Levyepiteelin

Levyepiteelin refers to the squamous epithelium, a type of epithelial tissue composed of flat, plate-like cells that form a continuous cellular sheet. It exists in two main organizational forms: simple squamous epithelium, with a single cell layer, and stratified squamous epithelium, with multiple layers that provide greater protection.

Simple squamous epithelium lines areas where rapid diffusion or filtration occurs, such as the alveoli of the lungs, the lining of blood vessels (endothelium), and the glomerular capsule in the kidney. It also forms the mesothelium, the lining of serous membranes. Stratified squamous epithelium covers surfaces exposed to abrasion and chemical stress. The keratinized type forms the epidermis of the skin and provides waterproofing, while non-keratinized types line moist mucosal surfaces such as the oral cavity, esophagus, vagina, and anal canal.

Cellular structure: squamous cells are flattened and wide, with a flattened nucleus in the upper layers. In keratinized epithelium, surface cells die and accumulate keratin, creating a tough, water-resistant layer that protects underlying tissues.

Functions: the epithelium acts as a barrier to protect underlying tissues, participates in selective diffusion in simple forms, and reduces friction. Keratinized layers add durability and water resistance, while non-keratinized forms maintain moisture and flexibility in mucosal surfaces.

Clinical significance: neoplastic transformation of squamous epithelium gives rise to squamous cell carcinoma in organs such as the skin, lungs, and cervix. Screening and cytology detect abnormal squamous cells, and disruptions of the epithelial barrier can contribute to infections and impaired healing.

Development and origin: squamous epithelia arise from varied embryonic origins; epidermis derives from ectoderm, while endothelial and mesothelial linings derive from mesoderm, with other squamous regions reflecting analogous developmental patterns.