LECTURE OUTLINE & REVIEW QUESTIONS LECTURE OUTLINE: CARTILAGE Cartilage is a supporting-type connective tissue. Compostion: matrix (intercellular or extracellular materials) cartilage cells (chondroblasts / chondrocytes) A. Cartilage Matrix Protein fibers Collagenous (collagen types 1 or 2) Basic structure of collagen: 3 polypeptide chains  tropocollagen Tropocollagen molecules  collagen fibrils Collagen fibrils  collagen fibers Collagen fibers  collagen fiber bundles Elastic Elastin + microfibrils of fibrillin Ground Substance Proteoglycans: glycosaminoglycans (GAGS) attached to protein core. GAGS attract most water molecules in matrix. Cartilage GAGS: chondroitin 4-sulfate, chondroitin 6- sulfates, keratin sulfate. Proteoglycan Aggregates: proteoglycans (~200) linked to hyaluronic acid. Aggregates form linkages with collagen fibrils Chondronectin: Links collagen fibrils to proteins in cell membranes of cartilage cells. Matrix composition results in cartilage being firm, yielding, resilient B. Cartilage Cells Origin: Mesenchymal cells  chondroblasts Chondroblasts Actively synthesizing and secreting matrix components: protein fibrils / fibers, GAGS, proteoglycan aggregates, chondronectin, hyaluronic acid, etc. Chondrocytes Once surrounded by matrix, chondroblasts decrease their metabolic and secretory activity. Now called chondrocytes. Occupy spaces in matrix called lacunae (sing. = lacuna) Territorial matrix: matrix closest to cell; high in GAGS, low in collagen fibrils; dark staining in LM Interterritorial matrix: farther from cell; lower in GAGS; higher in collagen fibrils; lighter staining in LM Chondroblast / Chondrocyte Comparison Chondroblasts Increased metabolic rate & secretory activity Cytological characteristics: Protein synthesis & secretion Well developed golgi, ger, nucleolus Nucleus light staining (euchromatic): protein gene transcription Cell shape: ovoid Cell surrounded by prominent territorial matrix Chondroccytes Decreased metabolic rate & secretory activity Cytological characteristics: Less prominent golgi, ger, nucleolus Nucleus darker staining: less protein gene transcription Cell shape: round Cell not surrounded by prominent territorial matrix LECTURE OUTLINE & REVIEW QUESTIONS C. Perichondrium Connective tissue covering external surfaces of cartilage Two layers: Outer or Fibrous: Mostly collagenous fibers + some CT cells Inner, Cellular, or Chondrogenic: Fewer collagenous fibers + more CT cells + mesenchymal cells that can differentiate to chondroblasts D. Cartilage is cheap to maintain, but difficult to repair. Avascular: No blood vessels. Nutrients diffuse from blood vessels in pericohondrium or surrounding tissues through matrix to cells. Matrix dense, diffusion slow. Chondrocytes have low metabolic rate. Joint cartilages supplied by synovial fluid. No nerves. E. Cartilage Growth Interstitial Chondroblasts divide mitotically  isogenous groups (cell nests): two or more cartilage cells in one lacuna  cartilage cells produce new matrix  new matrix pushes cells apart & cartilage mass expands. Appositional Mesenchymal cells in perichondrium convert to chondroblasts  Chondroblasts lay down new layer of matrix on outer surfaces of original cartilage mass. F. Cartilage Classification Hyaline (“glassy”) cartilage Most common type of cartilage. Gross appearance: bluish-white, smooth Surfaces covered with perichondrium Matrix packed with collagenous fibrils. (Fibrils not visible in routine LM preparations. Same refractive index as ground substance.) Elastic cartilage Gross appearance: yellowish, smooth Surfaces covered with perichondrium Matrix packed with elastic fibers. Visible only with special stains. Fibrocartilage Transitional from dense ct to hyaline cartilage. No perichondrium. Matrix contains bundles of collagenous fibers. Cartilage cells forced into rows between collagenous bundles. REVIEW QUESTIONS 1. Cartilage is a type of _?_ . (a) epithelial tissue (b) supporting connective tissue (c) connective tissue proper (d) muscle tissue (e) bone tissue 2. The extracellular material of cartilage is called _?_. (a) parenchyma (b) perichondrium (c) matrix (d) stroma (e) interstitial tissue 3. Which of the following is not a component of cartilage matrix ? (a) collagen or elastic fibers (b) proteoglycans such as chondroitin sulfates (c) solvated water molecules (d) osteoid (e) chondronectin 4. Cartilage matrix is produced by _?_. (a) chondroblasts (b) lipoblasts (c) osteoblasts (d) myoblasts (e) fibroblasts 5. Cartilage cells differentiate from _?_. (a) mesenchymal cells (b) fibroblasts (c) monocytes (d) melanocytes (e) keratinocytes 6. Cartilage cells occupy spaces in the cartilage matrix called _?_. (a) alveoli (b) cisternae (c) lacunae (d) fossae (e) sinuses 7. Cartilage cells synthesize and secrete the _?_ that make up the cartilage matrix. (a) glycosaminoglycans (b) chondronectin and the core proteins of proteoglycans (c) collagen and elastic fibers (d) all of these (e) none of these 8. Compared to chondroblasts, chondrocytes _?_. (a) are older (b) are less active metabolically (c) produce fewer secretory materials (d) all of these (e) none of these 9. Compared to chondrocytes, chondroblasts are more likely to have _?_. (a) an extensive g.e.r. (b) a well-developed Golgi apparatus (c) a prominent nucleolus and extensive euchromatin (d) all of these (e) none of these 10. The most common type of cartilage in the human body is _?_. 16. The cartilages covering synovial joint surfaces are _?_. (a) hyaline cartilage (b) are not covered with perichondrium (c) are supplied with nutrients by the synovial fluid (d) all of these (e) none of these 17. Cartilage is "cheap" to maintain, but difficult to repair because _?_. (a) its cells are not very active (b) the dense matrix hinders diffusion of materials to and from the cells (c) it is avascular (d) all of these (e) none of these 18. In _?_ cartilage growth, new layers of cartilage are laid down on the surfaces of the older cartilage mass. (a) interstitial (b) appositional (c) prepositional (d) depositional 19. Appositional cartilage growth depends upon chondroblasts derived from _?_. (a) the fibrous layer of perichondrium (b) the cellular layer of perichondrium (c) cell nests (d) isogenous groups (a) hyaline (b) elastic (c) fibrous (d) none of these 11. Macroscopically, _?_ cartilage is bluish-white in color, glassy in appearance, and smooth and firm to the touch. (a) hyaline (b) elastic (c) fibrous 12. In routine light microscopic preparations, the collagenous fibrils in hyaline cartilage _?_ visible. (a) are (b) are not 13. Fibrocartilage is found in _?_. (a) the intervertebral discs (b) the pubic symphysis (c) in areas where dense regular c.t. meets hyaline cartilage (d) all of these (e) none of these. 14. The connective tissue envelope covering the surfaces of hyaline and elastic cartilages is called _?_. (a) periosteum (b) perichondrium (c) perimysium (d) perineum (e) peritoneum 15. Perichondrium _?_. (a) has an inner cellular layer (b) has an outer fibrous layer (c) contains blood vessels that supply the cartilage (d) all of these (e) none of these 20. The presence of cell nests in a mass of cartilage indicates that it is undergoing _?_. (a) degeneration (b) calcification (c) interstitial growth (d) appositional growth (e) replacement by bone 21. Cartilage cell nests _?_. (a) are also called isogenous groups (b) contain two or more chondroblasts (c) disappear as the cells in the nest begin to produce cartilage matrix (d) all of these (e) none of these 22. Cartilage cell nests are also called isogenous groups because the cells are_?_. (a) oval in shape (b) chondroblasts (c) derived by mitosis from one original chondroblast (d) all of these (e) none of these