Harvard Heart Letter

Standing guard over blood vessel health

Damage to the endothelium sets the stage for cardiovascular disease.

The well-being of your heart and circulatory system depends on a layer of cells half the thickness of Scotch tape that stretches for thousands of miles. This layer, called the endothelium (en-doe-THEE-lee-um), was once thought to be little more than a barrier separating blood from the muscle, nerves, and connective tissue that make up arteries and veins. We now know that it is a dynamic regulator of blood vessel health. Damage to the endothelium, which often begins quietly in childhood, matures decades later as stiff or cholesterol-pocked blood vessels.

Anatomy of an artery

illustration of artery showing endothelial cells


The endothelium is a single layer of cells that lines all blood vessels. It provides a smooth, leak-free lining that keeps blood from seeping into the outer layers of blood vessel tissue. It also acts like an exquisitely sensitive organ that responds to physical and chemical signals. The endothelium regulates the following:

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