Cartilage is a connective tissue in the body. This flexible and resilient material provides structural support, allowing for movement and cushioning. It reduces friction between bones and absorbs mechanical stress, supporting the musculoskeletal system.
What is Cartilage?
Cartilage is a connective tissue composed of cells called chondrocytes and an extracellular matrix. Chondrocytes produce and maintain this matrix, which consists of collagen and elastic fibers embedded in a ground substance of proteoglycans and glycosaminoglycans. These components give cartilage its characteristic strength, flexibility, and ability to resist compression.
Cartilage is avascular, meaning it lacks a direct blood supply. Unlike most other tissues, chondrocytes receive their nutrients through diffusion from the surrounding environment, primarily from synovial fluid in joints or from the perichondrium, a fibrous membrane that covers most cartilage. This reliance on diffusion contributes to the slow healing process of cartilage injuries. There are three main types of cartilage: hyaline cartilage, elastic cartilage, and fibrocartilage, each distinguished by its specific matrix composition and properties.
Key Locations and Functions of Cartilage
Hyaline Cartilage
Hyaline cartilage, the most common type, is found in many locations. It has a smooth, glassy appearance. It covers the ends of bones in synovial joints, such as the knees, hips, and shoulders, where it is known as articular cartilage. Here, it provides a low-friction surface, allowing bones to glide smoothly during movement, and acts as a shock absorber. Hyaline cartilage also provides flexible support in the nose, trachea, and bronchi, maintaining open airways.
Elastic Cartilage
Elastic cartilage, distinguished by its yellowish appearance and high concentration of elastic fibers, offers greater flexibility and returns to its original shape after bending. This type of cartilage is present in structures requiring pliability, such as the external ear, providing its shape while allowing it to bend without damage. It is also found in the epiglottis, which covers the windpipe during swallowing, and in the Eustachian tubes, connecting the middle ear to the back of the throat.
Fibrocartilage
Fibrocartilage is the strongest and least flexible type, containing a dense network of collagen fibers that give it tensile strength and resistance to compression. This cartilage is located in areas subjected to high mechanical stress and weight-bearing forces. Examples include the intervertebral discs between the vertebrae of the spine, where it absorbs shock and supports, and the menisci in the knee joint, which distribute pressure and stabilize the joint. Fibrocartilage is also found in the pubic symphysis, connecting the two halves of the pelvis, and at certain tendon and ligament attachments to bone.