CHARACTERISTICS, COMPONENTS, AND CLASSIFICATION OF CARTILAGE TISSUE
Cartilage tissue is a type of connective tissue composed of cells called chondrocytes and a large amount of extracellular matrix (ECM).
The matrix of cartilage tissue has a more rigid consistency than that of connective tissue proper. The chondrocytes are housed in small cavities of the matrix called lacunae.
Cartilage tissue comes in three types: hyaline cartilage, elastic cartilage, and fibrous cartilage or fibrocartilage. These types differ in the arrangement of their chondrocytes and composition of the ECM.
The extracellular matrix of cartilage tissue has unique characteristics, different from those of connective tissue itself. In hyaline and elastic cartilage, the ECM collagen is composed primarily of type II collagen molecules. These molecules form collagen fibrils, but these are not organized into thick fibers and are therefore not visible under light microscopy. In the elastic type of cartilage, the ECM contains a large amount of elastic material and elastic fibers, in addition to collagen. In fibrous cartilage, the collagen is primarily type I.
The fundamental ECM of cartilage tissue, particularly in hyaline and elastic cartilage, contains many sulfated (e.g., chondroitin sulfate) and non-sulfated (e.g., hyaluronate) glycosaminoglycans. These molecules are primarily responsible for the rigidity of this tissue and its characteristic consistency.
Because there are many acidic radicals in the fundamental matrix, this matrix is preferentially stained by basic dyes. In sections stained with hematoxylin and eosin, the matrix has a bluish color, unlike the matrix of the connective tissue proper, which is acidophilic (pink) due to the presence of a large amount of collagen fibers.