👉 An endothelial cell, also known as an endothelium, is a type of epithelial cell that lines blood vessels and plays a crucial role in blood vessel function. These cells are composed of specialized proteins such as integrins, which allow them to interact with other cells and tissues. The endothelial cells provide a barrier against the movement of substances such as cholesterol, blood clots, and bacteria, allowing for efficient transport of nutrients, oxygen, and waste products from the blood into the surrounding