Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025
Definition
In the context of blood vessels within the cardiovascular system, the lumen is the inner open space or cavity through which blood flows. It varies in diameter in different types of vessels, affecting blood flow and pressure.
A thin layer of cells that lines the interior surface (lumen) of blood vessels, playing a key role in vascular functions such as controlling blood pressure and preventing clotting