Endotheliu is a term that appears to be a misspelling or a non-standard term. It is highly likely that the intended term is "endothelium". The endothelium is a type of tissue that lines the interior surface of blood vessels and lymphatic vessels. It is a single layer of cells called endothelial cells. These cells are flattened and smooth, which helps to minimize friction as blood flows through the vessels. The endothelium plays a crucial role in regulating the passage of substances into and out of the bloodstream, acting as a selective barrier. It also participates in various physiological processes, including blood clotting, inflammation, and the formation of new blood vessels (angiogenesis). The health of the endothelium is vital for maintaining cardiovascular health, and dysfunction of this tissue is implicated in numerous diseases, such as atherosclerosis, hypertension, and diabetes. Maintaining a healthy endothelium involves factors like a balanced diet, regular exercise, and avoiding smoking.