Histology Flashcards
(38 cards)
Cartilage Fxns
- Durable + resilient, compliant + cushioning
- Facilitate movement at joints
- Flexible support
- Mechanical protection
Cartilage histology
- Solid, non-mineralized ground substance
- Protein fibers vary in type and density
- Cells in lacunae
- Avascular and lacks innervation
- Perichondrium (outer dense CT layer) in some
Chondroblasts
Young chondrocytes
- Located at periphery
- In perichondrium if present
Chondrocytes
Produce ECM
1. In lacunae
Fibroblasts
Contributes to ECM
1. In perichondrium and fibrocartilage
Cartilage ECM
Provides support and protection
1. Protein fibers
A. Type II collagen: Mose prevalent, produced by chondrocytes
B. Elastic fibers: prevalent in elastic cartilage, produced by chondrocytes
C. Type I collagen: only in fibrocartilage, produced by fibroblasts and some chondrocytes
2. Ground substance
A. Aggregate complex: multiple aggrecan monomers (proteoglycans) attached to hyaluronan macromolecule
B. Multiadhesive glycoproteins
Hyaline cartilage
- Most common
- ECM
A. Type II collagen: dec density
B. Aggrecans in ground matrix [(-) charge]
C. Stains basophilic (darkest near lacunae)
Elastic cartilage
- External ears, epiglottis
- Elastic fibers distributed thru ECM
- (-) charge => basophilic staining
Fibrocartilage
- IVD, pubic symphysis, meniscus
- Hyaline cartilage and dense CT
- ECM:
A. Chondrocytes: basophilic stain
B. Fibroblasts/Type I collagen: acidic stain - Axially arranged isogenous groups
Chondrogenesis
- Aggregation of mesenchymal cells (usually mesoderm derived)
- Mitosis and differentiation into chondroblasts
- Production of ECM and isolation of chondrocytes
- Mitosis and formation of isogenous groups
Cartilage growth
Mitotic division chondrocblasts and chondrocytes -> ECM production
- Interstitial: chondrocyte proliferation in cartilage -> isogenous groups
- Appositional: in periphery or deep layer perichondrium if present
Cartilage repair (adults)
1. Limited: A. Avascularity B. Low metabolic rate C. Chondrocyte immobility D. Limited proliferation 2. Damage often replaced w/ scar tissue 3. Damage underlying perichondrium can be repaired w/o tissue loss
Hyaline calcification
CaPO4 crystals accumulate in ECM
- Endochondral bone growth
- Articular cartilage contact bone tissue
- Aging process
Chondroma
Benign tumor in chartilage
Chondrosarcoma
Malignant tumor in cartilage
1. Rarely metastasize because avascularized
Bone fxn:
- Solid support
- Mechanical protection
- Movement via muscles
- Encloses medullary cavities
- Ca2+ and PO4 reservoir
Bone histology
- Solid, mineralized ground substance
- Protein fibers vary in type and density
- Cells in lacunae
- Vascularized and innervated
- Periosteum (outer CT layer) usually present
A. Except epiphysis - Endosteum lines medullary cavity
Periosteum
Well-vascularized and innervated (sensory) outer layer
1. Fibrous layer: outer layer of dense irregular CT
A. Fibroblasts => type I collagen
2. Cellular layer: osteprogenitor cells
A. Well-defined in growing bones
B. Osteoclasts/blasts
3. Perforating (Sharpey) fibers: penetration into underlying tissues
A. Most dense at tendon and ligament attachment sites
Endosteum
Single layer CT lining spongy bone
1. Contains endosteal and osteoprogenitor cells
Bone formation
- Osteoblasts -> osteocalcin + matrix vesicles + collagen + proteoglycans
- Osteocalcin binds Ca2+ and vesicles inc [PO4]
- Hydroxyapatite crystals in vesicles
- Crystals accumulate
A. Embedded in collagen and proteoglycans
Bone resorption
- Osteoclasts -> sealing zone
- H+ pumps -> acidic micro environment (pH 4.5) -> hydrolytic enzymes
A. Hydroxyapatite dissolution
B. Collagen breakdown - Intracellular degradation
A. Byproducts and Ca2+ -> bloodstream
Intramembranous ossification
- Ossification centers in mesenchyme -> osteoprogenitors -> osteoblasts around capillaries
- Osteoblasts -> osteoid matrix -> woven bone -> traps blasts in lacunae
- Osteoblasts -> calcification -> enlargement
- Woven bone remodeled -> lamellar bone
A. External/internal plates compact
B. Cancellous central - Non-ossified mesenchyme -> periosteum and endosteum
Endochondral ossification
- Fetal hyaline cartilage model develops
- Cartilage calcifies and periosteal bone collar around diaphysis
- Primary ossification center in diaphysis
- Secondary ossification centers in epiphyses
- Bone replaces cartilage, except articular cartilage and epiphyseal plates
- Epiphyseal plate ossify -> epiphyseal lines
Longitudinal bone growth
- Zone of reserve cartilage
- Zone of proliferation
A. Growth
B. Active chondroblasts - Zone of hypertrophy: produces ECM
- Zone of calcified cartilage:
A. Chondrocytes die off
B. Calcification - Zone of ossification
A. Woven -> lamellar