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75 Cards in this Set
- Front
- Back
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How many types of bones are there?
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-Flat bones(skull,scapula,mandible)
-Long bones(tibia,femur,vertebrae) |
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Name the 2 distinct mechanisms by which bones are formed.
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1.Intramembranous ossification
2.Endochondral ossification |
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What is important about cortical(compact) bones?
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-found on edges
-low surface-to-volume ratio -80 % bone mass -rigid and dense -bone remodelling in cutting cones. |
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Cancellous bones constitutes
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20 % of bone mass.
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Rapid response to calcium stress occurs in cancellous bone.
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True
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What is the site of most bone remodelling?
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Cancellous bone
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Is trabecular bone always changing?
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Yes
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Bone remodelling is responsive to what?
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-Mechanical stress
-Calcium homeostatic stress -regulated by hormones/cytokines |
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Trabecular bone releases Ca2+.
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True
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WHat initiates osteoclasts formation?
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Microfractures
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What happens when bone resorption is > than bone formation?
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Osteoporosis
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What happens when bone formation is > than bone resorption?
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-Osteopetrosis(little bone resorption)
-Osteosclerosis(excess OB + little marrow space) |
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Cutting cone implies
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turnover in cortical bone.
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OC are multinucleate cells that resorb bone.
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True
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Cells have a characteristic
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Ruffled bone
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In OC action, is there a large area for exchange of ions and movement.
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Yes.
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WHat is the purpose of H+ secretion by OC ?
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Acidify and provide correct pH for lysosomal enz. like cathepsin K + digestion of bone.
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What happens to HCO3- during OC action?
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Excreted out of cell.
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Do you have carbonic anhydrase 2 activity?
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Yes.
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OC movement is not essential for bone resorption.
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False.
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Osteopetrosis leads to
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-increased fracture(bone more brittle despite increased density)
-deafness -blindness -anaemia(little bone marrow) |
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What could be one cause of osteopetrosis?
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c-src deficiency
-carbonic anhydrase 2 deficiency is also another cause |
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What happens to OC in osteopetrosis?
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-OC not motile
-integrin-mediated attachment doesnt release ,OC stay attached to bone surface and resorption doesnt proceed normally. |
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What happens during rheumatoid arthritis?
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Joint destruction due to OC action at inappropriate sites.
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Breast cancer metastases to bone cause osteolytic lesions.
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True
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OC are overactive in Pagets disease.
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True
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What happens to some discrete sites in Pagets disease?
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Excess rapid modelling(similar to fracture callus)
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In Pagets disease, some areas have too much bone and others have too little.
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True
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What does tx. of Pagets involve?
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Osteoclast inhibitors-bisphosphonates.
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What are OB ?
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bone forming/mononuclear cells with high capacity for protein production.
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Osteoid matrix is newly formed bone not yet mineralized.
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True
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What are osteocytes?
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Terminally differentiated OB buried within bone.
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Osteocytes constitute
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95 % of cells in adult skeleton.
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How do osteocytes communicate with each other and with OB?
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Via long intercellular processes and gap junctions.
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WHat is the role of mechanosensors?
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Transduce pressure to activate bone remodelling in response to microfractures.
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What are the 2 main extracellular components of bone?
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1. Osteoid(organic matrix)-from OB
2. Mineral salts(hydroxyapatite analogue) |
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Osteoid is made of
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85-90 % type 1 collagen.(also binds and orients other proteins)
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How much NCPs in osteoid?
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10-15 %(albumin,proteoglycans)
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Osteoid provides
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elasticity and structural organization.
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What might NCPs do?
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regulate mineral deposition.
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What are the mineral salts composed of ?
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85 % calcium phosphate
10 % calcium carbonate 1.5 % magnesium phosphate |
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What is the function of mineral salts?
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Confers compressive strength.
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Osteoid makes up 30 % of extracellular matrix.
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True
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Inorganic matrix(minerals) makes up 65 % of bone.
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True
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WHat type of bone is woven bone?
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-disorganized collagen arrangement.
-rapidly laid down. -low Ca2+ content. |
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Woven bone is replaced by
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Lamellar bone.
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What is lamellar bone?
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-Collagen fibres organized in directions of mechanical strains.
-higher calcium density -improved mechanical strength. |
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Collagen fibre content affects
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Ductility
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WHat happens in Osteogenesis imperfecta?
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Impaired bone formation due to heterogenous collagen 1 mutations----> compromised structural integrity of bone matrix and reduced bone mass.
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O. imperfecta leads to
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Increased fracture risk and bone deformities.
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What are the 2 major processes of bone formation?
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1. Secretion of osteoid by OB.
2. Osteoid mineralisation. |
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What controls rate of osteoid mineralisation?
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OB-derived factors
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Mineralisation rate =
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Osteoid deposition rate
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Osteoid matrix accumulates calcium and phosphate.
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True
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What are the initial sites of accumulation of mineralites?
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Holes between collagen fibres
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What happens to the minerals as bone matures?
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Crystals grow in the direction and shape dictated by collagen fibres and NCPs.
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Mineral content and size of crystals can be altered by diet or therapy.(strontium,fluoride)
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True
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What is rickets?
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Dysregulated bone formation due to Vit D/Ca/Phosphorus deficiency----> mineralisation rate NOT equal osteoid deposition rate---> increase fracture risk/bone deformities.
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While balanced,bone cell activity not always equal througout life.
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True(eg. in old age, more resorption than formation)
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How do OB know how much bone needs to be formed?
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Signals such as IGFs from OC communicate with OB.
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Name 2 causes of Osteoporosis in women.
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Age and hormones.
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Name some anti-resorptive therapies to Osteoporosis.
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Calcitonin,Bisphosphonates,Src inhibitors,Androgens----> can prevent further bone loss but not increase BMD.
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PTH treatment increases OB activity in osteoporotic patients.
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True
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Bone remodelling is
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process of bone renewal.
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Bone modelling is
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Growth and reshaping of bones.
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What are the 2 methods of osteogenesis involving replacement of pre-existing CT with bone?
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1. Endochondral ossification-formation of bone within a cartilage model
2. Intramembranous- formation of bone directly on or within fibrous CT membranes. |
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What happens during intramembranous ossif. and where does it occur?
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Growth in width in long bones.
-flat bones of skull -facial bones -clavicles |
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In endochondral ossification,primary ossification centre is in the diaphysis and secondary centre is found in the epiphysis.
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True
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From what does trabecular bone arises from?
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From growth plate
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NAme the diff. parts of the growth plate.
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-Resting zone
-Proliferative zone -Hypertrophic zone -Zone of calcification |
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What determines bone length?
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Chondrocytes proliferation
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What is Laron syndrome?
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Growth hormone receptor mutation.(GH deficiency)----> premature slowing of chondrocyte proliferation(early growth plate closure)
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What are the 3 main stages of fracture repair?
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1. Inflam.-recruitment of mesenchymal cells.
2. Reparation-mesenchyme becomes cartilage & endochon. ossif. begins 3.Bone remodelling with bony callus refined to appropriate shape in response to mechanical forces. |
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What does rigid fixation do?
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Eliminates the cartilage phase(more rapid healing by intramembranous ossif.)
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Bone formation requires balanced osteoid formation and matrix calcification.
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True
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