Cellskikt

Cellskikt, or cell layer, refers to a sheet-like arrangement of cells that covers surfaces, lines cavities, or forms glands. In histology the term is often used for epithelial tissue, where cells are tightly bound to one another and rest on a basement membrane. The cellskikt serves as a selective barrier between compartments and provides interfaces for protection, absorption, secretion, and diffusion.

Cells in a cellskikt are held together by several types of cell junctions, including tight junctions, adherens junctions, desmosomes, and gap junctions. The layer exhibits apical-basal polarity, with the apical surface facing the lumen or external environment and the basal surface anchored to the basement membrane. Epithelial cellskikt arise from the germ layers during development and can vary in thickness and shape.

There are different organizational types of cellskikt. A simple cellskikt consists of a single cell layer, and its cells can be squamous, cuboidal, or columnar. A stratified cellskikt has two or more cell layers, commonly protecting areas subject to abrasion such as the skin or esophagus. A pseudo-stratified columnar cellskikt appears multi-layered but all cells contact the basement membrane. Transitional epithelium, found in the urinary tract, is a specialized form capable of stretching.

Functions of a cellskikt include protection against mechanical and chemical injury, selective absorption (as in the intestinal lining), secretion (glands), and filtration (as in kidney tubules). Pathologically, damage or transformation of epithelial cellskikt can lead to disorders such as infections, barrier breakdown, or carcinomas arising from epithelial cells.