Interstitium

In anatomy, the interstitium is a contiguous fluid-filled space existing between a structural barrier, such as a cell membrane or the skin, and internal structures, such as organs, including muscles and the circulatory system. Fluid in this space – the interstitial fluid – is composed of solutes and water draining into the lymphatic system.

The interstitial compartment is composed of connective tissues comprising an extracellular matrix, which is situated outside the blood, lymphatic vessels, and the parenchyma of organs. The interstitium has a role in regulating solute concentration, protein transport, and hydrostatic pressure, which may affect human pathology and physiological responses, such as edema, inflammation, and shock.

Structure

The non-fluid parts of the interstitium are predominantly collagen types I, III, and V; elastin; and glycosaminoglycans, such as hyaluronan and proteoglycans, that are cross-linked to form a honeycomb-like reticulum. Collagen bundles of the extracellular matrix form scaffolding with a high tensile strength. Interstitial cells (e.g., fibroblasts, dendritic cells, adipocytes, interstitial cells of Cajal and inflammatory cells, such as macrophages and mast cells), serve a variety of structural and immune functions. Fibroblasts synthesize the production of structural molecules as well as enzymes that break down polymeric molecules. Such structural components exist both for the general interstitium of the body, and within individual organs, such as the myocardial interstitium of the heart, the renal interstitium of the kidneys, and the pulmonary interstitium of the lungs.

The interstitium in the submucosae of visceral organs, the dermis, superficial fascia, and perivascular adventitia are fluid-filled spaces supported by a collagen bundle lattice.