Chondroblaste

Chondroblasts, or perichondrial cells, is the name given to mesenchymal progenitor cells in situ which, from endochondral ossification, will form chondrocytes in the growing cartilage matrix. Another name for them is subchondral cortico-spongious progenitors. They have euchromatic nuclei and stain by basic dyes. These cells are extremely important in chondrogenesis due to their role in forming both the chondrocytes and cartilage matrix which will eventually form cartilage. Use of the term is technically inaccurate since mesenchymal progenitors can also technically differentiate into osteoblasts or fat. Chondroblasts are called chondrocytes when they embed themselves in the cartilage matrix, consisting of proteoglycan and collagen fibers, until they lie in the matrix lacunae. Once they embed themselves into the cartilage matrix, they grow the cartilage matrix by growing more cartilage extracellular matrix rather than by dividing further. Within adults and developing adults, most chondroblasts are located in the perichondrium. This is a thin layer of connective tissue which protects cartilage and is where chondroblasts help to expand cartilage size whenever prompted to by hormones such as GH, TH, and glycosaminoglycans. They are located on the perichondrium because the perichondrium, located on the outside of developing bone, is not as heavily ensheathed in cartilage extracellular matrix as the interior and because here where capillaries are located. The type of growth maintained by chondroblasts is called appositional bone growth and increases the birth of the affected tissue. It is important to note that perichondrium, and thus chondroblasts, are not found on the articular cartilage surfaces of joints. The extracellular matrix secreted by chondroblasts is composed of fibers, collagen, hyaluronic acid, proteoglycans, glycoproteins, water, and a host of macromolecules. Within finished cartilage, collagen fibers compose 10-20% of the volume, water 65-80%, and the proteoglycan-hyaluronic acid aggregates the remaining portion.