Histology of Elastic Cartilage
Elastic cartilage, sometimes referred to as yellow fibrocartilage, is a type of cartilage that provides both strength and elasticity to certain parts of the body, such as the ears. Within the outer ear, it provides the skeletal basis of the pinna, as well as the lateral region of the external auditory meatus. Elastic cartilage is also found in the epiglottis, as well as the corniculate and cuneiform laryngeal cartilages. Moreover, the walls of the medial part of the auditory canal is made up of elastic cartilage. It also allows structures to maintain their own specific shapes, easily reverting back to its original shape after being deformed. For example, if you pull or bend your ear, it will revert back to its natural shape when you let go.
Cartilage is made up of specialised cartilage cells called chondrocytes. In elastic cartilage, they are organised into elastic fibers, which make up a threadlike network or matrix. This matrix is composed of glycosaminoglycans, proteoglycans and multiadhesive glycoproteins. It is combined with elastic lamellae, and type II collagen. Elastic cartilage has a perichondrium, which is a layer of dense irregular connective tissue that surrounds cartilage that is independent from a joint.
When elastic cartilage is stained, you can see its elastic fibers. Elastic cartilage has to be specially stained to show the elastic fibers. This is because when stained with a haematoxylin and eosin (H&E) stain, the elastic fibers appear to look the same as hyaline cartilage. Hyaline cartilage is a translucent white type of cartilage present in areas of the body such as the joints. The main difference between this type of cartilage and elastic cartilage is that elastic cartilage contains many elastic fibers, whilst hyaline cartilage contains a matrix of mainly collagen fibers. Therefore to avoid confusion, a Verhoeff van Gieson stain is often used as this stains elastic fibers black. Elastic fibers also stain well in aldehyde fuchsin stains, Weigert’s elastic stains, and orcein stains.
When stained, the main components of elastic cartilage appear dark blue. Meanwhile, the lacunae (cavities) that are surrounded by matrix appear lighter. The blue elastic fibers are most visible around the edges of the cartilage, and appear elongated in shape. They are often difficult to see when they are deeper within the matrix. Some lacunae are organised into pairs and are divided by a fine plate of matrix. This plate can be clearly seen between the two lacunae. It forms as a result of the lacunae secreting cartilage matrix between themselves.
Unfortunately, when elastic cartilage is stained, the lipid within the chondrocytes becomes lost during the process of preparation, meaning that the chondrocytes often appear smaller than they should do. The chondrocytes are however visible within the lacunae, they are simply reduced in size. Unlike hyaline cartilage, which calcifies with aging, the matrix of elastic cartilage does not calcify during the aging process.