Cartilage And Bone Flashcards
Cartilage
.CT characterized by cells embedded in highly specialized ECM
. Found at sites requiring firm but flexible support
Adult distribution of cartilage in body
. Movable joints
. Immovable joints
. Support of structures
. Vertebral column
Cartilage role in skeletal development
Model for the development of the majority of bones and provides mechanism by which bones grow in length
T/F cartilage is avascular w/ no nerves
T
Composition of cartilage ECM
. Collagen type II (40% dry weight) . Aggrecan . Hyaluronic acid polymers bind to proteoglycans noncovalently via link proteins (bundles bind to II collagen fibrils) . Chondronectin . Water (60-80% fresh hyaline weight)
Aggrecan
250 kD proteoglycan with side chains of chondroitin sulfate and keratin sulfate
Chondronectin
Structural glycoprotein with multiple binding sites
Mechanical properties (compressible and resilient) are cartilage are due to ___
. Presence of fibers
. Amt of anionic charge (amt of sulfate glycosaminoglycans attached to core protein)
. Amount of hydration
Chondroblast
Proliferating undifferentiated cell that begins to synthesize ECM elements
Chondrocyte
. Fully differentiated ECM-forming cells w/ reduced mitotic activity
. Embedded in ECM
Lacunae
Spaces of ECM occupied by chondrocytes
isogenous units (groups)
Groups of chondrocytes derived from same cell
Perichondrium
. CT surrounding cartilage
. Outer fibrous layer (fibroblasts, collagen II)
. Inner cellular layer (undifferentiated condrogenic precursors and chondroblasts
Perichondrium function
. Supporting tissue containing blood vessels, nerves, and lymphatics
. Inner cells participate in repair and appositional growth of cartilage
Cartilage formation steps
. Differentiation of mesenchymal cells
. Cartilage-specific collagen types, elastin, and aggrecan synthesis
. Mature matrix formation
. Accumulation of ECM (territorial and inter territorial matrix)
What occurs in mature matrix formation
. Bound water facilitates diffusion of nutrients and oxygen to cells of cartilage and confers gel-like property to the matrix
Mechanisms of cartilage growth
. Appositional: growth by cell addition to the periphery of the tissue
. interstitial: growth by division of cells w/in tissue (formation of isogenous groups)
Cartilage repair
. Limited ability to repair after injury
. Formation of repair cartilage from perichondrium (matrix of repair cartilage mixed properties of hyaline and fibrocartilage)
Hyaline cartilage
. Type II collagen
. Most common, highly hydrated matrix
. Temporary skeleton during embryonic development
. Forms epiphyseal plates until majority bone growth is done
Elastic cartilage
Type II collagen and elastin
Fibrocartilage
Type I and II collagen
Articulate cartilage
. Covers articulating bones in synovial joints
. Hyaline
Articulate cartilage deep lesion
. Bone region reached, local bleeding can occur spontaneously repairing lesion but turning cartilage from hyaline to fibrocartilage of scar tissue
What occurs in arthritis
. cartilage ECM is degraded
. Articulate surface is lost
Chondrosarcoma
Malignant tumor derived from cartilage cells
Osteosarcoma
Malignant tumor derived from osteoblasts
Bone
. rigid CT w/ limited flexibility
. ECM has Ca and P
T/F Bone is avascular
F, it is highly vascular
Bone features
. Metabolically active
. Ca and P reservoir (99% Ca in body)
. undergoes remodeling (turnover)
How is bone formation and remodeling controlled?
Local paracrine regulators (bone morphogenic proteins and fibroblast growth factor) and hormones in bloodstream (growth hormone, thyroid hormone, estrogen), diet and muscle activity
Osteoblasts
. Bone forming cells
. Produce osteoid
. Control bone matrix mineralization
. Located on bone surfaces (endosteum and periosteum)
Osteoid
Collagen 1 (90% osteoid) Proteoglycans
Osteocalcin
Stimulated by vitamin D, required for bone mineralization
Parathyroid hormone (PTH) in bone
. Activates synthesis of factors in osteoclasts differentiation (macrophage colony-stimulating factor M-CSF, and RANKL
Osteocytes
. Mature bone cells (osteoblasts trapped in Matrix)
. Inactive (has PTH receptors for osteolysis of perilaunar bone)
. No cell division
. Detect mechanical stress on bone
>maintain bone matrix
Osteoclasts
. Bone resorbing cells
. Multinucleted giant cells derived from monocytes
. Located at bone resorption sites
. PTH stimulates them when released from low Ca blood levels
. Calcitonin receptors dec. activity to dec. Ca blood levels
. HaveRANK receptors for RANKL
Osteoblast origin
Mesenchymal stem cells
Mesenchymal stem cells give rise to what cells?
Osteoprogenitor cells, adipocytes, fibroblasts, and myoblasts
Osteoclasts origin
. Mononueclear hemopoietic progenitor cells
.differentiation stimulated by factors produced by osteoblasts
. Osteoclasts undergo apoptotic death when bone resorption is completed
Bone matrix
. Organic matter (35-50% dry weight) embedded in calcified inorganic matrix (50-65% weight)
. Type I collagen, proteoglycans, bone proteins
. Ca hydroxyapatite (major inorganic), Mg, K, Na, Na2CO4, and citrate
What are the bone specific proteins?
Osteocalcin, osteopontin, and osteonectin
What does Ca hydroxyapatite do?
. Association w/ collagen makes bone hard and resistant
. Makes bone Ca reservoir
How does mineralization of bone matrix occur?
. Osteoblasts synthesize organic parts and control mineralization
. Vit. D3 regulates levels of osteocalcin that binds to hydroxyapatite
Ectopic mineralization
. Formation of hydroxyapatite in osteoid-like ECM outside of bone
. Occur in muscle pathologies (myositis ossificans)
Bone resorption
. Carbonic anhydride II in osteoclasts produces carbonic acid
. H ions from acid transported via ruffled border to ECM between osteoclasts and bone
. Acid causes bone decalcification and Ca enters blood stream
. Degradation of organic matrix components via hydrolytic enzymes
Matrix metalloproteinases
Hydrolytic proteins that degrade organic matrix components in bone resorption
What regulates osteoclasts activity?
Calcitonin, Vit. D3, regulatory molecules made by osteoblasts
T/F Maturation of osteoclasts doesn’t always occur in contact with bone
F, it always needs contact of bone
Woven bone
. Primary bone tissue
. Immature, initially formed tissue
. Irregular arrangement of type I fibers
Laminar bone
. Mature bone tissue
. Regularly arranged types I fibers forming lamellar
Cortical bone
. Compact
. 80% total bone mass
. Made up of osteons (Haversian systems) surrounding Haversian canal
Osteon
Parallel bony columns with concentric bony lamellae
Haversian canal
Central canal containing blood vessels, lymph, and nerves
Cancellous/trabecular bone bone
. Spongy bone
. Interconnected trabeculae (honeycomb)
. Forms interior of bones, end of long bones adjacent to bone marrow cavity
. Prominent in vertebrae, carpal, and hip bones
Woven bone remodeling to lamellar bone
. Osteoclasts remove bone matrix and osteoblasts lay down lamellae of bone gradually forming osteons
How are osteons oriented?
In the line of stress exerted on bone
. Parallel to longitudinal axis in long bone
How do osteocytes communicate??
. Cell extensions in canaliculi (small channels)
. No cellular communication between adjacent osteons
Volkmann’s canals
. Canals for vascular connections that anastomose w/ vessels in bone marrow and periosteum
Internal remodeling of bone
. Osteon undergoes cyclic remodeling from central canal outward (centrifugal direction) followed by lamellar formation (centripetal direction
. Central canal never closes
Interstitial lamellae
Remnants of previous lamellae
How are inner and outer surfaces of compact bone organized?
Inner and outer circumferential lamellae
Regional anatomy of long bone
. Epiphysis: end of long bone w/ epiphyseal growth plate
. Metaphysis: neck of bone
. Diaphysis: shaft of long bone w/ compact bone
Flat bones of skull
. 2 layers compact bone plates separated by diploe
Diploe
Spongy bone layer in flat bones of skull
Endosteum
Lines internal surface of bone adjacent to marrow cavity
Ostegenesis imperfecta
Mutations in collagen gene resulting in abnormal collagen production resulting in weak bones
Osteoporosis
. Inc. bone resorption w/o reformation
Primary osteoporosis
. Post-menopausal low estrogen levels
. Type I early postmenopausal: loss of trabeculae bone
. Type II postmenopausal: loss fo trabecular and cortical bone
Secondary osteoporosis
. From disease or medication
. 50% men that have osteoporosis is from this
. Caused by chronic corticosteroid use
Osteomalacia
. Progressive softening and bending of bones
. Defect in mineralization of osteoid from lack of Vit. D or renal tubular dysfunction
Rickets (juvenile osteomalacia)
Defect in mineralization of cartilage in growth plate
Tetracycline
. Antibiotic that can stain teeth
. Binds to Ca in teeth (don’t use when pregnant)
Periosteum
. Inner cellular (osteogenic) layer and outer fibrous layer
. Forms bone during circumferential growth of diaphysis
. Highly vascularized and contains sensory nerves