Histology: Cartilage and Bone Flashcards
Cartilage Characteristics and Functions
-
Avascular (limits the thickness)
- Limited capactiy for repair
- Extensive ECM
- 3 Types:
- Hyaline
- Elastic
- Fibrocartilage
Functions:
- Shock absorbers
- Reduce friction
- Guide development and growth of long bones
Hyaline Cartilage
-
Most common type in body
- Articular surfaces of joints
- Respiratory Tract
- Costal Cartilage
- Appears “glassy” in fresh tissue
-
Chondrocytes (mature cartilage cells)
- Produce and maintain ECM
-
Reside in lacunae
- Isogenous groups (recently divided chondrocytes)
- Composition
- Mostly Water and ECM (NOT cells)
- Type II Collagen
- Aggrecan (proteoglycan)
-
Capsular Matrix (very basophilic, purple) immediately arround chondrocytes –> lots of proteins
- Type VI collagen
- Terrotial Matrix
- Mostyle Type II and IX
- Interstitial Matrix:
- Type II collagen

Elastic Cartilage
Similar structure to hylaine cartilage
- ECM contains lots of elastic fibers (requires fuchsin and orcein stains) in addition to type II collagen
- Covered by Perichondrium
- Found in ear, epiglottis

Fibrocartilage
-
Dense Regular CT and Hyaline Cartilage
-
ECM contains type I and type II collagen
- Chondrocytes in a line
- Also contains fibroblasts (arrows in picture)
-
ECM contains type I and type II collagen
- No perichondrium
- In anulus fibrosus of intervertebral disc
(pubic symphysis and menisci)

Perichondrium
Dense CT covering
- Growth and maintenance of cartilage
- 2 Layers:
- Inner Cellular Layer: mesenchymal stem cells for growth
- Outer Fibrous Layer (type I collagen)

Appositional Cartilage Growth
- Growth at the surface
- Chondroblasts from perichondrium (inner cell layer) deposit matrix
Interstitial Growth
- Growth from within
- Chondrocytes proliferate
- Occurs at epiphysial plate and articular cartilage
- Fibrocartilage can only grow via interstitial growth
Bone Characteristics
- Specialized CT with hard, mineralized matrix
- Functions:
- Support for body
- Bone Marrow (blood cells)
- Ca2+ and Phosphate reservoir
- Two Types:
-
Immature (woven) bone
- First appears in embryonic development
- Temporary - remodeled to mature bone
-
Lower minteral content and more osetocytes
- Appears more basophilic (purple)
-
Mature (lamellar) bone
- Layers
- Higher mineral content (stains more eosinophilic)
- Compact Bone (dense)
- Cancellous Bone (spongy)
-
Immature (woven) bone
Typical Long Bone
Diaphysis
- Long shaft of compact bone with inner marrow cavity
Epiphysis
- Expanded region of end of diaphysis
- Spongy bone within outer shell compact bone
Metaphysis
- Flared region between diaphysis and epiphysis
- Spongy bone with shell of compact bone

Osteon
- Structural and functional unit of compact bone
- Central Canal in center (blood vessels and nerves)
- Cement line: light area covering osteon
-
Lacunae (black dots)
- Contains osteocytes
- Canaliculi extend from lacunae
-
Perforating Canals
- Connect adjacent central canals

Lamellae
Concentric Lamellae
Interstitial Lamellae (osteon remodeled)
Outer Circumferential Lamellae (outside diaphysis)
Inner Circumferential Lamellae (located around marrow cavity)

Cancellous Bone
- Lamellar
- Lacks osteons
- Interconnected Spicules of bone covered by endosteum

Periosteum
Dense Fibrous CT
Covers outer surface of bones
2 Layers:
- Outer fibrous layer
-
Inner cellular layer
- Osteoprogenitor cells
Perforating Fibers
- Collagen fibers the penetrate bone matrix to bind to periosteum

Osteoblasts
Arise from osteoprogenitor cells in periosteum and endostium
- Cuboidal cell layer
- Secrete osteoid (unmineralized bone matrix)
- Lighter pink band in image
- Secrete aklaline phosphatase
- Promotes matrix calcification

Osteocytes
Derived from osteoblasts
- Most abundant bone cell
- In lacunae and extend cytoplasmic processes (canaliculi) into unmineralized matrix to contact adjacent osteocytes
-
Orchestrate bone remodeling
- Signal osteoblasts or osteoclasts
- Increased mechanical stress: more bone
- Decreased mechanical stress: bone loss

Osteoclasts

Large, multinucleated cells
- Derived from monocytes
- requires M-CSF and RANKL
- Involved in resorption and remodeling of bone
- Pump acid (H+ and Cl-) to area being resorbed
- Clear zone demarcates area
- Basolateral side exocytoses digested material

Osteoporosis
Decrease in bone density
- OVERactive osteoclasts, underactive osteoblasts

Osteopetrosis
Abnormally dense bones
- Defective osteoclasts
Bone Matrix
Osteoid (unmineralized matrix)
- Organic component of bone
- Type I collagen
- Osteonectin
- Osteoclacin
Hydroxyapatite Crystals (inorganic component)
- Major calcium reservoir
- Alkaline phosphatase necessary for formation of crystals
Intramembranous Ossification
- Mesenchymal cells aggregate at ossification center
- Differentiate into osteoblasts and secrete osteoid
- Osteoblasts become osteocytes and matrix becomes mineralized
- Bony spicules grow via appositional growth
- Adjacent spicules join to form network of woven immature bone
- Growth and remodeling into mature bone
This process occurs in flat bones of skull
Endochondral Ossification
Forming bone from cartilage model
- Mesenchymal cells aggregate and differentiate into condroblasts to produce cartilage model
- Perichondrial cells give rise to osteoblasts to form bony collar around diaphysis
-
Chondrocytes hypertrophy
- Secrete alkaline phosphatase which calcifies cartilage matrix
- Chondrocytes die
- Blood vessels and osteoprogenitor cells penetrate bone collar
- Differentiate to osteoblasts to secrete osteoid onto calcified cartilage –> mixed spicule
- Osteoclasts remove woven bone and calficied cartilage to form osteon system
Primary Ossification Center
In diaphysis of long bones
Secondary Ossification Center
In epiphysis of long bones
Form after birth
Epiphyseal Plate:
-
Zone of Reserve Cartilage
- Nearest epiphysis
- No proliferation
- Hyaline cartilage
-
Zone of Proliferation
- Chondrocytes proliferate and organize into columns
- Produce collagen and matrix (stains basophilic)
-
Zone of hypertophy
- Chondrocytes enlarge
- Secrete alkaline phosphatase
-
Zone of Calcified Cartilage
- Cartilage matrix becomes calficied
-
Zone of Ossification
- nearest diaphysis
- new bone deposited/cartilage reabsorbed

Fracture Repair
- Blood from torn blood vessels forms hematoma
- Hematoma removed by macrophages and replace dby soft (fibrocartilagenous) callus
- Soft callus invaded by blood vessels with osteoblasts
- Replaced by woven bone to form hard callus
- Woven bone remodeled to form compact and cancellous bone
Synarthroses
Little or no movement
Fibrous Joints:
- Sutures
-
Syndesmosis (between radius and ulna)
- Held together by fibrous tissue
- Gomphosis (teeth)
Cartilagenous Joints:
- Synchondrosis (epiphyseal plates)
-
Symphysis (intervertebral discs)
- Held together by fibrocartilage
Diarthroses
Synovial Joints
- Held together by fibrous capsule of Dense Regular CT
- Filled with synovial fluid
- Synovial Membrane:
- Specialized CT (NOT EPITHELIUM)
-
Type A Synoviocytes
- Macrophage like
-
Type B
- Produce hyaluronan to attract water
-
Articular Cartilage
- Hyaline cartilage NOT covered by perichondrium
- Reduces friction and absorbs shock
Classified by shape/movement