Plate 12 Spongy And Compact Bone

Hematoxylin and eosin (H&E)-stained sections of decalcified bone exhibit all of the formed soft tissue components that are seen in other dense connective tissues and allow one to distinguish the several cell types found in developing and mature bone. Such preparations also allow the use of special stains and histochemical methods to study bone development and function in more detail than is possible with H&E sections.

Figure 1, bone, monkey, H&E x80; upper inset x175.

This figure shows a decalcified section of two bones framing a joint cavity. Articular cartilage (AC) covers the surfaces that contact the neighboring bone. The free surface of each cartilage presents a relatively smooth contour, whereas the junction between the cartilage and the bone (SB) is irregular.

The articular cartilage is hyaline (upper inset). It shows the characteristic features of hyaline cartilage seen in Plate 7, page 173, namely, chondrocytes in lacunae, a homogeneous avascular matrix (homogeneous in that it presents no formed elements visible in the light microscope), and variable staining of the matrix. At least some of the cartilage cells are in lacunae that are close to each other, suggesting that they are daughter cells of the same parent cell.

The bone under the articular cartilage is spongy bone. It consists of spicules or trabeculae of bone tissue as well as marrow spaces (M). In this sample, the marrow consists primarily of adipose tissue. In addition to the marrow spaces, the bone tissue also contains space or tunnels for blood vessels (BV); in this respect, bone differs fundamentally from the hyaline cartilage on the articular surface, which is avascular. The essential features of the bone tissue are seen at higher magnification in the upper inset. These are osteocytes (Oc) in lacunae, an eosinophilic matrix, and blood vessels (BV). The spongy bone shown in this figure is nonlamellar; i.e., the matrix is not organized as lamellae, but rather, the collagen fibers are in the form of interwoven bundles. Certain features of woven nonlamellar bone are also displayed in the upper inset; namely, the cells are unevenly and randomly dispersed and are not arranged in an oriented pattern around the blood vessels. For comparison, note how the lacunae (and, therefore, also the osteocytes) display an oriented pattern about the Haversian canal in Figure 2 of Plate 11.

Figure 2, bone, monkey, H&E x80; lower inset x350.

This figure shows the shaft of a long bone. The center of the bone consists of a large marrow cavity (M) filled chiefly with adipose tissue; surrounding the marrow cavity is the bone tissue of the shaft. It is compact bone (CB). Although the compact bone tissue contains tunnels for blood vessels (BV), it does not contain marrow spaces. On its outer surface, the bone tissue is covered by a periosteum (Po), and its inner surface is covered by endosteum (Eo, lower inset). The en-dosteum consists of several layers of cells (nuclei of these cells are evident) and collagenous fibers. The endosteal cells have the potential to develop into osteoblasts (as do periosteal cells) if the need should arise, e.g., in fracture repair.

Histologically, the compact bone shown in this figure displays three characteristics: an eosinophilic matrix; lacunae in which osteocytes are located; and vascular tunnels (BV). The osteocytes (Oc) are identified chiefly by their nuclear staining, which stands out in contrast to the surrounding eosinophilic matrix. The boundaries of the lacunae and the canaliculi radiating from them (see Plate 11) are not evident.

In the adult human, compact bone is organized chiefly as Haversian systems or as other forms of lamellar bone. Although this form of bone tissue is readily seen in well-oriented ground sections, it is not always easy to identify in decalcified sections. It is particularly difficult to make this identification in longitudinal decalcified sections of a long bone as shown in this figure.

Was this article helpful?

0 0

Post a comment