Structure and Properties of Cartilage

Cartilage Structure and Function

• Cartilage is a type of connective tissue characterized by the absence of blood vessels, lymphatic vessels, and nerves in adults (although young animals have blood vessels in growing cartilage)
• Supports soft tissues (e.g., ear, eyelid, trachea, and bronchi) and is essential for longitudinal bone growth through endochondral ossification
• Composed of chondrocytes embedded in an amorphous gel-like substance and connective tissue fibers, making it resilient

Chondrogenesis

• Embryonic mesenchyme gives rise to chondroblasts, which produce cartilage matrix
• Chondroblasts differentiate into chondrocytes, which are embedded in lacunae within the cartilage matrix
• Cartilage growth occurs through the multiplication of chondrocytes and the production of cartilage matrix

Types of Cartilage

• Hyaline cartilage: most common type, found in joints, growth plates, and respiratory tree
  • Locations: joints, growth plates, ribs, physes, nose, larynx, tracheal rings, and bronchi
• Elastic cartilage: found in the epiglottis, corniculate and cuneiform processes of the arytenoid cartilage, external auditory canal, and ear pinna
• Fibrocartilage: found in intervertebral discs, menisci, insertions of tendons and ligaments, mandibular symphysis, and pubic symphysis
  • Lacks perichondrium, thus does not have regenerative capacity

Cartilage Matrix

• Composed of collagen, elastic fibers, and proteoglycans (GAGs)
• GAGs are responsible for the basophilia of cartilage matrix
• Matrix near chondrocytes (territorial) is more basophilic due to the greater amount of GAGs

Tendons and Ligaments

• Tendons: connect muscles to bones, composed of parallel bundles of type I collagen fibers, 1-5% proteoglycans, and 2% elastin
• Ligaments: connect bones to bones, provide stability to joints

Joints

• Composed of articular cartilage, synovial membrane, and synovial fluid
• Articular cartilage: smooth surface, formed by type II collagen and proteoglycans, lacks blood vessels and nerves
• Synovial membrane: thin membrane with many villi, lined by specialized cells (synoviocytes - type A and type B)
• Synovial fluid: clear, viscous, colorless or slightly yellow fluid produced by synoviocytes, functions as a lubricant, protectant, and nutrient to joints