endothelium (n.), endothelial (adj.)

https://doi.org/10.1351/goldbook.10661
Layer of flat cells that line the blood vessels, lymphatic vessels, and the chambers of the heart.
Source:
PAC, 2016, 88, 713. (Glossary of terms used in developmental and reproductive toxicology (IUPAC Recommendations 2016)) on page 749 [Terms] [Paper]