Localization and Macroscopic Appearance
In a fresh, unfixed state, elastic cartilage is easily recognized by its characteristic yellowish tint. This color is imparted by the protein elastin, which is abundant in the extracellular matrix.
In the human body, elastic cartilage forms structures requiring high flexibility and the ability to return to their original shape after deformation. The main sites of localization include:
- Auricle (pinna) and external acoustic meatus;
- Specific parts of the larynx;
- Walls of the middle bronchi.
Similarities with Hyaline Cartilage
Despite functional differences, elastic cartilage shares a general structural plan with hyaline cartilage. The tissue is covered externally by the perichondrium, which performs trophic and kambial (growth) functions.
The cellular composition is represented by chondrocytes — large, oval-shaped cells whose cytoplasm appears light in microscopic sections. Deep within the tissue, chondrocytes are grouped into so-called isogenous groups — clusters of cells originating from a single precursor.
Histological Features
The main distinctive features of elastic cartilage lie in the organization of cellular groups and the composition of the matrix:
- Architectonics of isogenous groups. Unlike hyaline cartilage, chondrocytes here are most commonly arranged in pairs, closely apposed to one another. These cell clusters form characteristic "chains" that are oriented strictly perpendicular to the surface of the cartilage (the perichondrium).
- Composition of the extracellular matrix. The matrix is penetrated by a dense, multidirectional network of elastic fibers. Collagen fibrils are also present in the extracellular matrix, but their quantity is significantly lower than that of elastic fibers.
Routine staining with hematoxylin and eosin is insufficient for studying elastic cartilage under a microscope. A special stain, orcein, is used to selectively stain elastic fibers a rich dark cherry-red color.
Physiological Properties
A crucial physiological feature of elastic cartilage tissue is that it never undergoes calcification (mineralization). Deposition of calcium salts, which is typical for aging hyaline cartilage, does not occur here.
This resistance to calcification is explained by two factors highlighted in classic histology:
- Low collagen content in the extracellular matrix;
- Specific features of the trophic supply (nutrition) of this tissue.