Chondrocytes

The cells of the cartilage are known as chondrocytes. They are very important in the synthesis of cartilage matrix and in maintaining the extracellular matrix. It mainly comprises the proteoglycans and collagen. Chondrocytes are surrounded by the collagenous fibers and secrete substances causing the cartilage to acquire strength and flexibility.

1.0Introduction to Chondrocytes

• Skeletal cartilage is a supporting and articular skeletal tissue consisting of specialized cells (chondroblasts, chondrocytes, and chondroclasts) separated by pericellular and ECM composed of abundant ground substance rich in glycosaminoglycans (eg, chondroitin sulfate) and proteoglycans (eg, elastin fibers) that, depending on the cartilage type and the species, may mineralize or not (eg, invertebrates).

2.0Structure 

• Its structure in the cartilage matrix is round or resembling a polygon, however, the tissue boundaries are an exception where chondrocytes can be discoid or flattened at the articular surfaces of joints. Synthetically active cells are characterized by intracellular features.
• Despite the fact that senescence eventuates with aging, mitotic figures are absent in normal adult AC (articular cartilage).
• The adult chondrocyte varies in its synthetic activity, density, and structure with its location. These cells, flattened if viewed, are oriented parallel to the surface, as are the collagen fibers in the superficial zone, which contains the highest cell density. 
• In deeper zones, the chondrocytes form columns oriented 90 degrees to the surface of the cartilage along the collagen fibers.
• Here, the chondrocytes show an appearance of being more rounded and larger with a bottom distribution. In the intermediate zone, the fibre orientation is random.

• Because of their position, chondrocytes behave differently in different layers. 
• The zonal differences in synthetic attributes can remain in the primary chondrocyte cultures. 
• The primary cilia-which are sensory organelles in chondrocytes-account for spatial organization of cells in the developing growth plate. These primary cilia serve as a centre for hedgehog signaling, wingless type, and comprise mechanosensitive receptors.

3.0Differences between Chondroblasts and Chondrocytes

4.0Location and Function

• These structures are in the intervertebral discs in any shape of articular cartilage, AC. 
• Chondrocytes - these are the cells responsible for the production and maintenance of the cartilage matrix. 
• They play a very crucial role in maintaining homeostasis in the AC joints and providing cushioning to the joint movements. 
• The chondrocytes migrate away from one another due to the cartilage matrix. 
• These cells are responsible for chondral healing. Since these cells have reconstructive powers, they are sensitive to external injury if there is any injury to the tissues.
• During the fifth week of development, the first appearance of cartilage consists of mesenchyme, which has the role of activating the regions of chondral development. 
• It further condenses into chondrification centers. Mesenchymal cells develop into prechondrocytes, the future chondroblasts. These structures in turn release extracellular matrix and collagenous fibrils. Due to this, elastic and collagenous fibers are deposited in the intercellular matrix. 
• The matrix thus forms cartilaginous mold.
• The chondrocytes in growing cartilages are capable of division wherein the daughter cells formed stay around in clusters of 2-4 cells. 
• They are found sitting in lacunae which are matrices enclosing the compartments. While the older chondrocytes comprise fat droplets, the active cells are large in size and secretory in nature with basophilic cytoplasm since they comprise rough endoplasmic reticulum. 
• The surface of the cartilage is its perichondrium that encircles the layer of dense irregular connective tissue. 
• The inner layer of the Perichondrium has chondroblasts while the outer layer has fibroblasts that produce collagen. 
• Chondrocytes function in forming the cartilage matrix and maintaining the extracellular matrix. 
• They maintain a stable environment within the joints that creates insulation while they move. 
• Chondrocytes do this by synthesizing type II collagen, proteoglycan, and other proteins such as enzymes that degrade certain matrix components. 
• Chondrocytes, therefore, control the synthesis and breakdown of cartilage in the body.