Cartilage

Cartilage is a flexible connective tissue found in many areas of the body in humans and other animals, including joints between bones, the rib cage, the ear, the nose, bronchial tubes, and intervertebral discs. It is not as hard and rigid as bone, but it is stiffer and less flexible than muscle.

Composition: Cartilage is primarily composed of specialized cells called chondrocytes, which are embedded in an extracellular matrix. This matrix consists of ground substance, which is rich in proteoglycans (specifically aggrecan, which binds to hyaluronic acid) and collagen fibers. The specific type and arrangement of collagen fibers vary depending on the type of cartilage.

Types of Cartilage: There are three main types of cartilage:

• Hyaline Cartilage: This is the most common type and is characterized by a glassy, translucent appearance. It contains moderate amounts of collagen and is found in articular surfaces of joints, the nose, trachea, and ribs. It provides smooth surfaces for joint movement and structural support.

• Elastic Cartilage: This type of cartilage contains a high concentration of elastic fibers in addition to collagen. This gives it significant flexibility and resilience. It is found in the external ear (auricle) and the epiglottis.

• Fibrocartilage: This is the toughest type of cartilage, containing a high proportion of collagen fibers arranged in thick bundles. It provides tensile strength and resistance to compression. It is found in intervertebral discs, menisci of the knee, and the pubic symphysis.

Function: Cartilage serves several important functions:

• Support: Provides structural support and shape to various body parts.
• Cushioning: Acts as a shock absorber in joints, protecting bones from impact.
• Smooth Movement: Reduces friction between bones in joints, allowing for smooth movement.
• Growth: Serves as a template for bone growth during development (endochondral ossification).

Vascularity and Repair: Cartilage is avascular, meaning it lacks a direct blood supply. This limited blood supply contributes to its slow healing and limited regenerative capacity. Nutrients and oxygen are supplied to chondrocytes via diffusion from the surrounding perichondrium (in some types) or synovial fluid (in articular cartilage). Damage to cartilage, especially in joints, can lead to osteoarthritis.