Hyaline Cartilage

Discussion

• hyaline cartilage is the most common variety of cartilage;
• it is found in costal cartilages, articular cartilages, epiphyseal plates, & majority of fetal skeleton that is later replaced by bone;
• chondrocytes, occupy lacunae generously distributed through the matrix;
  • each peripheral lacuna typically houses a single chondrocyte;
  • deeper lacunae may contain two or more chondrocytes;
  • surrounding each cell is a territorial matrix w/ a higher concentration of proteoglycans;
• free surfaces of most hyaline cartilage (but not articular cartilage) are covered by a layer of fibrous connective tissue, perichondrium;
  • deep portion of perichondrium is composed of chondroblasts;
  • external portion is less cellular and more densely fibrous;
• approx 10% of wet weight of cartilage is collagen;
• approx 75% of matrix is water;
• remainder is a nonfibrous filler material;
• these entities together form stiff sol;
• cartilage contains predominantly type II collagens w/ lesser amounts of type IX and type XI;
• functions of collagen fibers w/ in cartilage:
  • provides tensile strength to the tissue and resist movement of interstitial water & proteoglycans from the cartilage, esp. while it sustains compressional loading;
  • to anchor ground substance of articular cartilage to subchondral bone;
• filler material of cartilage is composed of proteoglycan aggregates w/ chondroitin sulfate & keratan sulfate as chief glycosaminoglycans;
• much of hyaline cartilage of the body ultimately calcifies w/ maturation;
  • when calcification occurs, chondrocytes die & matrix disintegrates;
  • articular cartilage is unique in that its more superficial zones do not calcify, except in pathologic states such as pseudogout

Histology

• young chondrocytes & chondroblasts have rounded nuclei (or double nuclei);
• cytoplasm contains elongated mitochondria, well-developed Golgi apparatus, varying amounts of glycogen, & lipid droplets

References

• Medical Progress: Epiphyseal Disorders.
• The deleterious effects of drying on articular cartilage.
• The viability of articular cartilage in fresh osteochondral allografts after clinical transplantation.
• The effects of exposure of articular cartilage to air. A histochemical and ultrastructural investigation.
• The potential for regeneration of articular cartilage in defects created by chondral shaving and subchondral abrasion. An experimental investigation in rabbits.
• The induction of neochondrogenesis in free intra-articular periosteal autografts under the influence of continuous passive motion. An experimental investigation in the rabbit.