Cartilage

• Skeletal connective tissue


  Specialized forms of supporting/connective tissue that make up the skeletal system
• Bone


  • Provides a rigid protective and supporting framework for most of the soft tissue of the body
• Cartilage


  • Provides semi-rigid support in limited sites such as the respiratory tree and external ear
  • Cartilage formation is also a precursor in the processes of bone formation by either the membranous or endochondral ossification processes
• Joints


  • Composite structures which join the bones of the skeleton and permit varying degrees of movement
• Ligaments


  • Robust but flexible bands of collagenous tissue which contribute to the stability of joints
• Tendons


  • Provide strong pliable connections between muscles and their points of insertion into bones
• Cartilage extracellular matrix


  Enriched with glycosaminoglycans and proteoglycans macromolecules that interact with collagen and elastic fibers
• Types of cartilage


  • Hyaline
  • Elastic
  • Fibrocartilage
• Cartilage


  • The firm consistency of the extracellular matrix allows the tissue to bear mechanical stresses without permanent distortion
  • Supports soft tissue
• Cartilage


  • Shock-absorbing and sliding area for joints that facilitates bone movements because it is smooth-surfaced and resilient
  • Essential for the development and growth of long bones both before and after birth
• Chondrocytes


  Cells in cartilage that synthesize and secrete the extracellular matrix, located in matrix cavities called lacunae
• Components of cartilage matrix


  • Collagen
  • Hyaluronic acid
  • Proteoglycans
  • Glycoproteins
• Cartilage has no lymphatic vessels or nerves
• Cartilage growth


  1. Interstitial growth - chondrocytes grow and divide and lay down more matrix inside the existing cartilage

  2. Appositional growth - new surface layers of matrix are added to the pre-existing matrix by new chondroblasts from the perichondrium
• Hyaline cartilage


  • The most common form, with type II collagen as the principal collagen type in the matrix
  • Bluish-white and translucent, serves as a temporary skeleton in the embryo until replaced by bone
• Hyaline cartilage in adults


  • Located in the articular surfaces of movable joints, walls of larger respiratory passages, ventral ends of ribs, and epiphyseal plate
• Elastic cartilage


  Identical to hyaline cartilage but contains abundant fine elastic fibers in addition to collagen type II fibrils, frequently continuous with hyaline cartilage
• Locations of elastic cartilage


  • Auricle of the ear
  • Wall of the external auditory canals
  • Epiglottis
  • Cuneiform cartilage in the larynx
• Fibrocartilage


  A tissue intermediate between dense connective tissue and hyaline cartilage, characterized by a matrix containing a dense network of coarse type I collagen fibers
• Locations of fibrocartilage


  • Intervertebral disks
  • Attachments of certain ligaments to the cartilaginous surface of bones
  • Symphysis pubis
• Fibrocartilage

  • The collagen fibers either form irregular bundles between the groups of chondrocytes or are aligned in a parallel arrangement along the columns of chondrocytes, taking the direction of the pulling forces
  • No identifiable perichondrium
• Fibrocartilage contains chondrocytes, either singly or in isogenous groups, usually arranged in long rows separated by coarse collagen type I, and the matrix is acidophilic
• Differences between the membranous or endochondral ossification processes
• Synchondroses are growth plates where bone grows during childhood.
• Cartilage is avascular (no blood vessels) and aneural (no nerve endings).