Chondrocyte is the name given to a cell that belongs to cartilage tissue. It also goes by the name cartilage cell.
What is a chondrocyte?
Chondrocytes are cells that arise from chondroblast]s. They are also called chondrocytes and are found within cartilage tissue. Together with the intercellular substances, the chondrocytes are among the most important cartilage components. Although the chondrocyte is the only living part of cartilage, it only accounts for about one percent of cartilage tissue. Cartilage growth, also known as chondrogenesis, is differentiated between thickness growth (appositional growth) and length growth (interstitial growth). In interstitial growth, cartilage originates from mesenchyme. In this process, the mesenchyme cells differentiate into chondroblasts, which proliferate at a high rate. Cartilage matrix is produced by the chondroblasts. As long as the matrix is still soft, the new chondroblasts can move away from each other. In addition, further divisions occur. Once interstitial growth is complete, the resulting cartilage cells form isogenic groups, becoming chondrocytes that no longer have the ability to divide. During appositional growth, the perichondrium forms from the mesenchyme. This is the connective tissue cartilage skin. From the innermost layer, somatic cells differentiate into chondroblasts. Through them, a matrix is formed so that appositional growth occurs.
Anatomy and structure
Chondrocytes are round cells equipped with finger-like projections. Unlike other cells in the body, the chondrocyte has no communication capabilities. Since chondrocytes participate in the production of cartilage, connective tissue, as well as the extracellular matrix, they have a greater number of rough endoplasmic reticulum, which is used to synthesize proteins. Within the cartilage, chondrocytes are usually located individually in cartilage cavities. These are separated from the collagen fibers, special proteins, in the surrounding area. From the collagen fibers, several chondrocyte-cartilage cavities are grouped together to form chondrons, which are a higher unit. The attachment of the cell assemblies to the cartilage skin takes place through fibers located between the chondrons. The synovial fluid is responsible for supplying the chondrocytes with important nutrients. It is possible to both culture and isolate the chondrocytes. In order to regenerate cartilage, appropriate cultures can be fixed on special carrier material. In the case of cartilage, a distinction must be made between hyaline cartilage, elastic cartilage and fibrocartilage. Hyaline cartilage is the term used for articular cartilage, rib cartilage, nasal cartilage and tracheal cartilage. On this type of cartilage, which is the most common, the chondrocytes have an elliptical shape. Elastic cartilage, such as laryngeal cartilage or ear cartilage, is found rather rarely. The elastic chondrocytes are located in it either singly or in groups. Fibrocartilage is found, for example, in articular cartilage such as the temporomandibular joint. Here, the chondrocytes exhibit less elasticity and organize themselves into small groups. For the most part, however, they are found individually within the matrix.
Function and tasks
The tasks of chondrocytes primarily include the production of cartilage. In this process, they form the basic substance of cartilage, the extracellular matrix. In the context of human growth, they have the ability to divide cells, thus playing their part in cartilage growth. Because of their ability to divide, they are also capable of repairing minor cartilage damage. Once growth is complete, however, the chondrocytes lose their ability to divide. Thereafter, their function consists only of the formation of cartilage ground substance. They can then no longer carry out repairs to the cartilage. Together with reticulum cells, osteocytes and fibrocytes, chondrocytes belong to the fixed connective tissue cells. Their main functions are mechanical stability and secretion. Within chondrocytes, synthesis of RNA, DNA and protein (protein) occurs. In addition, stimulation of amino acids and cell proliferation take place. An increase in the activities of the chondrocytes is achieved by the hormones testosterone and thyroxine.Estradiol, cortisone, and hydrocortisone such as cortisol provide for their inhibition.
Diseases
Osteoarthritis represents a disease of chondrocytes that occurs frequently. This involves damage to the cartilage tissue. Osteoarthritis forms a wear and tear of the joint, which is not only caused by age. Affected individuals suffer from degenerative and inflammatory damage to the joints, which in turn can result in considerable pain. In osteoarthritis, the extracellular matrix proteins within the cartilage are degraded by proteases. It has not yet been possible to determine how this occurs. In order to treat osteoarthritis successfully, chondrocytes are transplanted into the patient. The treating physician removes chondrocytes from the diseased area during an arthroscopy. These can be multiplied in a laboratory over a period of 2 to 3 weeks. After this period has elapsed, the chondrocytes can be reinserted into the defective cartilage region. If the integration of the chondrocytes is successful, this eventually leads to improved mobility. Since the implanted chondrocytes originate from the patient’s body, the risk of rejection is very low. Achondroplasia is another disorder that affects chondrocytes. This is a mutation that occurs during the growth of the skeletal system. It leads to dwarfism, which is accompanied by shortening of the limbs and an unusually long trunk. Because the fibroblast growth factor chondrocyte receptor is insufficiently expressed in this process, there is a disruption of chondrocyte proliferation within the growth plate.
