Epithelial Tissue
The epithelium is a sheet of aggregated cells of similar type that covers body surfaces, lines hollow organs or modified to form glands or neuroepithelium.
General Features of Epithelium
- It may originate from all three embryonic germ layers (ectoderm, mesoderm and endoderm).
- It is composed of high number of closely applied cells with very little intercellular substances.
- It is separated from the underlying connective tissue by a basement membrane.
- It is avascular, blood and lymph vessels do not penetrate the basement membrane. Thus, it receives its nutritional support by diffusion.
- The epithelial cells have high capacity for regeneration.
The epithelium can change from one form to another in a process called metaplasia.
- It performs many functions such as protection, secretion, excretion, absorption and sensory reception.