It is made up of one layer of endothelial cells (and macrophages in areas of disturbed blood flow),[1][2] and is supported by an internal elastic lamina.

It is a fine, transparent, colorless structure which is highly elastic, and, after death, is commonly corrugated into longitudinal wrinkles.

However, endothelium has been shown to release local chemicals called endothelins which are powerful vasoconstrictors.

[4] Endothelins help to regulate capillary exchange and alter blood flow by their constriction of the smooth muscle in the walls.

[5] This article incorporates text in the public domain from page 498 of the 20th edition of Gray's Anatomy (1918)