Cartilage and Bone Flashcards
Supporting CT
bone and cartilage
cartilage distribution
- nose
- articular cartilage
- costal cartilage
- intervertebral discs
- pubic symphysis
- external ear
- epiglottis
functions of cartilage
- support the soft tissues
- forms articular surfaces of long bones
- growth in length of long bones
Collagen in cart
maintains tissue shape and produces tensile strength
proteoglycan aggregates in cart
provide resilience
molecular organization in cartilage matrix
fiber reenforced gel
-permits cart to bear mechanical stress without permanent distortion
Proteoglycan aggregate synthesis
- protein core and GAGs
- bind proteoglycan to a core of hyaluronic acid with link proteins to make aggregates
principle GAGs in cart
- chondroitin 4-sulfate
- chondriotin 6- sulfate
- Keratan sulfate
Protein secreting cell-chondrocyte
- round diffuse nucleus
- prominent nucleolus
- rich in RER
- well developed Gogli
- enough mitochondria
- synthesizes collagens and other matrix components
ECM
- proteoglycan aggregates
- type II collagen-fibrillar scaffold
Perochondrium
- formed from mesenchyme surrounding center of chondrification
- composed of two layers
- outer, fibrous layer made of type I collagen and fibroblasts
- inner, chondrogenic later made of chondroblasts
Appositional growth
- mitosis of chondroblasts,
- differentiation into chondroctyes, which produce and secrete ECM.
- chondrocytes live in lacunae
- adds new cells and ECM to surface
- persists but latent in adult
Interstitial growth
- growth from within
- chondrocytes are capable of mitosis
- daughter cells produce ECM
- produce clusters of cells called isogenous groups
- diminishes with age
Avascular consequences
- size limitation
- low MR
- poor potential for repair (slow and often incomplete except for children)
- systemic drug treatment is difficult
Types of cartilage
- differ mainly in matrix composition
- hyaline, elastic, fibro cartilage
Hyaline cartilage
- most common, found in ribs, trachea, larynx, bronchi, joints, epiphyseal plate, nose
- fill lacunae
- subjected to degenerative process-calcification
Hyaline cartilage matrix
- proteoglycan aggregates and type II collagen
- basophilic
- capsular matrix around each lacuna that is more basophilic (richer in sulfated GAGs)
- interterritorial matrix is less basophilic
- type II collagen
- produced by chondrocytes
- nutrition of chondrocytes
type II collagen in hyaline ECM
- 10-20 nm diameter fibrils
- lack 64 nm periodicity
Elastic cartilage
- located where flexible support is needed- ear, epiglottis, eustachian tube, larynx
- chondrocytes-same as in hyaline
- less susceptible to degenerative or age related changes
Elastic cartilage matrix
- more flexible than hyaline
- less homogenous in appearance than hyaline
- contains elastic fibers which stain specially with orcein dyes
Fibrocartilage
- annulus fibrosus, pubic symphysis, a few tendons, menisci of the joint
- chondrocytes
Fibrocartilage ECM
- reduced amount of ground substance
- increased amount of collagen, which causes matrix to be eosinophilic
- usually type I collagen
Vertebrae
- nucleus palposus derived from notochord
- end plate made of hyaline cartilage
- annulus fibrosus is fibrocartilage
fibrocartilage vs dense regular CT
- irregular fiber distribution
- fewer cells per unit area
- rounder chondrocytes
Functions of bone
- supports fleshy structures
- protect vital organs
- harbors bone marrow
- reservoir of calcium, phosphate, etc
- movement
similarities between bone and cartilage
- supporting CT
- mostly consists of ECM
- oseocytes reside in lacunae
- surrounded by periosteum-specialzed CT with osteogenic potential
- appositional growth
differences between bone and cartilage
- no interstitial growth in bone
- more regular arrangement of cells and fibers in bone
- bone is vascularized and has nerves
- ECM is normal for calcification
spongy bone
- cancellous, trabecular
- consists of 3D lattice of branching trabeculae
- form system of interconnecting spaces which are filled with bone marrow
compact bone
- more solid in appearance
- spaces only seen under microscope
long bone
- diaphysis- cylindrical part–thick outer layer of compact bone with thin narrow cavity containing spongy bone
- epiphysis- bulbous ends–spongy bone covered by a layer of compact bone
Compact bone micro
A.
- ECM laid down in lamellae
-within each lamella collagen fibers are oriented parallel to one another, but perpendicular to fibers in adjacent lamella-lacunae in concentric patterns in ECM
B.
-lacunae distributed in concentric patterns throughout ECM
-lacuna contains osteocyte which has cytoplasmic processes
-canaliculi radiate out from each lacuna
C.
-has specific lamellar patterns
canaliculi
small channels that radiate in all directions through ECM from each lacuna, connect to adjacent lacunae and open to extracellular fluid
- essential for nutrition of osteocytes
- filopodial processes from osteocytes extend into canaliculi
- processes of adjacent osteocytes make contact with one another via gap junctions
three types of lamellar organization
1.concentric:
haversian canals (osteons)
volkmann canals
- inner and outer circumferential
3-intersitial
haversian canals
-run parallel to long axis of bone and contain small blood vessles, loose CT, and nerves
volkmann canals
- run at oblique angle to the long axis of the bone
- connect haversian canals to each other and to the free surface
outer and inner circumferential lamellae
inner is just beneath endosteum
outer is just underneath periosteum
-consist of a few lamellae that extend around the circumference of the shaft
interstitial lamellae
- angular fragments of lamellar bone (leftover)
- located between Haversian systems
ECM of compact bone-organic
- type I collagen
- non-collagenous proteins
- ground substance-GAGs and proteoglycans (not aggregated)
- toughness and resilience
ECM of compact bone-inorganic
- calcium phosphate (hydroxyapatite)-thin plates or crystals, associated with collagen fibers
- responsible for hardness
outer layer of periosteum
- consists of dense irregular CT
- has a few fibroblasts
- blood vessels which enter volkmans canals
- some of its collagen fibers anchor periosteum to bone
inner layer of periosteum
- has osteogenic potential
- appearance depends on functional state
- osteoblasts present during embryonic and post natal growth
- osteoprogenitor cells in adults
osteoprogenitor cells
- not actively making bone
- low profile
- compact chromatin
- less basophilic cytoplasm
- can be reactivated
endosteum
more delicate single layered structure
- lines surfaces of vascular channels
- covers the tranbeculae of spongy bone
spongy bone
a-3D lattice of branching bony trabeculae
b-interconnecting spaces that are lined with endosteum and filled with bone marrow
c-intercellular substance is lamellar- but not concentric, no BV, no canals-nourished via canaliculi
d-osetocytes are identical to compact- only nuclei visible in H&E, processes extend into canaliculi
Remodeling of bone-functional adaptation
- bone destroyed and replaced as soon as it is formed–whole skeleton once every 10 years.
- occurs in spongy and compact
- relative activity of osteoblasts and osteoclasts
- bone adapts to mechanical load- osteocytes are mechanotransducers of local strain
- remodeling removes microdamage
major functions of functional adaptation
- maximal strength with minimum bone mass
2. removal of microdamage and replacement with new bone
Osteoclasts
- located in small pits on surface of bone-from fusion of monocytes (Howship’s lacunae or resorption bays)
- multinucleated
- eosinophilic in cytoplasm
- ruffled border
- rich in mito and lysosome
- attached to bone with podosomes that form tight seal
- break down organic matrix by means of lysosomal hydrolytic enzymes
- dissolution of bone mineral by creating acid environment
Osteoclasts 2
- cathepsins- hydrolytic enzymes that digest organic matrix
- acid environment created by proton pump solubilized inorganic matrix, and provides optimum pH for hydrolytic enzymes
osteoporosis
- inbalance between osteoclasts and osteoblasts
- osteoclasts may increase when estrogen decreases
- resorption exceeds formation
- skeletal fragility and increased susceptibility to fractures-vertebral common hip debilitating
- treatment with bisphosphonates inhibit osteoclasts but can lead to osteonecrosis and increased risk of femoral fractures
- also common among older men-20% over 50 have hip, spine, or wrist
