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101 Cards in this Set
- Front
- Back
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BONE: |
- specialized CT, whose extracellular matrix is calcified, incarcerating the cells that secreted it |
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pressure applied to the bone leads to... |
resorption |
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tension applied to the bone results in... |
developmnet of new bone |
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bone- reservoir for minerals of the body: |
it stores about 99% of bodys calcium |
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bone contains a central cavity - the marrow cavity, which hoses... |
the bone marrow
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bone is covered on external surface (except at synovial articulations) with... |
PERIOSTEUM |
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PERIOSTEUM layers: |
* outer- dense fibrous CT
* inner- cellular layer containing osteoprogenitoe cells |
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central cavity of bone is lined by... |
ENDOSTEUM |
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ENDOSTEUM: |
- specialized, thin CT, composed of monolayer of osteoprogenitor cells and osteoblasts |
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fibers that constitue bone are primary... |
type I collagen |
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osteoprogenitor cells --> osteoblasts... |
osteoblasts are responsible for secreting the matrix |
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when osteoblasts are surrounded by matrix they become quiescent and are known as... |
osteocytes |
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the space occupied by osteocyte ... |
lacunae |
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fused bone marrow precursors --> osteoclasts... |
- responsible for bone resorption and remodeling |
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BONE MARTIX components: |
* inorganic: 65% - crystals of calcium hydroxyapatite ( composed of calcium and phosphorus)
* organic: 35% - predominant- collagen type I |
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hydroxyapatite crystals Ca10(PO4)6(OH)2 |
- arranged in order fashion along the type I collagen fibers - free surface surrounded by ground substance - the surface ions of crystals attract H2O and form hydration shell - osteocalcin and osteopontin bind to it (glycoproteins) |
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hydration shell function: |
permits ion exchange with the extracellular fluid |
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collagen type I 80-90% of organic bone components: |
- highly cross-linked, which prevents it from being easily extracted |
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stimulates synthesis of bony glycoproteins |
vitamin D |
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protein that permites adhesion of osteoblasts and osteocytes... |
sialoprotein |
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Osteoprogenitor cells: |
- derived from embryonic mesenchymal cells - retain their ability to undergo mitosis - located in inner cellular layer of periosteum, lining Haversian canals in endosteum - may differentiate into chondrogenic cells - most active during period of intense bone growth |
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Osteoblasts: |
- synthesize organic matrix of bone
- posses receptors for parathyroid hormone
- derived from osteoprogenitor cells under influance of bone morphogenic protein BMP family and transforming growth factor-beta
- produce RANKL( receptor for activation of nuclear factor kappa B) , osteocalcin, osteonectin, bone sialoprotein, macrophage colony-stimulating factor M-CSF
- active- basophilic cytoplasm with pink granules
- arrangment- cuboidal to columnar cells
- short processes- gap junctions (fewer than between osteocytes) |
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osteoblasts are rich in enzyme.... during active bone formation it's level also increases in blood |
ALKALINE PHOSPHATASE |
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OSTEOID |
thin substance that separates osteoblasts and osteocytes from calcified matrix (it is uncalcified bone matrix) |
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factors on the osteoblast membrane: |
-integrins- parathyroid hormone receptors, when parathyroid hormone binds to these receprors it stimulates osteoblasts to secrete osteoprotegerin ligand OPGL |
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osteoprotegerin ligand OPGL is a factor that |
- induces differentiation of preosteoclasts into osteoclasts - increases RANKL expression |
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osteoblasts secrete an osteoclast- stimulating factor which... |
activates osteoclasts to resorb bone |
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osteoblasts secrete enzymes responsible for removing osteoid so that... |
osteoclasts can make contact with mineralized bone surface |
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Osteocytes: |
- mature bone cells -derived from osteoblasts that became trapped in their lacunae - processes of osteocytes make gap junctions through which ions and small substances can move between the cells - inactive cells but secrete substances necessary - respond to mechanotransduction, releasing cAMP, osteocalcin, insulin-like growth factor |
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canaliculi: |
- radiating out, in all directions from the lacunaa - narrow, tunnel-like space - house cytoplasmic processes of osteocytes - contain extracellular fluid carring nutrients and metabolites --> osteocytes |
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periosteocytic space- |
- interval between osteocyte plasmalemma and walls of the lacunae and canaliculi - occupied by extracellular fliud - posses extensive network of canaliculi |
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Osteoclasts: |
- multinucleated, large, motile cells
- orginate from granulocyte-macrophage progenitors (mononuclear-phagocyte system)
- play role in bone resorption
- have receptors for: osteoclasts stimulating factor, colony-stimulating factor-1, osteoprotegerin OPG, calcitonin
- acidophilic cytoplasm
- occupy shallow depresion- Howship's lacunae |
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Osteoclasts secrete three signaling molecules: |
- macrophage colony-stimulating factor M-CSF--> binds to receptor on macrophage --> proliferating octeoclast precursor --> expresion and activation of kappa B (RANK) on precursor - RANKL - OPG- member of tumor necrosis factor receptor TNFR, interacting with RANKL prohibiting it from binding to macrophage thus inhibiting osteoclast formation |
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regulate bone matabolism and osteoclast activity: |
RANKL RANK OPG |
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Osteoclast active in bone resorption may be subdivided into four morphologically recognizable regions: |
- basal zone (the farthest from Howship lacunae, houses most organelles)
- ruffled border - projection of the cell directly involved in resorption, finger-like processes project into- subosteoclastic compartment
- clear zone (surrounds periphery of ruffled border), organelle free, contains many actin myofilaments --> actin ring- contact with Howship lacunae
- vesicular zone (between basal zone and ruffled border), consists of many endocytotic, exocytotic vesicles that ferry lysosomal enzymes |
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Mechnism of bone resorption: |
carbonic anhydrase: CO2 + H2O --> H2CO3 dissociation: H+ +HCO3- ( bicarbonate ions and Na+ cross plasmalemma --> capillaries) proton pumps of plasmalemma of ruffled border of the osteoclasts actively transport H+ into subosteocentric compartment lower pH- acidic (Cl- ions follow passively) inorganic component of the matrix dissolves |
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Lysosomal hydrolases Metalloproteinases: collagenase, gelatinase |
are secrteted by osteoclasts into subosteoclastic compartment to degenerate organic components of bone matrix --> broken down into aminoacids, disacharides --> capillaries |
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Osteopetrosis- |
- genetic disorder where osteoclasts do not posses ruffled border! - no bone resorption, increased bone density - anemia decreased marrow space, blindness, cranial nerve involvement |
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Hormonal control of bone resorption: |
parathyroid gland ( chief cells) --> parathyroid hormone --> increase concentration of calcium in the blood, increase bone resorption
thyroid gland (parafollicular cells- C-cells) --> calcitonin --> reduces blood calcium level, decrease osteoclasts activity, stimulates osteoblasts |
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BONE STRUCTURE: (according to the anatomical shape) |
* long (tibia) * short (carpal bones) * flat (skull) * irregular (sphenoid, ethmoid) * sesamoid (patella) |
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BONY STRUCTURE: |
* compact bone- dense, on the outside surface, houses Haversian system
* cancellous (spongy bone) - porous portion lining the marrow cavity, houses irregular lamellae |
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trabeculae and spicules- |
jutting out from the internal surface of the compact bone through spongy bone to bone marrow |
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BONE MARROW: |
- red bone marrow- where blood celld are forming
- yellow bone marrow composed mostly of fat |
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shaft |
trzon |
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shaft of the long bone- |
diaphysis |
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articular ends are called... |
epiphyses |
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in the person who is still growing the diaphysis is separated from epiphysis by... |
epiphyseal plate (of cartilage) |
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top of the articular end of bone: |
- highly polished articular hyaline cartilage |
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the area of transition between epiphysis and diaphysis... |
metaphysis (where columns of spongy bone are localized) - bone grows in length |
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PERIOSTEUM: |
- noncalcified, dense irregular collagenous CT covering the external bone's surface and inserting into in via Sharpey's fibers
- diaphysis is covered by periosteum, except where tendons and muscles insert
- outer fibrous layer, inner cellular layer |
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no periosteum: |
- on surfaces of bone with articular cartilage - absent in sesamoid bones - patella |
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flat bones of skull: |
- two thick layers of compact bone called - inner and outer tables which surround the spongy bone- diploe- sandwitched between them
- outer table posses- periosteum- pericranium - inner table posses- dura mater |
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Bony types based on microscopic observations: |
- primary (immature bone)
- secondary (mature bone) |
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PRIMARY BONE (woven, immature) |
- the first formed during fetal development and bone repair - lesser mineral content than secondary bone, abundant with osteocytes, collagen - organizes secondary bone |
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exceptions where primary (woven) bone does not organizes secondary bone: |
- sutures of calvaria - insertion sites for tendons - bony alveoli surrounding the teeth |
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SECONDARY BONE (lamellar, mature) |
- composed of parallel or concentric bony lamellae - osteocytes, canaliculi with their processes- network of communicating channels - matrix is more calcified |
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lamellae- |
blaszki, płytki |
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Lamellar systems in compact bone: |
- outer circumferential lamellae
- inner circumferential lamellae
- osteons (haversian canal systems)
- interstitial lamellae |
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Outer circumferential lamellae: |
- just deep to th epeiosteum - outer most region of the diaphysis - contain Sharpey's fibers anchoring the peiosteum to the bone |
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Inner circumferential lamellae: |
- not as extensive as outer -encircle the marrow cavity - trabeculae of spongy bone extend from the inner circumferential lamellae into bone marrow cavity |
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Haversian canal systems - Osteons: |
- in compact bone - composed of cylinders of lamellae concentrically arranged around vascular space- haversian canal - bounded by thin cementing line- composed mostly of calcified ground substance with collagen fibers - bifurcate
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Haversian canal: |
- lined by layer of osteoblasts and osteoprogenitor cells, - houses neurovascular bundle with CT
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Haversian canals of adjacent osteons are connected to each other by... |
Volkmann's canals
- vascular spaces that are oriented oblique to or perpendicular to Haversian canals |
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during the formation of osteons the lamella closest to cementing line is ... |
the first to be formed |
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the more lamellae are added the more... |
reduced is the diameter of Haversian canal |
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bone is being remodeled osteoclasts resorb osteons which are replaced by... |
osteoblasts |
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Interstitial lamellea: |
- remnant of osteons - remain as irregular arcs of lamellar fragments - (surrounded by osteons and cementing line) |
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Bone formation: |
- intramembranous
- endochondrial |
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Intramembranous bone formation: |
- occurs withinrich vascularized mesenchymal tissue, whoes cells kake contact with eachother via long processes - mesenchymal cells --> osteoblasts - - bone matrix --> network of spicules and trabeculae *primary ossification center --> calcification --> osteocytes - - systems of canaliculi - continuous activity of mesenchymal cells provides a supply of undifferenciated osteoprogenitor cells - spongy-like network of trabeculae - in most flat bones |
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regions of mesenchymal tissue that remain uncalcified differentiate into... |
periosteum and endosteum |
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spongy bone deep to the periosteum and periosteal layer of dura mater of flat bones are transformed into... |
compact bone forming inner and outer tables |
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Endochondrial bone formation: |
- requires the presence of a cartilage template (szablon) - most of the long and short bones - occurs in phases: * formation of miniature hyaline cartilage model * continuous growth of the model which serves as structural scaffold for bone development (hyper * resorption and replacement by bone |
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Events that occur at the primary center of ossification: |
within the embryo --> hyaline cartilage model of that bone develops --> appositional and interstitial growth --> chondrocytes hypertrophy, glycogen accumulation, , enlargment of lacunae, calcified
perichondrium at the midriff of the diaphysis of cartilage becomes vascularized ! --> chondrogenic cells became osteoprogenitor cells --> osteoblasts, perichondrium--> periosteum
osteoblasts secrete bone matrix, forming subperiosteal bone collar (intramembranous bone formation)
due to collar, chpertrophic chondrocytes die- this process is responsible for presence of empty lacunae, future marrow cavity
periosteal bud (osteogenic bud) : osteoprogenitor cells, hemopoietic cells, blood vessels
osteoprogenitor cells --> osteoblasts- elaborate matrix on surface of calcified cartilage : calcified cartilage/ calcified bone complex
thicker subperiosteal bone, osteoclasts resorption of calcified cartilage/ calcified bone complex --> enlargement of marrow cavities |
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diaphysis is repleaced by bone except... |
epiphyseal plates- reponsible for continuous growth till 20 |
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Events occurring at the secondary centers of ossification: |
- ossification begins at epiphysis (except there is no bone collar) - growth of bone occurs at epiphyseal plate - epiphysis and diaphysis become continuous |
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Continuous lengthening of bone depends on... |
epiphysea plate |
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ZONES at the epiphyseal plate:
(bone growth in length) |
- Zone of reserve (quiescent) cartilage - Zone of proliferating cartilage - Zone of maturation and hyperthrophy ( hypertrophic cartilage) - Zone of calcification ( calcareous cartilage) - Zone of ossification (trabeculae) |
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trabeculae- |
beleczki kostne |
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Bone growth in width: |
- takes place by appositional growth - growth of the diaphysis - osteoprogenitor cells ( in inner periosteum) --> osteoblasts, elaborate matrix in subperiosteal bone surface - bone resorption internally so that marrow space can be enlarged |
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Calcification of bone: |
- begins when there are deposits of calcium phosphate on the collagen fibril - stimulated by osteonectin and bone sialoprotein |
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Bone remodeling: |
- in adult bone development is balanced with bone resorption as bone is remodeled to meet stresses places on it
- Haversian systems are continually being replaced
- Bone must be resorbed from one area and added to another to meet changing stresses placed on it ( weight, posture, fractures) - COUPLING
- calcaneous bone and cortical bone are not remodeled in the same fasion |
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osteoclasts recruided to the area to resorb the bone matrix form... |
absorption cavities |
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osteoclasts that are recruited to the area to resorb bone matrix form... |
absorption cavities |
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Bone repair: |
- involves both intramembranous and endochondrial bone formation
- bone haversians canals are without blood, osteocytes become pyknotic --> lysis
steps:
- formation of the hematoma (hemorrhaging)
- blood clot --> fibroblasts --> granulation tissue
- formation of internal callus
- cartilage --> cancellous bone (endochondrialy) * primary bone
- remodeling primary bone of intramembranous bone formation is replaced by secondary bone
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parathyroid hormone: |
- secreted by chief cells of parathyroid hormone when blood Ca2+ level is below normal
- activating receprors on osteoblasts --> OPGL and osteoclast- stimulating factor |
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calcitonin: |
parafolicular cells (C cells) of thyroid gland
when calcium ion level in blood is elevated
activates receptors on osteoclasts- inhibiting them
osteoblasts --> osteoid Ca2+ deposid increases |
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somatotropin : |
influences bone development via somatomedins (insulin like growth factors) |
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interleukin-1 |
- released by osteoblasts, activates osteoclasts precursors to proliferate * indirect role in osteoclasts stimulation |
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Tumor necrosis factor- |
released by macrophages act in fashion similar to interleukin 1 |
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Colony-stimulating factor-1 |
- released by bone marrow stromal cells, induces osteoclasts formation |
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Interleukin-6 |
- released by various cells especially by osteoclasts, stimulates the formation of other osteoclasts |
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OPG |
- inhibits osteoclasts differentiation |
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Interferon gamma- |
- released by T-lymphocytes, inhibits differentiation of osteoclasts precursors |
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Transforming growth factor-beta |
- liberated from bone matrix during osteoclasia
- induces osteoblasts to manufacture matrix, mineralization
- prevents proliferation of osteoclasts |
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Acromegaly: |
- in adults who produce excessive somatotropin, abnormal increase in bone deposition without resorption |
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OSTEOPOROSIS: |
- when estrogen secretion drops (estrogen normally binds to osteoblast activating them for matrix secretion) |
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estrogen replacement therapy: |
- increases the risk of heart disease, stroke, breast cancer, blood clots |
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RICKETS: |
- disease in infants and children who are deficient in vitamin D - intestinal mucosa cannot absorbe the calcium |
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Osteomalacia: |
- adult rickets, result from prolonged deficiency of vitamin D
- fetus requires calcium |
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Scurvy |
- condition resulting from deficiency of vitamin D - deficient collagen production, reduced formation of bone matrix |
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JOINTS: |
- cells in synovial layer: * type A cells -macrophages * type B cells fibroglasts that secrete synovial fluid (hyaluronic acid and lubricin) |
