Cartilage Overview and Structure

Cartilage Overview

• Cartilage is a specialized connective tissue (CT) lacking blood vessels (avascular).
• Its matrix is firm and resilient, like rubber.
• Cartilage provides support, keeps air passages open, provides smooth joint surfaces, and acts as a shock absorber.

Learning Objectives

• Define cartilage
• Classify cartilage
• List cartilage locations in the human body
• Describe cartilage microstructure

Cartilage Structure

• Cartilage is made of cells, fibers, and ground substance (matrix).
  • Cells:
    • Chondrogenic cells (mother cells for all cartilage cell types)
    • Chondroblasts (immature cartilage cells): located on the surface of cartilage and perichondrium. Secrete cartilage matrix and fibers.
    • Chondrocytes (mature cartilage cells): mature cells that secrete matrix, are completely surrounded by matrix, and are imprisoned in lacunae. Often found in groups of 2, 4, or 8 cells (cell nests).
  • Fibers: Collagen and elastic fibers, type varies with cartilage type.
  • Matrix: Rubber-like, basophilic (dark-staining), composed of glycosaminoglycans (GAGs), glycoproteins, and water.

Types of Cartilage

• Classified based on the fibers embedded in the matrix:
  • Hyaline cartilage: rich in collagen type II fibers, found in fetal skeletons, epiphyseal plates, articular surfaces, and respiratory passages (nose, trachea).
  • Elastic cartilage: contains elastic fibers, found in the ear pinna, Eustachian tube, epiglottis, and external auditory canal.
  • Fibrocartilage: has thick parallel bundles of collagen type I fibers, present in intervertebral discs, symphysis pubis, mandibular joint, sternoclavicular joint, and acetabulum.

Hyaline Cartilage (Structure)

• Surrounded by perichondrium (except at articular surfaces)
• Fibers: collagen type II
• Matrix: abundant, basophilic
• Produced by chondroblasts

Elastic Cartilage (Structure)

• Perichondrium present
• Fibers: elastic fibers forming a network within matrix
• Matrix: less abundant than in hyaline cartilage

Fibrocartilage (Structure)

• No perichondrium
• Fibers: collagen type I, thick parallel bundles
• Cartilage cells: present in rows between bundles
• Matrix: very scanty

Additional Notes

• The reference used is "Junqueira's Basic Histology, 13th Edition, 2013" by Anthony L. Mescher.