Specialised connective tissue
The special connective tissue cartilage, bone and blood – each have unique cells and extracellular matrices that allow specialized functions.
• Cartilage is a soft skeletal tissue. It is not rigid like bone.
• It is found more abundantly in vertebrate embryo because most of the bones forming skeleton of the adult are cartilaginous in the early stage.
Structure of cartilage
• A typical cartilage consists of cartilage cells and ground substance (matrix).
(i) Cartilage cells or chondrocytes : They are present in a fluid-filled space, called lacunae within the cartilage ground substance. Young cartilage cells (chondroblasts) are small and flattened whereas mature cartilage cells (chrondrocytes) are large and rounded.
(ii) Ground substance (matrix) : It essentially consists of water, proteoglycans, some lipid, collagen, non-collagenous protein and fibres. The core protein is aggrecan. Carbohydrates are glucosaminoglycans (GAG) including chondroitin sulphate, keratin sulphate and hyaluronic acid.
Chondrocytes remain alive, even though there are no blood vessels in the cartilage matrix, because they receive oxygen and nutrients by diffusion through ground substance from surrounding blood vessels. This diffusion can only occur because cartilage matrix is not calcified.
Types of cartilage
• The cartilage is divided into three types as shown in the table below