Cartilage is a specialized form of connective tissue produced by differentiated fibroblast-like cells called chondrocytes. It is characterized by a prominent extracellular matrix consisting of various proportions of connective tissue fibers embedded in a gel-like matrix.
Chondrocytes are cells unique to cartilage and are located within lacunae (holes) in the matrix that they have built around themselves. Lacunae become separated from one another as a result of the secretory activity of the chondrocytes.
Three kinds of cartilage are classified according to the abundance of certain fibers and the characteristics of their matrix:
- Hyaline cartilage has a matrix composed of type II collagen and chondromucoprotein, a copolymer of chondroitin sulfates A and C with protein. Its high concentration of negatively-charged sulfate groups makes it appear intensely basophilic under H&E staining. This type of cartilage makes up the articular surface in joints.
- Fibrocartilage is distinguished by its high content and orderly arrangement of type I collagen fibers. It is typically located in regions where tendons attach to bones, the intervertebral discs, and the symphysis between certain bones.
- Elastic cartilage is characterized by the presence of abundant elastic fibers and is quite cellular. It is made up of type II collagen and is located in the pinna of the ear, the turbinates of the nose and the epiglottis.
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