Joint. Light micrograph showing a section through the tissues of a joint in the human body. The joint space is at centre. It is filled with synovial fluid, which lubricates and cushions the joint, preventing friction. Joints are covered in a form of hyaline cartilage called articular cartilage (purple). Cartilage is a type of connective tissue, which consists of an extracellular matrix and cells known as chondrocytes (dark purple). Chondrocytes, which produce and maintain the matrix, reside in holes known as lacunae. Beyond the cartilage is a layer of spongy bone (pink), consisting of trabeculae filled with bone marrow (white).