Year: 2012
Type: book-chapter
Abstract: Recognition 568 Articular chondrocytes and zonal organisationArticular cartilage is organised to allow its main role to occur, that is, providing a smooth almost frictionless surface for pain-free mobility but also as a biomaterial that can also withstand compressive and shear forces.As well as the actual biochemical content of articular cartilage, the biomechanical properties rely on the structural organisation of the extracellular matrix and the cells embedded within them.The structure and organisation of articular cartilage not only varies with depth from the articular surface (divided into zones) but also the location within the joint (for example, weightbearing versus non-weightbearing surfaces).Articular chondrocytes occupy 2-5% of the tissue volume and are sometimes considered relatively inactive metabolically due to an absence of a vascular supply but are responsible for maintaining the integrity of the extracellular matrix and can respond to mechanical stimuli, growth factors and cytokines.Articular cartilage has four distinct histological and biochemical zones (I-IV): superficial (tangential), intermediate (transitional), deep (radial) and calcified.The superficial zone is the thinnest along the articular surface and merges with the perichondrium at the articular margin.Type II collagen in the superficial zone is orientated tangentially to the articular surface to provide resistance to tensile forces.Proteoglycan composition in this zone acts as a non-selective barrier to diffusion of oxygen and water and a selective barrier to the diffusion of nutrients and hormones.This is largely due to the large amount of negatively charged anionic groups on the sulphated side chains on proteoglycans which allows smaller, non-ionic molecules through the matrix more readily than larger charged molecules.The pericellular matrix in the chondron (the chondrocyte and its pericellular microenvironment) consists of high levels of collagen type VI and aggregating proteoglycans and defines the physiochemical environment of the chondrocyte (Wang et al, 2008) and biochemical or mechanical signals perceived by the chondrocyte are therefore influenced by the structural and functional composition of the chondron (Guilak et al., 2006).Proteoglycans in the pericellular zone are thought to have a role in binding the chondrocyte to the matrix rather that the direct biomechanical role seen in the interterritorial matrix.Within the matrix surrounding the chondrocytes (territorial matrix) are thin type II and VI collagen fibrils, organised in a "basket-weave" formation and these fibrils extend out in a parallel arrangement to bind with larger type II collagen fibrils in the interterritorial matrix.In the intermediate zone the chondron structure is more typical.In this zone the collagen fibrils appears more widely spaced and their orientation is more random and there are increased amounts of proteoglycan compared to the superficial zone.In the deep zone the chondrocytes start to align themselves in columns perpendicularly to the joint surface along with thicker collagen fibrils.The collagen fibrils are orientated radially between these chondrocytic columns.The abundant proteoglycan within the interterritorial matrix with higher amounts of keratin sulphate side chains increases the permeability of the matrix in the deep zone and may be important in allowing diffusion of nutrients to the deeper layers of cartilage.Between the deep and calcified zones, there is a demarcation consisting of mineral associated with matrix vesicles within the interterritorial matrix and this is known as the tidemark. The extracellular matrixThe extracellular matrix is a mechanically resilient structure comprising of collagens, proteoglycans and other non-collagenous proteins (Wilkins et al., 2000).Hydrated www.intechopen.com Cellular Physiology of Articular Cartilage in Health and Disease How to referenceIn order to correctly reference this scholarly work, feel free to copy and paste the following:
Source: InTech eBooks
DOI: 10.5772/28379
Authors: Peter I., Robert J., John S.
Language: English
Subfield: Rheumatology
Field: Medicine
Domain: Health Sciences
Open Access status: hybrid
OpenAlex ID: W2133214820