Skeletal 3

• Cartilage

  A major component of ALL vertebrate skeletons, irrespective of whether they also have bone

  
• Cartilage

  • Chondroblasts deposit ECM, which may or may not be mineralized with calcium phosphate
  • It supports and lines articular surfaces
  • Forms the support of certain structures in the body (e.g., nose, ears)
• Chondrocytes lack cellular processes - no interconnections (canaliculi) – isolated
• Cartilage is avascular
• Embryonic origins of cartilage

  Both mesoderm and neural crest (and often interactions between them)
• Cartilage can fossilize, while not as easily preserved as bone in the fossil record, it is not uncommon</b>

  
• Cartilage

  • Light
  • Flexible
  • Elastic
  • High damping potential
  • Not brittle like bone (it "gives" slightly)

  
• Cartilage has indeterminate growth
• Structures comprised principally of cartilage

  • Ears
  • Nose

  
• Extracellular gel (ECM) of skeletal cartilage

  • Water (up to 80% total weight)
  • Type II collagen (up to 60% dry weight)
  • Proteoglycans (~10% dry weight), of which, most is aggrecan (chondroitin sulfate proteoglycan 1)
• Extracellular matrix has variable collagen/proteoglycan content depending on cartilage type. Specific content affects material properties
• Chondrocytes

  • Nutrients diffuse through the extracellular gel to the chondrocytes
  • Low metabolic activity
• In contrast to bone, cartilage is a much more inert material in your body
• Hyaline cartilage

  • Primarily Type 2 collagen
  • Forms the majority of the unmineralized embryonic cartilage skeleton in vertebrates
  • Pre-ossification templates for endochondral bone

  
• Hyaline cartilage

  • Glassy appearance
  • Retains substantial elasticity
  • Often described as 'rubbery'
  • Articular cartilage specifically refers to hyaline cartilage capping joint articulations
• Decreasing collagen content with depth

  Paralleled by increasing proteoglycan (aggrecan) content
• Higher proteoglycan content


  Leads to increased stiffness of the cartilage
• Osteoarthritis shows worn articular cartilages on the femoral condyles and the associated articulations on the tibia

  
• Fibrocartilage

  • Primarily Type 1 collagen
  • The only cartilage with Type 1 collagen
• Fibrocartilage

  • Tends to be found in areas that are subject to warping or tensile stresses
  • Intervertebral discs; menisci in joints; pubic symphysis, sacroiliac joint
  • Springy & flexible
• Elastic cartilage

  • Also 'yellow cartilage'
  • Similar in histology to hyaline cartilage but the ECM is permeated with elastic fibers (fibrilin and elastin)
• Elastic cartilage

  • Springy & flexible
  • Internal supports for ear; larynx; epiglottis
• Lampreys have a temporary cartilage in ammocoete (larval lamprey) heads with 'fibroblasts' throughout the extracellular matrix containing elastic-like microfibrils
• Adult lamprey cartilage includes 'lamprin' – a protein resembling elastin (think yellow cartilage) in gnathostomes
• The absence of bone ossification is the base condition for Vertebrata

  
• We see skeletons composed of cartilage in many early groups in the fossil record, and in some living groups like lamprey and hagfish today

  
• There are two major living groups of jawed vertebrates: Chondrichthyes (cartilaginous fishes: sharks, rays, and chimaeras) and Osteichthyes (bony fishes: lobe-finned and ray-finned)
• Elastic fibers


  • Fibrilin and elastin
• Elastin


  Can have a yellowish appearance in macroscopic sample, hence the alternate name 'yellow cartilage'
• Elastic cartilage


  Also called 'yellow cartilage'
• Elastic cartilage in ammocoete (larval lamprey) heads


  • A temporary cartilage with 'fibroblasts' throughout the extracellular matrix containing elastic-like microfibrils
• Lamprin


  A protein in adult lamprey cartilage resembling elastin (think yellow cartilage) in gnathostomes
• Skeletons composed of cartilage are seen in many early groups in the fossil record and in some living groups like lamprey and hagfish today

  
• Major living groups of jawed vertebrates


  • Chondrichthyes (cartilaginous fishes: sharks, rays, and chimaeras)
  • Osteichthyes (bony fishes: lobe-finned and ray finned fishes)
• Sharks lack a bony skeleton because they retain some sort of primitive condition
• Bone is a derived feature of the "bony fish"

  
• Fossil jawless vertebrates had copious amounts of bone

  
• Sharks have secondarily LOST their bony skeletons
• Fossil jawed vertebrates also had large amounts of bone
• The absence of bone, and the cartilage-based skeletons of sharks, rays and chimaeroids is a specialized condition