Tunica externa

Tunica externa (also known as the adventitia) is the outermost layer of a blood vessel, surrounding the tunica media. It is mainly composed of collagen and, in arteries, is responsible for providing strength and flexibility.

Structure

The tunica externa is the outermost layer of a blood vessel, lying immediately beneath the epithelium. It is composed primarily of collagen fibers, which provide strength and flexibility to the vessel. In arteries, the tunica externa is thicker than in veins, reflecting the higher pressures within arteries.

The tunica externa also contains vasa vasorum, small blood vessels that supply the walls of larger blood vessels. These vessels are particularly important in supplying nutrients to the outer layers of large vessels, which cannot be adequately supplied by diffusion from the lumen.

Function

The primary function of the tunica externa is to provide structural support to the blood vessel, preventing it from collapsing or over-expanding in response to changes in blood pressure. The collagen fibers within the tunica externa are arranged in a way that allows the vessel to stretch and recoil, maintaining its shape and integrity even under high pressures.

In addition to providing structural support, the tunica externa also plays a role in the repair and remodeling of blood vessels. Following injury, cells within the tunica externa can proliferate and produce new collagen, helping to repair damage and maintain the integrity of the vessel.

Clinical significance

Abnormalities in the tunica externa can contribute to a variety of vascular diseases. For example, in atherosclerosis, the tunica externa can become thickened and fibrotic, contributing to the narrowing of the vessel lumen and the development of plaques. Similarly, in aneurysms, weakness in the tunica externa can lead to bulging and eventual rupture of the vessel.

See also

• Tunica intima
• Tunica media
• Blood vessel
• Atherosclerosis
• Aneurysm

References

Tunica externa Resources
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