Fibrocartilage is intermediate in character between hyaline cartilage and dense connective tissue.
1. Composition and organization. Fibrocartilage is characterized by abundant type I collagen fibers; at low magnification, it closely resembles dense connective tissue. The ground sub stance contains equal amounts of dermatan sulfate and chondroitin sulfate. The matrix immediately surrounding the chondrocytes resembles that of hyaline cartilage and contains some type II collagen. The chondrocytes are distributed in columnar isogenous groups between the densely packed type I collagen bundles. There is no distinguishable perichondrium.
2. Histogenesis and growth. At sites where strong mechanical stresses occur, fibrocartilage develops from dense regular connective tissue through the transformation of fibroblasts or fibroblast like precursors into chondrocytes. Fibrocartilage growth has not been closely examined.
3. Function and location. Fibrocartilage is always associated with dense connective tissue, and the border between the two is usually indistinct. Its combination of cartilaginous ground substance and dense collagen bundles allows fibrocartilage to resist deformation under great stress; it is important in attaching bone to bone and providing restricted mobility. Sites in humans include the annulus fibrosus of the intervertebral disks, the symphysis pubis, and certain bone-ligament junctions.
Fibrocartilage
Hyaline Cartilage
5. Repair. Repair of cartilage fractures involves invasion of the breach by mesenchymal stem cells from the perichondrium, which then differentiate into chondrocytes. If the gap is large. a dense connective tissue scar may form.
6. Function and location. Its ability to grow rapidly while maintaining its rigidity makes hyaline cartilage an ideal fetal skeletal tissue. As fetal cartilage is replaced by bone, hyaline cartilage remains in the epiphyseal plates at the ends of lone: bones, allowing these bones to lengthen between birth and adulthood. At all ages, hyaline cartilage without a perichondrium (articular cartilage) covers the articular surfaces of bone, where its resistance to compression and its smooth texture make it a good cushion and low-friction surface. Hyaline cartilage is the most abundant and widely distributed cartilage type in the body. The costal (rib) cartilages, most of the laryngeal cartilages, the cartilaginous rings supporting the trachea, and the irregular cartilage plates in the walls of the bronchi are hyaline cartilage.
Histogenesis - Hyaline Cartilage
3. Histogenesis, All cartilage derives from embryonic mesenchyme. During the development of hyaline cartilage, mesenchymal cells retract their cytoplasmic extensions and assume a rounded shape, becoming chondroblasts; at the same time, they become more tightly packed, forming a mesenchymal condensation, or precartilage condensation. The increased cell-to-cell contact stimulates cartilage differentiation, which progresses from the center outward. Chondroblasts at the core of the condensation are the first to secrete cartilaginous matrix materials, which separate the cells again. When it is completely surrounded by cartilage matrix, a chondroblast is termed a chondrocyte. Peripheral mesenchyme condenses around the developing cartilage mass to form the fibroblast-containing. dense, regular connective tissue of the perichondrium.
4. Growth. Cartilage grows by 2 distinct processes. Both involve mitosis and the deposition of additional matrix. Matrix synthesis is enhanced by growth hormone, thyroxine, and testesterone and is inhibited by estradiol and excess cortisone.
a. Interstitial growth involves the division of existing chondrocytes and gives rise to the isogenous groups, It is important in the formation of the fetal skeleton and continues in the epiphyseal plates and articular cartilages.
b. Appositional growth involves the differentiation into chondrocytes by chondroblasts and stem cells on the inner surface of the perichondrium. It is responsible for continued increase in the girth of the cartilage masses.