Chondrocytes

What Are Chondrocytes?

Chondrocytes are the cells making up the cartilage. They are pivotal to synthesize cartilage matrix and sustain the extracellular matrix. It primarily comprises the proteoglycans and collagen. Chondrocytes are surrounded by the collagenous fibres and secrete substances causing the cartilage to acquire strength and flexibility.

Chondrocytes – Structure

It’s structure in the cartilage matrix is round or resembling a polygon, however, 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 ageing, mitotic figures are absent in normal adult AC (articular cartilage). The adult chondrocyte exhibits a variety in accordance to its position with its synthetic action, density and structure. If flattened, these cells are aligned parallelly to the surface in addition to the collagen fibres in the superficial zone (the highest cell density). In the innermost zones, the chondrocytes form the columns aligned 90 degrees to the surface of the cartilage along the collagen fibres. Chondrocytes appear more rounded and larger in the intermediate zone exhibiting a bottom distribution, where the fibres are oriented in a random pattern.

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

Chondrocytes – Location and Function

These structures are located in the intervertebral discs in any form of (AC) articular cartilage. Chondrocytes are cells producing and maintaining the cartilage matrix. They are vital in sustaining homeostasis in the AC joints rendering cushioning in the joint movements. Chondrocytes drift apart from each other by the cartilage matrix. These cells take charge of chondral repair. As they possess reconstructive capabilities, they are responsive to exterior trauma if there is damage to tissues.

In the fifth week of development, the initial cartilage comprises the mesenchyme which is crucial in activating the regions of chondral development. Additionally, it also condenses to make chondrification centres. Prechondrocytes are developed from mesenchymal cells that are the future chondroblasts. These structures in turn release extracellular matrix and collagenous fibrils. As a result, the elastic and collagenous fibres are accumulated in the intercellular matrix. The matrix hence formed conduces cartilaginous typecast.

Cartilages are of 3 main types –

  • Fibro-cartilage – part of vertebral disc and knees. Chondrocytes are present here in few numbers and hence it is the least flexible of all
  • Hyaline cartilage – found in joints, end of the ribs, nose and are second most flexible next to elastic cartilages.
  • Elastic cartilage – found in Eustachian tubes (ear). It contains the most number of chondrocytes, hence, they are the most flexible cartilages.

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.

Its perichondrium is the surface of the cartilage encircling the layer of dense irregular connective tissue. Perichondrium’s inner layer consists of chondroblasts and outer layer of fibroblasts that produce collagen.

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