B, bone

C, cartilage

CT, connective tissue

JC, joint cavity L, ligament

MC, marrow cavity arrowhead, calcified cartilage

Elastic cartilage has a matrix containing elastic fibers and elastic lamellae in addition to type II collagen. It is found in the auricle of the external ear, in the auditory tube, in the epiglottis, and in part of the larynx. The elastic material imparts properties of elasticity, as distinguished from resiliency, which are not shared by hyaline cartilage. Elastic cartilage is surrounded by perichondrium, and it, too, increases in size by both appositional and interstitial growth. Unlike hyaline cartilage, however, elastic cartilage does not normally calcify.

Figure 1, epiglottis, human, H&E and orcein stains x80.

This section of the epiglottis contains elastic cartilage (EC) as the centrally located structure. The essential components of the cartilage, namely, the matrix that stains deep blue and the light, unstained lacunae surrounded by matrix, are evident in this low-magnification micrograph. The perimeter of the cartilage is covered by perichondrium; its

Figure 2, epiglottis, human, H&E and orcein stains x250; inset x400.

This shows an area of the elastic cartilage at higher magnification. The elastic fibers appear as the blue, elongate profiles within the matrix. They are most evident at the edges of the cartilage, but they are obscured in some deeper parts of the matrix, where they blend with the elastic material that forms a honeycomb about the lacunae. Elastic fibers (E) are also in the adipose tissue (AT), between the adipocytes.

Some of the lacunae in the cartilage are arranged in pairs separated by a thin plate of matrix. The plate of matrix appears as a bar between the adjacent lacunae. This is a reflection of interstitial growth by the cartilage, in that the adjacent cartilage cells are derived from the same parent cell. They have moved away from each other and secreted a plate of cartilage matrix between them to form two lacunae.

fibrous character is just barely visible in this figure. Also note the adipose tissue (AT) within the boundaries of the elastic cartilage.

Both above and below the elastic cartilage is connective tissue, and each surface of the epiglottis is formed by stratified squamous epithelium (SE). Mucous glands (MG) are in the connective tissue in the bottom of this figure.

Most chondrocytes shown in this figure occupy only part of the lacuna. This is, in part, due to shrinkage, but it is also due to the fact that older chondrocytes contain lipid in large droplets that is lost during the processing of the tissue. The shrinkage of chondrocytes within the lacunae or their loss due to dropping out of the section during preparation causes the lacunae to stand out as light, unstained areas against the darkly stained matrix.

The inset shows the elastic cartilage at still higher magnification. Here, the elastic fibers (E) are again evident as elongate profiles, chiefly at the edges of the cartilage. Most chondrocytes in this part of the specimen show little shrinkage. Many of the cells display a typically rounded nucleus, and the cytoplasm is evident. Note, again, that some lacunae contain two chondrocytes, indicating interstitial growth.

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