Vaso vasorum

Vasa vasorum
Micrograph showing cystic medial degeneration. The tunica adventitia (also called tunica externia ;yellow at bottom of image) with vaso vasorum is also seen. Movat's stain.
Details
Identifiers
Latin	Vasa vasorum
Code	TH H3.09.02.0.06001
TA	A12.0.00.028
FMA	77433
Anatomical terminology []

The vasa vasorum (Latin, "the vessels of the vessels") is a network of small blood vessels that supply the walls of large blood vessels, such as elastic arteries (aorta) and large veins (venae cavae).

Studies conducted with 3-dimensional microcomputed tomography (3D Micro-CT) on pig and human arteries from different vascular beds have shown that there are three different types of vasa vasorum:

Depending on the type of vasa vasorum, it penetrates the vessel wall starting at the intimal layer (vasa vasorum interna) or the adventitial layer (vasa vasorum externa). Due to higher radial and circumferential pressures within the vessel wall layers closer to the main lumen of the artery, vasa vasorum externa cannot perfuse these regions of the vessel wall (occlusive pressure).

The structure of the vasa vasorum varies with the size, function and location of the vessels. Cells need to be within a few cell-widths of a capillary to stay alive. In the largest vessels, the vasa vasorum penetrates the outer (tunica adventitia) layer and middle (tunica media) layer almost to the inner (tunica intima) layer. In smaller vessels it penetrates only the outer layer. In the smallest vessels, the vessels' own circulation nourishes the walls directly and they have no vasa vasorum at all.

Vasa vasorum are more frequent in veins than arteries. Some authorities hypothesize that the vasa vasorum would be more abundant in large veins, as partial oxygen pressure and osmotic pressure is lower in veins. This would lead to more vasa vasorum needed to supply the vessels sufficiently. The converse argument is that generally artery walls are thicker and more muscular than veins as the blood passing through is of a higher pressure. This means that it would take longer for any oxygen to diffuse through to the cells in the tunica adventitia and the tunica media, causing them to need a more extensive vasa vasorum.

A later method of scanning is optical coherence tomography that also gives 3D imaging.

The vasa vasorum are found in large vein and arteries such as the aorta and its branches. These small vessels serve to provide blood supply and nourishment for tunica adventitia and outer parts of tunica media of large vessels.