The term vasa vasorum translates from Latin as “the vessels of the vessels.” This describes a network of small blood vessels that supply blood to the walls of larger arteries and veins, such as the aorta. Large blood vessels have walls too thick to receive nourishment directly from the blood flowing through their main channel, or lumen, making this network necessary for the vessel walls to remain healthy.
Anatomy and Function
The walls of large blood vessels are composed of three layers: the inner tunica intima, the middle tunica media, and the outer tunica adventitia. The vasa vasorum are found within the tunica adventitia and the outer portion of the tunica media. Cells in the inner layers of the vessel wall can obtain nutrients through diffusion from the main lumen, but this is only effective over a short distance. The vasa vasorum penetrate the outer layers, forming a micro-circulatory system that delivers substances and removes waste products, maintaining the structural integrity of the vessel.
Differences in Arteries and Veins
The development and density of the vasa vasorum differ between large arteries and veins. This difference is due to the oxygen content of the blood they transport. Large veins, which carry deoxygenated blood, possess a more extensive network of vasa vasorum compared to arteries. The low-oxygen environment within veins means diffusion from the lumen provides little nourishment, requiring a robust external blood supply.
In contrast, arteries carry oxygen-rich blood. The high concentration of oxygen in arterial blood allows for more effective diffusion into the vessel wall, nourishing a deeper portion of the tunica media. Pressure dynamics also play a role; the high pressure within arteries restricts these small vessels to the outer layers, while the lower pressure in veins permits the vasa vasorum to perfuse more of the vessel wall.
Clinical Significance
The health of the vasa vasorum is directly linked to the health of the large blood vessels they supply. In atherosclerosis, the growth of atherosclerotic plaques is accompanied by the proliferation of new vasa vasorum, a process called neovascularization. These new vessels are often immature and leaky, which can lead to hemorrhage inside the plaque. This internal bleeding can destabilize the plaque, increasing the risk of rupture, which can cause a heart attack or stroke.
Dysfunction of the vasa vasorum can also compromise the aorta’s structural integrity. An insufficient blood supply, inflammation, or destruction of these vessels can weaken the aortic wall, contributing to an aortic aneurysm. A tear within the vasa vasorum can also initiate an aortic dissection, where blood flows between the layers of the aortic wall.