There are three types of cartilage, hyaline cartilage, fibrocartilage, and elastic cartilage. Cartilage grows by two process , appositional growth, and interstitial growth. Appositional growth occurs at the surfaces of cartilage. In contrast, interstitial growth takes place within already existing tissue. Appositional growth takes place in the inner layer of the perichondrial covering of hyaline, and elastic cartilage. Interstitial growth does not require a perichondrium. Appositional growth starts later in development ( than does interstitial growth), but it continues through adolescence into young adulthood. This is the case because as cartilage matures, and becomes more rigid , interstitial growth slows, then ceases. As a consequence, interstitial growth occurs mainly in the soft, pliable cartilage of childhood, and adolescence.
Work Step by Step
In appositional growth, chondroblasts, in the inner layer of the perichondrium, multiply mitotically, and differentiate into chondrocytes. Chondrocytes secrete an extracellular matrix composed of fibers ( collagen and elastin), and ground substance ( mainly of chondroitin sulfate). As synthesis, and secretion continues, more, and more matrix accumulates on the outer surfaces of the cartilage, causing it to increase in width. Interstitial growth, on the other hand, is effected by chondrocytes within lacunae of existing cartilage. Some of these chondrocytes retain limited capacities to divide, and secrete matrix. As more matrix is laid down between the cells, they are separated farther, and farther, resulting in increased diameter or depth of the tissue This kind of cartilage growth occurs mainly from childhood to adolescence. It is also part of the process by which long bones increase in length.