The tunica intima is the innermost layer of blood vessel walls, consisting of a single layer of endothelial cells supported by a thin layer of connective tissue. This layer plays a crucial role in maintaining vascular homeostasis by providing a smooth surface for blood flow, reducing friction, and regulating vascular tone through the release of vasoactive substances. Endothelial cells also act as a barrier, controlling the passage of materials and cells between the bloodstream and surrounding tissues.
