Cartilage Notes

Cartilage

Cartilage is a supportive connective tissue, similar to bone, comprising cells and an extracellular matrix. Its primary function is to support surrounding structures and maintain their environment.

Functions of Cartilage

  • Maintaining shape of structures.
  • Resisting compression.
  • Shock absorption.
  • Avoiding stretch and allowing recoil.
  • Providing smooth surfaces to minimize friction, particularly in joints.
    • Example: Articular cartilage at the distal end of the humerus (elbow) provides a smooth surface and reduces friction, preventing bone-on-bone contact during joint movement.

Cartilage Cells

  • Chondroblasts: Cells that produce the cartilage matrix.
    • Analogy: Similar to osteoblasts in bone tissue.
  • Chondrocytes: Mature chondroblasts that have become embedded in the cartilage matrix.
    • Function: Regulating the environment within the cartilage.
    • Location: Reside within lacunae (small cavities) in the cartilage.
    • Nutrient Transport: Cartilage matrix allows for passive diffusion of nutrients, eliminating the need for cellular projections (canaliculi) as seen in bone.
  • Matrix Components:
    • Collagen type II: Softer and more delicate compared to collagen type I in bone.
    • Chondroitin: A water-retaining material that contributes to the rubbery texture of cartilage.

Avascularity of Cartilage

  • Cartilage is avascular, meaning it lacks blood vessels.
  • Nutrient supply occurs via passive diffusion from the surrounding environment.
    • Synovial fluid in joints provides nutrients.
  • Rationale for Avascularity:
    • Presence of blood vessels in joints would risk damage during movement (pinching, tearing), leading to hematoma, bleeding, and reduced joint integrity.

Types of Cartilage

1. Hyaline (Articular) Cartilage
  • Appearance: Clear, glassy, and fine in texture.
  • Location: Ends of long bones in joints.
  • Function: Provides a smooth surface, reducing friction and preventing pain.
    • Prevents bone-on-bone contact, which would cause damage, inflammation, and pain.
  • Other Locations:
    • Trachea: C-shaped bands of hyaline cartilage keep the trachea open for air passage.
    • Knee joint: Articular cartilage between the patella (a sesamoid bone) and other joint surfaces.
2. Fibrocartilage
  • Characteristics: Fibrous in nature, containing dense collagen bundles.
  • Function: Provides strength and resistance against compression and shock.
  • Location: Areas needing support and integrity rather than smooth movement.
    • Intervertebral discs: Pads between vertebral bodies that absorb shock from walking, jumping, and running.
  • Chondrocytes arrangement: Often aligned in rows within lacunae, surrounded by collagen bundles.
3. Elastic Cartilage
  • Composition: Contains numerous elastic fibers arranged in a web-like structure.
  • Properties: Allows stretching and recoil while maintaining shape.
  • Function: Provides flexible support.
  • Location:
    • Ear: Maintains the shape of the ear, allowing it to return to its original form after being stretched or pulled.
    • Epiglottis: Flap that covers the trachea during swallowing to prevent food from entering the airway; directs food into the esophagus.