Answer
Appositional growth of cartilage is growth that takes place by addition of new material on the outer surface of existing cartilage. Conversely, Interstitial growth takes place by formation of new tissue at several centers within existing tissue. This is only possible in pliable tissue.
Work Step by Step
The dense irregular connective covering of cartilage is called perichondrium. It has an outer and an inner layer. The cells of the outer layer are fibroblasts ; they produce collagen fibers. The inner perichondrial layer is called the chondrogenic layer because it is in this layer that growth takes place. Here the fibroblasts differentiate into chondroblasts. Chondroblasts lay down extracellular materials around themselves as the cartilage matures; then they differentiate into chondrocytes. The material laid down on existing cartilage surfaces results in increase in thickness or width of the cartilage. This type of appositional growth can only take place in flexible tissues.
Interstitial growth is produced in cartilage by chondrocytes in several lacunae. In this process, the chondrocytes divide rapidly and form cell nests. The cells secrete matrix which separates them from one another. Embedded within matrix, the chondrocytes continuously deposit more matrix around themselves. The increasing deposits, separate the cells farther and farther apart while simultaneously expanding the substance of the cartilage. This kind of increase in size of the tissue is called interstitial growth.
