(en‵dŏ-thē'lē-ŭm )

[endo- + Gr. thēlē, nipple, teat]

A form of squamous epithelium-like tissue consisting of flat cells that line the blood and lymphatic vessels, the heart, and various other body cavities. Endothelium differs from epithelium in that the former is derived from mesoderm while the later is derived from ectoderm or endoderm. Taken together, the endothelium throughout the body has a surface area more than twice that of the skin. Endothelial cells are metabolically active and produce a number of compounds that affect the vascular lumen and platelets. Included are endothelium-derived relaxing factor (EDRF), prostacyclin, endothelium-derived contracting factors 1 and 2 (EDCF1, EDCF2), endothelium-derived hyperpolarizing factor (EDHF), and thrombomodulin.

SEE: intima.

endothelial,

(en‵dŏ-thē'lē-ăl )