The synovium

Synovium is the soft tissue lining the spaces of diarthrodial joints, tendon sheaths, and bursae. The term includes both the continuous surface layer of cells (intima) and the underlying tissue (subintima). The intima is com-posed of specialized macrophages and fibroblasts, and the subintima con-tains blood and lymphatic vessels, a cellular content of both resident fibroblasts and infiltrating cells in a collagenous extracellular matrix. Between the intimal surfaces is a small amount of fluid, usually rich in hyaluronan (hyaluronic acid). Together, this structure provides a nonadher-ent surface between tissue elements. Unlike serosal surfaces, which also have nonadherent properties, synovium is derived from ectoderm and does not contain a basal lamina.