CHARACTERISTICS, COMPONENTS, AND CLASSIFICATION OF THE CARTILAGE TISSUE
Cartilage is a type of connective tissue composed of cells called chondrocytes and a large amount of extracellular matrix (ECM).
The cartilagenous matrix is stiffer than that of the connective tissue proper and the chondrocytes are housed in small cavities of the matrix called lacunae (plural of lacuna).
Cartilages come in three types: hyaline cartilage, elastic cartilage, and fibrous cartilage or fibrocartilage. These types differ in the arrangement of their chondrocytes and especially in the composition of their ECM.
The cartilage ECM has unique characteristics that differ from that of the connective tissue proper.
The fibrils of the hyaline cartilage ECM are thin and composed of type II collagen molecules. They are not organized into thick fibers and therefore not easilly visible under a light microscope. The fibers and fundamental matrix of the elastic cartilage contain a large amount of elastic material. In the fibrous cartilage the collagen fibers are made primarily of collagen type I molecules.
The fundamental ECM of the hyaline and elastic cartilage contains many proteoglycan and sulfated glycosaminoglycan molecules (e.g. chondroitin sulfate) and non-sulfated glycosaminoglycans (e.g. hyaluronate). They are primarily responsible for the rigidity of these tissues and their characteristic consistency. Water is a significant component of the cartilage ECM.
As the molecules of the cartilage fundamental ECM, especially that of the hyaline cartilage have many acidic radicals, it is preferentially stained by basic dyes. In sections stained with hematoxylin and eosin, this matrix shows a bluish color, unlike the matrix of the connective tissue proper, which is acidophilic and stains pink due to large amounts of thicker collagen fibers composed of collagen type I.
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