Cartilage is a flexible, semi-rigid connective tissue found in various parts of the body. It is composed of specialized cells called chondrocytes, which produce and maintain the extracellular matrix consisting of collagen fibers, proteoglycans, and other structural proteins. It provides support, cushioning, and a smooth surface for the movement of joints, and it also serves as a structural component in the respiratory tract, ears, and other parts of the body.
There are three main types of cartilage, each with distinct properties and functions:
- Hyaline: This is the most common type, found in the nose, trachea, larynx, and on the surfaces of bones within synovial joints. It has a smooth, glassy appearance and provides a low-friction surface for joint movement. Hyaline cartilage is composed mainly of type II collagen and has a high concentration of proteoglycans, which provide resistance to compression.
- Fibrocartilage: Fibrocartilage is a tough, dense form of cartilage that contains a higher proportion of collagen fibers, primarily type I collagen. This type of cartilage is found in areas of the body where strong support and resistance to compression are required, such as the intervertebral discs, the pubic symphysis, and the menisci of the knee joint.
- Elastic: Elastic cartilage is found in the outer ear (auricle), the epiglottis, and the Eustachian tubes. It is characterized by the presence of numerous elastic fibers in addition to collagen fibers, which provide flexibility and resilience. Elastic cartilage allows these structures to maintain their shape while also permitting a degree of flexibility.
Cartilage is an avascular tissue, meaning it does not contain blood vessels. Nutrients and waste products are exchanged through diffusion between the cartilage and the surrounding tissue. This lack of direct blood supply contributes to the relatively slow rate of cartilage repair and regeneration when damaged. Damage to cartilage, such as that caused by osteoarthritis, can lead to pain, stiffness, and loss of joint function. Current research is focused on finding ways to improve cartilage repair and regeneration, including the use of tissue engineering and regenerative medicine techniques.