Lecture 6: Cartilage, Bone, and Synovial Joints Flashcards
Cartilage composition
60-80% water, 15% collagens, 9% proteoglycans, 5% multiadhesive glycoproteins, 3-5% cells (mostly chondrocytes)
Functions of cartilage
-Semi-rigid, flexible but sturdy
-Compression resilient/shock absorbing (due to fluid)
-Avascular, no nerves
-Supportive
-Articular surface for joints
-Bone development forerunner
Types of cartilage
- Hyaline (“glassy”)
- Articular (joints)
- Fetal
- Elastic (elastin fibers)
- Fibrocartilage (Type 1 collagen)
Hyaline cartilage
“Default” cartilage. Primarily Type II collagen, glassy appearance due to same refraction between fibers and ground substance. Calcifies with age and has a perichondrium. Chondrocytes in isogenous groups with TM and IM.
Elastic cartilage
Hyaline cartilage with added elastin fibers for extra flexibility. Has a perichondrium. Chondrocytes arranged in singlets.
Fibrocartilage
Hyaline cartilage + added Type I collagen fibers. Less hydrated and stiffer, no perichondrium. Contains fibroblasts and sometimes columns of chondrocytes. Type I collagen fibers anchor into cartilage and connect with other CT.
Fetal cartilage
Early, developing cartilage. During chondrogenesis, mesenchyme condenses and differentiates central chondroblasts as cartilage matrix develops outwards. Superficial mesenchyme later becomes the perichondrion, with nearby cells retaining potency.
Perichondrium
Dense sheet-like CT that encloses hyaline and elastic cartilage compartments. Vascularized; provides nutrient supply for cartilage as nutrients diffuse through the fluid ground substance.
Chondrocytes
Mature chondroblasts that become trapped in lacunae in the matrix. Gather in isogenous groups (due to mitotic division). Primarily glycolytic with large, prominent Golgi and abundant RER (basophilic cytoplasm)
Chondroblasts
Chondrocyte precursors; squamous cells found near the perichondrium/margins. Divide and produce additional cartilage matrix
Territorial matrix (TM)
Cartilage matrix immediately surrounding cells; richer in ground substance and stains more basophilic due to this higher proteoglycan concentration.
Interterritorial matrix (IM)
Cartilage matrix further from chondrocytes; richer in Type II collagen and thus stains lighter than TM.
Capsular matrix
Not visible in LM. Region immediately around lacunae, very rich in Type VI collagen.
Regions of the perichondrium
-Outer fibrous region (more dense sheet like CT)
-Inner chondrogenic region (more cellular; contains chondroblasts)
Types of cartilage growth
- Appositional growth
- Interstitial growth
Appositional growth
Form of growth where new cartilage/bone is laid on an existing cartilage/bone surface. Occurs with differentiation of progenitor cells near the perichondrium/periosteum
Interstitial growth
Form of growth where new tissue is formed within existing tissue (bone/cartilage). Often comes with mitotic division of enclosed cells
How does damage affect cartilage? How does cartilage repair itself?
Cartilage has poor regenerative ability due to its slow metabolism and avascular nature. Perichondrial chondroblasts offer limited differential regeneration, perichondrial fibroblasts can generate scar tissue. Generally, injury can cause bone to replace cartilage and results in less resilient cartilage.
Sections of a long bone
Diaphysis: shaft, contains marrow cavity
Epiphysis: ends, often capped by articular cartilage
Metaphysis: connecting neck, area of growth plate