While discussing epithelial and endothelial cells, it is not easy to distinguish them but researchers have come up with some distinct features. Endothelial cells cover the blood vessel inner surface, while epithelial cells cover outer surface of the internal organs and the body. The endothelial cells and epithelial cells are derived from the epithelium, but they have differences in position, structure, and function.
Difference in the Position
Endothelium, made up of endothelial cells, covers the inner surface of the blood vessels. The entire internal circulation of the circulatory system is covered by endothelial cells, that form the interface between blood and the vessel wall.
Epithelium, made of epithelial cells, not only covers the outer body surface but also the outer surface of all internal organs such, as the liver, stomach, intestine, lung, urethra, bladder and so on.
Differences in the Function
Endothelial cells can regulate blood flow in the blood vessels, by releasing NO (vasodilator) to promote blood circulation and blood pressure regulation. Endothelial cells can also secrete a variety of proteins involved in hemostatic function.
The epithelial cells in skin protect the subcutaneous tissue from damage, bacterial entry, harmful chemicals, and helps in limiting the loss of moisture. Epithelial cells of skin also secrete sweat for regulating body temperature. The epithelial cells, that cover pancreas, secrete digestion-promoting enzymes whereas small intestine surface epithelium absorbs nutrients from digestive food. To summarize, the main function of epithelial cells involves secretion, absorption, protection.
Differences in the Structure
Endothelial cells are monolayer structures with easy passage for water and oxygen molecules into the surrounding tissue. The endothelial tissue lacks packed endothelial morphology, which allows for the passage and diffusion.
Epithelial cells are tightly packed like bricks and have a variety of structures to protect from external environmental damage.
Endothelial cells are supported by vimentin filaments while epithelial cell structures are supported by keratin filaments.