such as the epidermis of the skin.