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Chondrocytes

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

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.

Structure of chondrocytes

  • 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

Chondroblast

Chondrocytes

Chondroblasts are the developmental cartilage    cells that are involved in the development of the cartilage tissue.

Chondrocytes are mature cartilage cells that function to maintain the cartilage structure.

These cells actively produce the component of the ECM.

These cells secrete ECM and are embedded in it.

These cells originate from a type of mesenchymal progenitor cell.

These cells originate from the chondroblasts.

Immature cartilaginous cells.

Mature cartilaginous cells.

Appositional growth of the cartilage by chondroblasts.

Interstitial growth of the cartilage by chondrocytes.

The main function is to produce chondrocytes and components of the ECM.

Primarily, to maintain the structure of the cartilage and ECM.

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.

Frequently Asked Questions

Chondrocytes are specialized cells of cartilage that synthesize the extracellular matrix, which is mainly composed of collagen and proteoglycans.

The primary functions of chondrocytes include the production and maintenance of the cartilage matrix, which provides the form, support, and elasticity of tissues such as joints, intervertebral disks, and ears.

Chondrocytes are found in hyaline cartilage, which is the one forming the joints, elastic cartilage, that can be found in the ear and epiglottis, and fibrocartilage, utilized between intervertebral disks.

Chondrocytes maintain the health of cartilage through the synthesis and regulation of balanced extracellular matrix components including collagen-proteoglycans, by responding to mechanical stimuli and biochemical signals.

Some factors may include aging, mechanical stress, inflammation, and genetic mutations that can affect chondrocyte function and lead to cartilage degeneration or diseases such as osteoarthritis.

In osteoarthritis, chondrocytes are less effective at maintaining the cartilage matrix, leading to cartilage breakdown, loss of joint function, and pain.

While the pathophysiology of cartilage does permit some natural repair of damaged cartilage, not many of these reparative processes happen naturally. Investigations into tissue engineering and regenerative medicine focus on approaches aimed at enhancing the function of chondrocytes to effect cartilage repair.

Chondrocytes undergo the process of chondrogenesis during the development of cartilage, which includes proliferation, differentiation, and arrangement of cells to form the structure of cartilage in growing bones and tissues.

Investigators study the biology of chondrocytes by in vitro culture of chondrocytes, animal models, and advanced gene editing, imaging, and biomechanical testing techniques to develop treatments for cartilage-related diseases.

Current putative therapies targeting chondrocytes include gene therapy, stem cell therapy, and growth factor/cytokine therapies aimed at enhancing chondrocyte activity to improve cartilage repair in conditions such as osteoarthritis.

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