endothelium

n. layer of cells that lines the serous cavities the heart and the lymph/blood vessels (Biology)

This article is about the lining of blood vessels. For the endothelium of the cornea, see corneal endotheliumThe endothelium is the thin layer of cells that line the interior surface of blood vessels, forming an interface between circulating blood in the lumen and the rest of the vessel wall. Endothelial cells line the entire circulatory system, from the heart to the smallest capillary. These cells reduce friction of the flow of blood allowing the fluid to be pumped further.
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Endothelium /en·do·the·li·um/ pl. endothe´lia the layer of epithelial cells that lines the cavities of the heart, the serous cavities, and the [more]Endothelium - Community and Resources

Noun
1. an epithelium of mesoblastic origin; a thin layer of flattened cells that lines the inside of some body cavities
(hypernym) epithelium, epithelial tissue

n. endothelium, layer of cells that lines the serous cavities the heart and the lymph/blood vessels (Biology)