Cartilage Objectives

1.  All three types of cartilage have some common characteristics. Chondrocytes are the main fixed cell in all three types of cartilage. They are large round cells that are randomly scattered through out the tissue. There is a large area of Extracellular matrix surrounding each cell. This ECM is AVASCULAR unlike bone, which is highly vascularized. All cartilage tissue is surrounded by a perichondrium. The difference between the three forms of cartilage lies in the most prevalent extracellular fiber. Hyaline Cartilage is characterized by predominantly Type II Collagen (Car-two-lage), which does not form fibrils with periodicity like its cousin, Type I collagen. Elastic Cartilage is predominantly formed with Elastic fibers. These must be visualized with a special stain (silver stain) to visualize the elastic fibers. Type II Collagen is also present, but not a much as elastic fibers. Elastic cartilage will appear like hyaline if not specially stained. Fibrocartilage is predominated by Type I collagen bundles. It will appear as if it is dense regular connective tissue, but the nuclei will be large and round.

2.  Common Locations for Each Type

  1. Hyaline Cartilage is found in the costal cartilage, the trachea and bronchi (cartilaginous rings surrounding), larynx, nasal cartilage, the articular cartilage of the synovial joints is a specialized hyaline cartilage, and the fetal skeleton
  2. Elastic cartilage is found anywhere resilient support is needed, but elasticity and flexibility are also needed as in the pinna of the ear and the epiglottis
  3. Fibrocartilage is found where toughness and resistance is necessary but give is also needed. Three common locations are the pubic symphysis, the intervertebral discs, and junctions between bone and tendons

3.  Cartilage develops when mesenchymal cells condense to form procartilage. The procartilage will secrete a cartilage matrix.

4.  Integrate the characteristics of individual components of CT to the structure and function of Cartilage

5.  Morphology fits function for the three types of cartilage. Hyaline cartilage is used as a lubricant and as such is high in proteoglycans and glycoproteins. These compounds attract water and therefore support against shock and compression. Elastic cartilage is used to have rigid support but a need for elasticity as in the pinna. For this reason, elastic cartilage has a lot of elastic fiber. Fibrocartilage is used to cushion and absorb impact. It must be rigid so it is full of Type I collagen.

6.  List and describe how the three are classified based on prominent fiber

  1. Hyaline Cartilage is composed mainly of Type II Collagen
  2. Elastic Cartilages is predominantly Elastic Fibers
  3. Fibrocartilage is predominantly Type I Collagen Fibers

7.  The perichondrium is the layer of tissue around the periphery of the cartilaginous tissue. It is divided into two layers, the fibrous layer and the chondrogenic layer. The fibrous layer is dense irregular connective tissue and contains all the blood vessels that provide the nutrients for cartilage. The chondrogenic layers is composed of cells from the fibrous layer that differentiate into chondroblasts that begin to secret extracellular matrix

8.  Ground substance is amorphous; meaning is has no distinct shape. It is quite abundant in cartilage tissue and it is chock full of proteoglycans and glycoproteins. The proteoglycans present are predominantly chondroitin 4/6 sufate and karatan sulfate in the form of aggrecan. This aggrecan molecules form aggregates and are arranged around a hyaluronic acid core. The aggrecan aggregates give the cartilage the gel like consistency. The glycoproteins are chondronectin and chondrocalcin. Chondronectcin is integral in adhering the cell membranes to the extracellular matrix and chondrocalcin is responsible for calcium binding in the ECM

9.  Proteoglycans are arranged in aggrecan aggregates that hold a large amount of water (close to 80% in Hyaline Cartilage is water). They allow diffusion of nutrients and resist compression by diffusing the force.

10.  Articular cartilage is without perichondrium. This allows for direct matrix to matrix contact which is quite slippery.

11.  Articular Cartilage does no have a perichondrium and therefore moves against other articular cartilages quite well. There are large Type II collagen fibers that are arched that run radially to help resist shearing forces. There is a layer of calcified cartilage away from the articular surface to help provide support.

12.  Appositional Growth and Interstitial Growth

  1. Appositional Growth is growth on the surface of tissue. This occurs in the perichondrium in cartilage.
  2. Interstitial Growth is growth from within. This is caused by cell division of chondroblasts already imbedded in a matrix.

13.  Cartilage can usually regenerate it self by appositional growth at the perichondrium, however articular cartilage cannot repair itself because of the lack of nutrient supply. To regrow joint cartilage, holes must be punched through the subchondral bone to allow chondroprogenitor cells to arise from the marrow and migrate into the hole. The chondroprogenitor cells rarely produce hyaline cartilage, but rather more often produce Fibrocartilage.

14.  Classification of joints

  1. Structurally
  2. Fibrous
  3. Sutures
  4. Syndesmoses
  5. gomphoses
  6. Cartilaginous
  7. Synchondroses
  8. Symphysis
  9. Synovial
  10. Synovial fluid, cavity, membrane
  11. Articular capsule, cartilage
  12. Functionally
  13. Synathroses
  14. Amphiarthroses
  15. Diathroses

15.  Describe changes in joint in osteo and rheumatoid arthritis

  1. Rheumatoid Arthritis
  2. Inflamatory
  3. Autoimmune against synovial membrane primarily
  4. Synovial membrane thickens and increase secretion of synovial fluid.
  5. Pannus forms across cartilage and erodes cartilage to the bone allowing them to eventually fuse.
  6. Osteoarthritis
  7. Non Inflammatory
  8. Progressive
  9. Fibrillization of articular cartilage
  10. Proliferation of peripheral cartilage
  11. Replacement of cartilage spurs with boney tissue (hence osteo)