Transitions in collagen types during endochondral ossification in human growth cartilage

Immunohistochemical staining for Types I and II collagen in human growth cartilage showed that cartilage matrix consists of Type II collagen, whereas bone matrix contains Type I collagen. Endochondral ossification began with the deposition of Type I collagen by cells derived from bone marrow on the surface of the eroded cartilage. However, territorial matrix of the last hypertrophic chondrocytes contained both Types I and II collagen, thereby indicating that the degenerating chondrocytes initiate the synthesis of Type I collagen. This matrix, consisting of Types I and II collagen, is then replaced by newly formed osteoid.