Cartilage
Cartilage is a specialised type of connective tissue, distinguished by its firm consistency and ability to withstand mechanical stress without permanent distortion. It lacks blood vessels, meaning that nutrients reach the chondrocytes through diffusion. There are three primary types: hyaline cartilage, elastic cartilage, and fibrocartilage, each adapted to specific functions in the body.
Elastic Cartilage
Elastic cartilage, similar in structure to hyaline cartilage, is characterised by a rich network of elastic fibres in its matrix. These fibres, in addition to type II collagen, contribute to the flexibility and resilience of elastic cartilage. Fresh elastic cartilage has a yellowish colour due to the abundance of elastic fibres.
Elastic cartilage is found in:
- the external ear (auricle),
- walls of the external auditory canals,
- auditory (Eustachian) tubes,
- epiglottis,
- cuneiform cartilage of the larynx.
Like hyaline cartilage, elastic cartilage is surrounded by a perichondrium.
Fibrocartilage
Fibrocartilage is a blend of hyaline cartilage and dense connective tissue. It can be considered a transitional form between these two tissue types. Fibrocartilage lacks a distinct perichondrium.
Fibrocartilage is characterised by:
- Chondrocytes: They occur singly or in isogenous groups, often arranged in rows.
- Matrix: It is less abundant than in hyaline or elastic cartilage and contains both type I and type II collagen. Type I collagen is concentrated in dense bundles, giving fibrocartilage its strength and rigidity. The matrix also has fewer proteoglycans, resulting in a more acidophilic staining pattern compared to other cartilage types.
Fibrocartilage is found in regions of the body subjected to significant tensile forces, including:
- intervertebral discs,
- attachments of certain ligaments,
- pubic symphysis.
In intervertebral discs, fibrocartilage functions as a shock absorber, protecting the vertebrae from damage. The annulus fibrosus, the outer region of the disc, is particularly rich in type I collagen, providing strength and resilience. The central nucleus, with its gel-like matrix rich in hyaluronic acid, further enhances the shock-absorbing capacity of the intervertebral disc.