Chondrocyte
Encyclopedia
Chondrocytes are the only cells found in cartilage
. They produce and maintain the cartilaginous matrix, which consists mainly of collagen
and proteoglycan
s. Although chondroblast
is still commonly used to describe an immature chondrocyte, use of the term is discouraged, for it is technically inaccurate since the progenitor of chondrocytes (which are mesenchymal stem cells) can also differentiate into osteoblast
s. The organization of chondrocytes within cartilage differs depending upon the type of cartilage and where in the tissue they are found.
When referring to bone or cartilage, mesenchymal stem cells (MSC) are commonly known as osteochondrogenic (or osteogenic, chondrogenic, osteoprogenitor, etc.) cells since a single MSC has shown the ability to differentiate into chondrocytes or osteoblast
s, depending on the medium. In vivo, differentiation of an MSC in a vascularized area (such as bone) yields an osteoblast
, whereas differentiation of an MSC in a non-vascularized area (such as cartilage) yields a chondrocyte. Chondrocytes undergo terminal differentiation when they become hypertrophic during endochondral ossification
. This last stage is characterized by major phenotypic
changes in the cell.
Cartilage
Cartilage is a flexible connective tissue found in many areas in the bodies of humans and other animals, including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs...
. They produce and maintain the cartilaginous matrix, which consists mainly of collagen
Collagen
Collagen is a group of naturally occurring proteins found in animals, especially in the flesh and connective tissues of mammals. It is the main component of connective tissue, and is the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content...
and proteoglycan
Proteoglycan
Proteoglycans are proteins that are heavily glycosylated. The basic proteoglycan unit consists of a "core protein" with one or more covalently attached glycosaminoglycan chain. The point of attachment is a Ser residue to which the glycosaminoglycan is joined through a tetrasaccharide bridge...
s. Although chondroblast
Chondroblast
A chondroblast is a cell which originates from a mesenchymal stem cell and forms chondrocytes, commonly known as cartilage cells. Chondroblasts that become embedded in the matrix are called chondrocytes. They lie in the space or lacunae present in the groups of two or more. The groups are formed by...
is still commonly used to describe an immature chondrocyte, use of the term is discouraged, for it is technically inaccurate since the progenitor of chondrocytes (which are mesenchymal stem cells) can also differentiate into osteoblast
Osteoblast
Osteoblasts are mononucleate cells that are responsible for bone formation; in essence, osteoblasts are specialized fibroblasts that in addition to fibroblastic products, express bone sialoprotein and osteocalcin.Osteoblasts produce a matrix of osteoid, which is composed mainly of Type I collagen...
s. The organization of chondrocytes within cartilage differs depending upon the type of cartilage and where in the tissue they are found.
Differentiation
From least- to terminally-differentiated, the chondrocytic lineage is:- Colony-forming unit-fibroblast (CFU-F)
- Mesenchymal stem cell / marrow stromal cell (MSC)
- Chondrocyte
- Hypertrophic chondrocyte
When referring to bone or cartilage, mesenchymal stem cells (MSC) are commonly known as osteochondrogenic (or osteogenic, chondrogenic, osteoprogenitor, etc.) cells since a single MSC has shown the ability to differentiate into chondrocytes or osteoblast
Osteoblast
Osteoblasts are mononucleate cells that are responsible for bone formation; in essence, osteoblasts are specialized fibroblasts that in addition to fibroblastic products, express bone sialoprotein and osteocalcin.Osteoblasts produce a matrix of osteoid, which is composed mainly of Type I collagen...
s, depending on the medium. In vivo, differentiation of an MSC in a vascularized area (such as bone) yields an osteoblast
Osteoblast
Osteoblasts are mononucleate cells that are responsible for bone formation; in essence, osteoblasts are specialized fibroblasts that in addition to fibroblastic products, express bone sialoprotein and osteocalcin.Osteoblasts produce a matrix of osteoid, which is composed mainly of Type I collagen...
, whereas differentiation of an MSC in a non-vascularized area (such as cartilage) yields a chondrocyte. Chondrocytes undergo terminal differentiation when they become hypertrophic during endochondral ossification
Endochondral ossification
Endochondral ossification is one of the two essential processes during fetal development of the mammalian skeletal system by which bone tissue is created. Unlike intramembranous ossification, which is the other process by which bone tissue is created, cartilage is present during endochondral...
. This last stage is characterized by major phenotypic
Phenotype
A phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...
changes in the cell.