Areolar connective tissue, like connective tissues in general, holds us together. Like all connective tissues, it contains a lot of nonliving material — the extracellular matrix. In this case the matrix is loose and unspecialized, with a large amount of interstitial fluid, making it an ideal “filler” between many structures in the body. In particular, it is found on the back side of almost every epithelium in the body, including the lining of blood vessels. As a result, every molecule that crosses between the blood and surrounding tissues, has to diffuse across areolar connective tissue — the “middleman” of exchange.
Epithelia line not just the blood vessels, but every other surface and cavity of the body. This means they can function not only as an exchange surface, but also a barrier to microorganisms. Here again, areolar connective tissue plays a vital role — as the “second line of defense”, harboring immune cells that attack any invaders that breach our defenses.
I’ve already paid homage to some of our other connective tissues. The dense connective tissues are distinguished by large amounts of collagen, making them strong, though flexible. Bone tissue contains a rigid mineral component making it an ideal structural support. Areolar connective tissue, by comparison, is weak and shapeless. But this unpretentious mass of matrix and cells is arguably even more important for our survival.