XII. CARTILAGE AND BONE  

A. Hyaline Cartilage  

Slide 43 (trachea)  

Hyaline cartilage is a firm but flexible connective tissue. It is composed of chondroblasts and chondrocytes, a matrix rich in proteoglycans and collagen fibers. Most bones are formed by the replacement of hyaline cartilage templates in the embryo  (endochondral bone formation). Cartilage including hyaline cartilage grows by the addition of materials to the surface or perichondrium by appositional growth.  

Cartilage may also grow by addition of material within the mass of tissue by interstitial growth. The collagen fibers in hyaline cartilage are not visible in the light microscope. Fibrils are revealed by  EM but they are only 6-25 nm in diameter and exhibit periodicity (banding).  

Following fixation and paraffin embedding there is shrinkage of the matrix, the lacunae seen in cartilage are shrinkage artifacts. These lacunae are not seen in well preserved material for EM.  Examine the slides that demonstrate hyaline cartilage and identify the perichondrium, chondrocytes, lacunae, collagen fibers, ground substance, and cell nests or groups of chondrocytes.   

B. Fibrocartilage  

Slide 9 (white fibrocartilage) 

Fibrocartilage is more resistant to pressure, compression, and tension than hyaline cartilage. The collagen fibers are prominent in fibrocartilage. Fibrocartilage is considered a transitional tissue between dense fibrous connective tissue and cartilage. It often merges with tendons and ligaments. Examine the slide of intervertebral disks. Note the collagenous fibers in the matrix. How do the lacunae compared with those seen in hyaline cartilage.  

C. Elastic Cartilage  

Slide 8 (elastic cartilage of epiglottis)  

Elastic cartilage is more flexible than hyaline cartilage. The chondrocytes are prominent in elastic cartilage. It contains bundles of elastic fibers and plates of elastic substance. It appears similar to hyaline cartilage except that there are large numbers of elastic fibers in the matrix. Examine the slide of elastic cartilage and note the presence and appearance of these elastic fibers.   

D. Bone  

Slide 56, 11 (dry ground bone, decalcified bone) 

Bone is a hard, rigid connective tissue containing bone cells, matrix and collagen fibers. When the inorganic salts are removed, bones are flexible. A decalcified long bone can be bent and even tied into a knot. Regardless of the shape, bones are all made of both compact and spongy parts. Compact bone forms most of the shafts of long bones. It is dense and solid looking, but contains cells and vessels. Within the compact bone are the longitudinally oriented units called haversian systems.   

In the center of each of these is a haversian canal containing blood vessels.  Around the canal are concentric layers or lamellae composed of minerals, fibers, matrix and cells in a highly ordered arrangement. Vessels reach the haversian canals from the periosteum, marrow cavity, or from the

Volkmann's canals. The osteocytes within the osteons reside in lacunae and are joined with adjacent lacunae through canaliculi which provide pathways for the exchange of nutrients, gases and wastes.   

Spongy bone or cancellous bone is full of channels and a network of delicate bony processes or trabeculae. The trabeculae contain the osteocytes in lacunae but the bony lamellae are irregular. Examine the slide of dry ground bone and decalcified bone and identify the cells or structures discussed above. Also examine the demonstration micrographs.