The epithelium is the outer layer that protects the tissues from the external environment. Therefore, it is present in the skin, gastrointestinal tract, lungs, etc. Initially, endothelium, present in blood vessels and lymphatic vessels, was thought to be a type of epithelial layer, but numerous studies marked a clear distinction between both cells.
- All three germ layers form epithelial cells, whereas endothelial cells originate from mesoderm.
- Epithelial cells always form a continuous barrier over the tissue, while the endothelium can vary from a continuous to a discontinuous surface, depending on the underlying tissue.
- Epithelial cells are involved in functions such as protection of the tissue, transport of nutrients across tissue, and secretion of hormones. Endothelial cells regulate the traffic of cells and other biomolecules between vessels and tissue, control vasodilation, prevent coagulation, and mediate inflammation.
- Epithelial cells are mostly applied in cancer research, wound healing, drug transport, toxicity studies, etc. After the exploitation of endothelial structure in tumour therapy, endothelial cells gained more attention. Presently, they are used to study inflammation, hypertension, tissue-specific changes, vasculogenesis, angiogenesis, and cardiovascular diseases.