FIGURE 7.4 • Photomicrograph of a typical hyaline cartilage specimen stained with H&E. The upper portion of the micrograph shows the dense connective tissue (DCT ) overlying the perichondrium (P), from which new cartilage cells are derived. A slightly basophilic layer of growing cartilage (GC) underlying the perichondrium contains chondroblasts and immature chondrocytes that display little more than the nucleus residing in an empty-appearing lacuna. This layer represents deposition of new cartilage (appositional growth) on the surface of the existing hyaline cartilage. Mature chondrocytes with clearly visible nuclei (N) reside in the lacunae and are well preserved in this specimen. They produce the cartilage matrix that shows the dark-staining capsule or territorial matrix (TM) immediately surrounding the lacunae. The interterritorial matrix (IM) is more removed from the immediate vicinity of the chondrocytes and is less intensely stained. Growth from within the cartilage (interstitial growth) is reflected by the chondrocyte pairs and clusters that are responsible for the formation of isogenous groups (rectangles). 480.
FIGURE 7.5 • Photomicrograph of young, growing cartilage.
This specimen was preserved in glutaraldehyde, embedded in plastic, and stained with H&E. The chondrocytes, especially those in the upper part of the photomicrograph, are well preserved. The cytoplasm is deeply stained, exhibiting a distinct and relatively homogeneous basophilia. The clear areas (arrows) represent sites of the Golgi apparatus. 520.
However, the matrix does not stain homogeneously. Rather, three different regions are described based on the staining property of the matrix (Fig. 7.7).
 The capsular (pericellular) matrix is a ring of more densely staining matrix located immediately around the chondrocyte (see Fig. 7.4). It contains the highest concentration of sulfated proteoglycans, hyaluronan, bigly-cans, and several multiadhesive glycoproteins (e.g., fibronectin, decorin, and laminin). The capsular matrix contains almost exclusively type VI collagen fibrils that form a tightly woven enclosure around each chondrocyte. Type VI collagen binds to integrin receptors on the cell surface and anchors the chondrocytes to the matrix. A higher concentration of type IX collagen is also present in the capsular matrix.
 The territorial matrix is a region that is more removed from the immediate vicinity of the chondrocytes. It surrounds the isogenous group and contains a randomly arranged network of type II collagen fibrils with smaller quantities of type IX collagen. It also has a lower concentra-
FIGURE 7.6 • Electron micrograph of a young, active chondrocyte and surrounding matrix. The nucleus (N) of the chondrocyte is eccentrically located, like those in Figure 7.5, and the cytoplasm displays numerous and somewhat dilated profiles of rER, Golgi apparatus (G), and mitochondria (M). The large amount of rER and the extensive Golgi apparatus indicate that the cell is actively engaged in the production of cartilage matrix. The numerous dark particles in the matrix contain proteoglycans. The particularly large particles adjacent to the cell are located in the region of the matrix that is identified as the capsule or territorial matrix. 15,000. (Courtesy of Dr. H. Clarke Anderson.) tion of sulfated proteoglycans and stains less intensely than the capsular matrix. The interterritorial matrix is a region that surrounds the territorial matrix and occupies the space between groups of chondrocytes.
In addition to these regional differences in the concentration of sulfated proteoglycans and distribution of collagen fibrils, there is a decrease in proteoglycan content that occurs as cartilage ages, which is also reflected by staining differences.
Hyaline cartilage provides a model for the developing skeleton of the fetus.