cartilage

Examples of cartilage in the following topics:

• Cartilage Growth

  • Chondrification is the process by which cartilage is formed from condensed mesenchyme tissue.
  • The division of cells within cartilage occurs very slowly.
  • Therefore, growth in cartilage is usually not based on an increase in size or mass of the cartilage itself.
  • Remodeling of cartilage is predominantly affected by changes and rearrangements of the collagen matrix, which responds to tensile and compressive forces experienced by the cartilage.
  • However, due to the extremely slow growth of cartilage and its avascular properties, regeneration and growth of cartilage post-injury is still very slow.

• Structure, Type, and Location of Cartilage

  • The cartilage fibrous sheath is called the perichondrium.
  • The division of cells within cartilage occurs very slowly, and thus growth in cartilage is usually not based on an increase in size or mass of the cartilage itself.
  • Hyaline cartilage is found on many joint surfaces.
  • Elastic cartilage is histologically similar to hyaline cartilage but contains many yellow elastic fibers lying in a solid matrix.
  • Elastic cartilage has the most ECM; hyaline a middle amount; and fibrous cartilage has the least amount of ECM.

• Development of Joints

  • Articular cartilage is a flexible material found between bones at movable joints.
  • Following the initial chondrification that occurs during embryogenesis, cartilage growth consists mostly of the development of immature cartilage to a more mature state.
  • Cell division within cartilage occurs very slowly, so growth is not based on a mass increase of the cartilage itself.
  • Articular cartilage is maintained by embedded chondrocytes that comprise only 1% of the cartilage volume.
  • Histological image of the hyaline cartilage which coats the articular surfaces of joints.

• Cartilaginous Joints: Synchodroses

  • Cartilaginous joints are connected entirely by cartilage (fibrocartilage or hyaline).
  • Where the connecting medium is hyaline cartilage, a cartilaginous joint is termed a synchondrosis or primary cartilaginous joint.
  • In this example, the rib articulates with the sternum via the costal cartilage.
  • The epiphyseal plate is a hyaline cartilage plate in the metaphysis at each end of a long bone.
  • Section through occipitosphenoid synchondrosis of an infant, including the cartilage, perichrondrium, and periosteum.

• Postnatal Bone Growth

  • The diaphysis and both epiphyses of a long bone are separated by a growing zone of cartilage (the epiphyseal plate).
  • Zone of reserve cartilage: This region is farthest from the marrow cavity and consists of hyaline cartilage that does not actively transform into bone.
  • This acts as a temporary support for the cartilage that would otherwise be weakened due to the breakdown of the lacunae.
  • Pictured is part of a longitudinal section of a rabbit's developing femur, with parts including: a) Flattened cartilage cells; b) Enlarged cartilage cells; c), d) Newly formed bone; e) Osteoblasts; f) Giant cells or osteoclasts; g), h) Shrunken cartilage cells.
  • Differentiate among the zones of development from cartilage to bone in postnatal ossification

• Thoracic Cage: Sternum

  • The sternum or breastbone is a long, flat, bony plate connected to the rib bones via cartilage that forms the anterior section of the rib cage.
  • Located below the manubrium, the gladiolus is the longest portion of the sternum and articulates with the ribs, either directly or indirectly, through the costal cartilage
  • The thin, pointed xiphoid process forms the most inferior region of the sternum to which the costal cartilage and cartilage of the celiac, or solar, plexus attaches.

• Types of Connective Tissue

  • Cartilage is composed of specialized cells called chondroblasts and, unlike other connective tissues, cartilage does not contain blood vessels.
  • Cartilage is classified in three types: 1) elastic cartilage, 2) hyaline cartilage, and 3) fibrocartilage, which differ in the relative amounts of these three main components.
  • This is similar to hyaline cartilage but is more elastic in nature.
  • This is is the most abundant of all cartilage in the body.
  • It is a major part of the embryonic skeleton, the costal cartilages of the ribs, and the cartilage of the nose, trachea, and larynx.

• Torn Cartilage and Arthroscopy

  • The cartilage in the joints of the body generally covers the ends of long bones and facilitates ease of movement, decreasing friction during movement and providing some degree of cushion when high forces are generated within the joint compartment.
  • Arthroscopic procedures can be performed either to evaluate or to treat many orthopedic conditions including torn floating cartilage, torn surface cartilage, ACL reconstruction, and trimming of damaged cartilage.

• Bone Repair

  • The periosteal cells proximal (closest) to the fracture gap develop into chondroblasts that form hyaline cartilage.
  • The fibroblasts within the granulation tissue develop into chondroblasts that also form hyaline cartilage.
  • Eventually, the fracture gap is bridged by the hyaline cartilage and woven bone, restoring some of its original strength.
  • The next phase is the replacement of the hyaline cartilage and woven bone with lamellar bone.
  • Substitution of the woven bone with lamellar bone precedes the substitution of the hyaline cartilage with lamellar bone.

• Trachea

  • At the top of the trachea and bottom of the larynx is the cricoid cartilage, the only complete ring of cartilage in the trachea.
  • The cartilage of the trachea is considered hyaline cartilage: simple, transparent, and made primarily of collagen.
  • The trachealis muscle connects the open ends of the C-shaped rings of cartilage and contracts during coughing, reducing the size of the lumen of the trachea to increase the air flow rate.
  • A cross section of the trachea, showing the hyaline cartilage, mucus glands, and ciliated epithelium.