Histo.4

• Cartilage


  A special form of connective tissue that develops from the mesenchyme
• Components of cartilage


  • Cells (chondrocytes and chondroblasts)
  • Extracellular matrix
• Cartilage


  • Nonvascular (avascular) and receives its nutrition via diffusion through the extracellular matrix
  • Exhibits tensile strength, provides firm structural support for soft tissues, allows flexibility without distortion, and is resilient to compression
• Types of cartilage


  • Hyaline cartilage
  • Elastic cartilage
  • Fibrocartilage
• Chondroblasts


  Embryonic cartilage producing cells
• Chondrocytes


  Lie in spaces (or lacunae) present in the matrix, synthesize and maintain all ECM components
• Chondrocyte maturation


  1. Small and show features of metabolically active cells at first

  2. Enlarge, often reaching a diameter of 40 μm or more as they mature

  3. Nuclei become heterochromatic and organelles become less prominent

  4. Cytoplasm may contain glycogen and lipids
• Components of ground substance


  • Proteoglycans (containing proteins and carbohydrates)
  • Glycosaminoglycans (chondroitin sulphate, keratin sulphate, hyaluronic acid)
  • Aggrecan core protein
• Proteoglycan molecules


  Tightly bound, along with the water content, form a firm gel that gives cartilage its firm consistency
• Chondronectin


  An important component of cartilage matrix, binds to GAGs, collagen, and integrins, mediating the adherence of chondrocytes to the ECM
• Fibers of cartilage


  • Collagen (type II)
  • Elastic fibers
• Perichondrium


  A layer of dense connective tissue that covers all hyaline cartilage except in the articular cartilage of joints, essential for the growth and maintenance of cartilage
• Perichondrium


  • Outer region consists of collagen type I fibers and fibroblasts, inner layer contains mesenchymal stem cells that provide a source for new chondroblasts
• Hyaline cartilage


  • Homogeneous and semitransparent, extracellular matrix is homogeneous with type II collagen and aggrecan, major cells are chondrocytes and chondroblasts
• Arrangement of chondrocytes in hyaline cartilage


  Isolated or in small isogenous groups towards the center, small and elongated towards the periphery, indistinguishable from fibroblasts just under the perichondrium
• Territorial matrix


  Newly formed matrix immediately around lacunae housing individual chondrocytes, and around cell nests, stains deeper
• Interstitial matrix


  Pale staining matrix separating cell nests
• Locations of hyaline cartilage in adults


  • Articular surfaces of movable joints
  • Walls of larger respiratory passages
  • Ventral ends of ribs
  • Epiphyseal plates of long bones
• Role of hyaline cartilage in bone growth


  Epiphyseal plate connects epiphysis to diaphysis, essential for longitudinal bone growth
• Functions of hyaline cartilage


  • Provides smooth, low-friction surfaces in joints
  • Structural support for respiratory tract
• Calcification of hyaline cartilage is often seen in old people, but not in elastic cartilage and fibrocartilage</b>
• Elastic cartilage


  • Contains an abundant network of elastic fibers in addition to collagen type II, more flexible and readily recovers its shape after being deformed
• Locations of elastic cartilage


  • Auricle of the ear
  • Walls of the external auditory canals
  • Auditory (Eustachian) tubes
  • Epiglottis, and the upper respiratory tract
• Fibrocartilage


  • A mingling of hyaline cartilage and dense connective tissue, found in intervertebral discs, attachments of certain ligaments, and the pubic symphysis
• Chondrocytes of fibrocartilage


  Occur singly and often in aligned isogenous aggregates, producing type II collagen and other ECM components, although the matrix around these chondrocytes is typically sparse
• Fibrocartilage matrix


  • Areas with chondrocytes and hyaline matrix are separated by regions with fibroblasts and dense bundles of type I collagen, more acidophilic than hyaline or elastic cartilage, no distinct surrounding perichondrium
• Cartilage formation, growth, and repair


  1. Forms from embryonic mesenchyme through chondrogenesis, enlarges by interstitial growth (mitotic division of chondrocytes) and appositional growth (chondroblast differentiation from perichondrium)

  2. Damaged cartilage undergoes slow and often incomplete repair, primarily dependent on cells in the perichondrium
• The poor capacity of cartilage for repair or regeneration is due in part to its avascularity and low metabolic rate