intimal

Intimal is an adjective relating to the tunica intima, the innermost lining of blood vessels and heart chambers. In arteries, veins, and capillaries, the intima forms a thin layer between the lumen and the media. It is primarily composed of endothelial cells that rest on a basement membrane, with a subendothelial connective tissue layer; an internal elastic lamina is present in many arteries and marks the boundary with the media.

Functions of the intima include providing a semipermeable barrier and an active role in vascular homeostasis. The endothelium produces substances such as nitric oxide and endothelin that regulate vessel diameter, platelet activity, and coagulation. The intima helps regulate immune cell trafficking and maintains a largely non-thrombogenic surface under normal conditions.

Clinical relevance: Changes in the intima underlie many vascular diseases. Intimal thickening or hyperplasia can occur after vascular injury or surgery and may contribute to luminal narrowing. Atherosclerosis involves lipid deposition, inflammatory cell infiltration, and smooth muscle proliferation within the intima, creating plaques that can impede blood flow. In acute dissections, a tear can extend into or along the intimal layer, producing an intimal flap that partitions the lumen. In venous valves and certain congenital conditions, components of the intimal layer contribute to disease processes as well.

Etymology and usage: The term intimal is used to describe anything pertaining to the tunica intima, as opposed to the adventitia or media. It is commonly used in angiology and pathology.