Tunica intima

Tunica intima

The tunica intima (or intima) is the innermost layer of an artery or vein. It is composed of a thin layer of endothelial cells that line the lumen of the vessel, supported by a subendothelial layer of connective tissue and an internal elastic lamina in arteries.

Diagram of artery wall structure, showing the tunica intima.

Structure

The tunica intima is primarily made up of a single layer of endothelial cells that are in direct contact with the blood flow. Beneath the endothelial layer, there is a thin layer of connective tissue, which may contain a few smooth muscle cells. In arteries, the intima is separated from the tunica media by the internal elastic lamina, a layer of elastic fibers that provides elasticity and flexibility to the vessel wall.

Cross-section of an artery, showing the tunica intima.

Function

The primary function of the tunica intima is to provide a smooth lining for the lumen of the vessel, minimizing resistance to blood flow. The endothelial cells play a crucial role in vascular biology, including the regulation of blood flow, blood pressure, and hemostasis. They also serve as a barrier to the passage of materials and cells into and out of the bloodstream.

Clinical significance

The tunica intima is often involved in the development of atherosclerosis, a condition characterized by the buildup of plaque within the arterial walls. This can lead to cardiovascular diseases such as coronary artery disease and stroke. The process begins with damage to the endothelial cells, followed by the accumulation of lipids, inflammatory cells, and fibrous elements, forming atherosclerotic plaques.

Atherosclerotic plaque in the tunica intima.

Comparison with veins

In veins, the tunica intima is similar in structure to that in arteries but is generally thinner and lacks the internal elastic lamina. Veins also have valves, which are folds of the intima that prevent the backflow of blood.

Diagram of a vein, showing the tunica intima and valves.

Related pages

• Endothelium
• Atherosclerosis
• Artery
• Vein

References

• Ross, R., & Glomset, J. A. (1976). The pathogenesis of atherosclerosis (first of two parts). New England Journal of Medicine, 295(7), 369-377.
• Libby, P. (2002). Inflammation in atherosclerosis. Nature, 420(6917), 868-874.

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