Chondrocytes

What Are Chondrocytes?

Chondrocytes are cells that produce and maintain cartilage, which is a type of connective tissue that cushions and supports other tissues and organs in the body.

Chondrocytes are the cells that make up cartilage and are essential for the synthesis of the cartilage matrix and maintenance of the extracellular matrix. This matrix mainly consists of proteoglycans and collagen, and the chondrocytes are surrounded by collagenous fibres. These cells also secrete substances that give the cartilage strength and flexibility.

Chondrocytes: Structure

The structure of the cartilage matrix is typically round or polygonal in shape, however, tissue boundaries are an exception as chondrocytes can be discoid or flattened at the joint surfaces. Synthetically active cells are characterized by their intracellular features.

Despite ageing leading to senescence, mitotic figures are not present in normal adult Articular Cartilage (AC). Adult chondrocytes vary in their action, density, and structure depending on their position. In the superficial zone (the highest cell density), these cells are flattened and aligned parallel to the surface in addition to the collagen fibres. In the innermost zones, the chondrocytes form columns that are perpendicular to the surface of the cartilage and aligned with the collagen fibres. Chondrocytes appear more rounded and larger in the intermediate zone, where the fibres are arranged in a random pattern and the cells are distributed at the bottom.

Chondrocytes exhibit varied behavior depending on their location. The primary chondrocyte cultures can maintain the zonal differences in their synthetic properties. Primary cilia are vital for the spatial organization of cells in the growing growth plate, and are sensory organelles in chondrocytes. These primary cilia serve as the hub for hedgehog signalling, wingless type and contain mechanosensitive receptors.

Chondrocytes: Location and Function
Chondrocytes are the main cell type found in cartilage and are located in the perichondrium, the layer of tissue surrounding cartilage. They are responsible for the production and maintenance of the extracellular matrix, which provides support and flexibility to the cartilage.

The intervertebral discs contain any type of articular cartilage (AC). The chondrocytes within the AC are responsible for producing and maintaining the cartilage matrix. This matrix is vital in providing cushioning and sustaining homeostasis in the AC joints. When the matrix is damaged, the chondrocytes can drift apart and take charge of chondral repair due to their reconstructive capabilities.

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 is a part of the vertebral disc and knees, and contains few chondrocytes, making it the least flexible of all.

Hyaline cartilage is found in joints, the end of the ribs, the nose, and is the second most flexible type of cartilage after elastic cartilage.

Elastic cartilage is found in Eustachian tubes (ear) and contains the most number of chondrocytes, making it the most flexible of all 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.

The Perichondrium is a surface of cartilage that is encircled by a layer of dense irregular connective tissue. It has an inner layer made up of chondroblasts and an outer layer of fibroblasts that produce collagen.

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