Cartilage Overview and Structure

Cartilage Overview

• Cartilage is strong and flexible, enduring force while bending
• It's avascular, obtaining nutrients from the perichondrium
• Composed of cells (chondrogenic, chondroblasts, chondrocytes), fibers, and extracellular matrix
• Forms the foundation for long bone growth
• Acts as a shock absorber and smooth surface for joint movement
• Plays a role in bone development before and after birth

Cartilage Cells

• Chondrogenic cells develop into chondroblasts
• Chondroblasts produce cartilage matrix and collagen type II, and mature into chondrocytes
• Chondrocytes reside in lacunae
• Chondrocytes are responsible for maintaining cartilage matrix

Cartilage Extracellular Matrix (ECM)

• ECM is composed of collagen and/or elastic fibers
• Abundant glycosaminoglycans (GAGs) and proteoglycans
• These components offer firmness and resistance to mechanical stress

Perichondrium

• Outer perichondrium—dense connective tissue, rich in type I collagen fibers, and blood vessels—covers hyaline and elastic cartilage
• Inner cellular layer contains chondrogenic and chondroblasts

Cartilage Avascularity

• Cartilage lacks blood vessels and nerves within its matrix
• Nutrients diffuse from the perichondrium through the matrix to chondrocytes
• Limited metabolic activity, slow healing

Cartilage Types

• Hyaline cartilage: Most common; found in fetal skeleton, epiphyseal plates, costal cartilage, articular surfaces of joints, respiratory passages
• Elastic cartilage: Similar to hyaline, but with elastic fibers; found in ear pinna, Eustachian tube, epiglottis, external auditory canal
• Fibrocartilage: Scant matrix, primarily type I collagen; found in intervertebral discs, pubic symphysis, attachments of tendons and ligaments

Cartilage Growth

• Interstitial growth: Growth from within cartilage by chondrocytes dividing and secreting matrix
• Appositional growth: Growth along the outside of cartilage by chondroblasts secreting matrix and differentiating into chondrocytes