Physiology of Bone

  • Created by: LBCW0502
  • Created on: 24-01-19 14:19
State general features of bone
Strong but light tissue, can be remodelled, can be repaired when broken
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What are the function of bone? (1)
Structural framework (attachment for tendons and ligaments, support for soft tissue). Protect internal organs (e.g. ribs - heart and lungs, skull - brain). Movement (leverage, joints and connections for muscles, length of bone significant/levers)
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What are the function of bone? (2)
Storage depot (minerals e.g. Ca/PO, fats for energy e.g. triglycerides). Haemopoesis (production of erythrocytes and white blood cells)
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Outline the gross structure of bone (1)
Bone marrow surrounded by periosteum. Cancellous/spongy and cortical bone surrounds the blood vessels
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Outline the gross structure of bone (2)
Circular units (osteons - extracellular matrix and osteocytes embedded)
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Describe the chemical composition of bone
Majority is water, followed by organic component (calcium and phosphorous) and inorganic component (collagen, micro-polysaccharides and non-collagenous proteins)
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What are the two types of bone tissue and how do they differ?
Compact bone and spongy bone - they differ in density
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What are the types of canals in cancellous bone?
Volkmann's canal (horizontal canals carry nutrients) and Haversian canal (vertical canals, carry waste products)
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Describe the structure of compact bone (1)
Closely packed osteons (Haversian) systems. Osteon (central canal/osteonic Haversian canal) surrounded by concentric rings (lamellae). Matrix has organic component, protein, collagen (for flexibility), minerals (Ca/PO, hydroxyapatite), 25% water
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Describe the structure of compact bone (2)
Mg/Na bicarbonate. Between matrix rings there spaces (lacunae) and bone cells (osteocytes). Small channels (canaliculi) radiate from lacunae to osteonic canal (passage through hard matrix)
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Describe features of compact bone histology
Layers of bone and osteocytes running around the Haversian canal oblong lacunae (osteocytes are sitting in the lacunae). Canals (canaliculi - interconnect with lacunae with major vessels). Osteocyte nourished and regulated
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Describe features of compact bone (3)
Haversian systems - tightly packed (solid mass). Osteonic canals contain blood vessels parallel to long axis of bone. Blood vessels interconnect via perforating canals with bone surface vessels
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Describe features of cancellous (spongy) bone (1)
Lighter, less dense. Plates (trabeculae) and bars of bone adjacent to small irregular cavities contain red bone marrow. Canaliculi connect to adjacent cavities instead of central Haversian canal
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Describe features of cancellous (spongy) bone (2)
Blood supply appear trabeculae arranged haphazardly but organised - provide maximum strength similar to braces used to support building. Spongy bone trabeculae follow lines of stress, can realign if change direction stress
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Describe features of cancellous (spongy) bone (3)
Well-defined, maximum strengths, follows lines of stress (patient breaks a bone – plastered/needs to be re-aligned correctly (remodelling) and exercise given is within the correct line of stress)
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Describe features of the periosteum
Outside all bone, connective tissue sheath contains inner layers osteogenic cells - osteoblasts - new bone
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Describe features of the endosteum
Inner space lined - osteoblasts and osteoclasts. Osteocytes - layers in adult spongy bone
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Describe features of woven bone
Immature bone. Laid down during fracture repair. Disorganised collagen matrix. Low mineral content softer than mature bone. Replaced by mature compact/cancellous bone (after repair/before differentiating into cancellous spongy bone)
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What are the three types of bone cells? (1)
Osteoblasts (bone forming cells/lay down new bone matrix). Osteocytes (mature bone cells/maintain bone matrix). Osteoclasts (resorb/break down bone). Equilibrium between osteoblasts and osteoclasts maintains bone tissue
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What are the three types of bone cells? (2)
Osteoblasts (lay down new bone matrix - increased by calcitonin, oestrogen, growth hormone). Osteocytes (maintain bone matrix). Osteoclasts (phagocytic cells remove Ca and bone matrix - increased by parathyroid hormone)
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Describe features of osteoprogenitor cells
Mesenchymal stem cells divide to produce osteoblasts. Located in inner cellular layer of periosteum (endosteum). Assist in fracture repair - need to form bone cells after damage
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Describe features of osteoblasts
Line surface of bone. Secrete collagen and organic bone matrix (osteoid) - become calcified soon after deposited when trapped in organic matrix (osteocytes, harden with age)
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Describe features of osteocytes
Sit in calcified matrix in small spaces (lacunae). Osteocyte long processes lie in small channels called canaliculi (transport nutrients/waste). Osteocyte processes contact other osteocytes forming gap junctions (electrical communication)
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Describe features of osteoclasts (1)
In a 'Howship's lacuna' in the endosteum. Large multi-nucleated cells with a ruffled border to resorb bone matrix. Important for remodelling, growth and repair of bone
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Describe features of osteoclasts (2)
Increasing in SA – larger area to reabsorb bone, remove waste products, removal of bone (necrosis)
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Where are osteoclasts derived from? (1)
Not derived from osteoprogenitor cells. Derived from blood monocytes/macrophages (haemopeoitic cells - bone marrow). Precursors released as monocytes into blood collect at sites of bone resorption. Fuse to form multi-nucleated osteoblasts
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Where are osteoclasts derived from? (2)
Stick to surface of bone, break down the bone matrix by secreting acids and enzymes to dissolve the matrix
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Describe features of bone remodelling
Necessary for growth. Mechanical stresses cause release of Ca 2+ to stimulate bone re-modelling. Hormones also control bone re-modelling. Parathyroid hormone stimulates bone resorption. Calcitonin inhibits resorption
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What are the classifications of bone?
Types based on shape (long, short, flat, irregular bones). Types based on development (membranous, cartilaginous, membro-cartilaginous bones). Types based on region (axial, appendicular skeleton, pelvic girdle). Based on structure (compact, spongy)
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What are the types of bones based on shape?
Sutural bones (in between the skull). Irregular bones (vertebrae). Short bones (carpal bones). Flat bones (parietal bone). Long bones (humerus). Sesamoid bones (patella)
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Describe features of long bones
Longer > wide. Long shaft and two bulky ends. Primarily compact bone but may be large amount of spongy bone at ends. E.g. humerus, femur, radius, ulna, tibia and fibula. Miniature long bones e.g. metacarpals, metatarsals, phalanges
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Describe features of short bones
Variety of shapes e.g. cuboid, cuneiform, scaphoid, trapezoid. Primarily spongy bone covered thin layer compact bone e.g. carpal and tarsal bones, wrist and ankle bones
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Describe features of flat bones
Thin, flattened, often curved with two prominent surfaces e.g. scapula, ribs, sternum and most cranium bones ('sandwich' - spongy bone between two layers)
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Describe features of irregular bones
Irregular complex shape, primarily spongy bone covered thin layer compact bone e.g. vertebrae, hip bone and bones in the base of the skull
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Describe general features of bones relating to smooth and rough areas (1)
All bones have surface markings and characteristics (every specific bone, unique). Holes, depressions, smooth facets, lines, projections (passageways). Vessels/nerves. Points of articulation with other bones. Points of attachment (tendon/ligament)
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Describe general features of bones relating to smooth and rough areas (2)
Rough areas – attachment e.g. tendon, muscle. Ligand (points of attachment). Smooth areas – joints (one bone moves around another bone, frictionless for movement). Grooves – blood vessels and nerves located. Genetic component of skeleton
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What are the problems elderly patients face in terms of bone health?
Don’t maintain activity of bones (remodelling without strength), vulnerable to bones breaking when they fall – recommend regular movement, walking/activity
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Describe features of bone matrix maintenance (1)
Factors (activity, body build, gender, race, nutrition, age). Parathyroid (parathormone). Pituitary (growth hormone). Thyroid (calcitonin, -ve effects). Gonads (oestrogen/testosterone). Pancreatic islets (insulin)
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Describe features of bone matrix maintenance (2)
Adrenal cortex (glucocorticosteroid with +/-ve effects, androgens, insulin-like growth hormone)
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Describe features of calcium
99% stored in bone. Constantly being liberated and replaced. Plasma levels are constant (homeostasis). Influences on calcium metabolism
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What is the cause of rickets?
Lack of vitamin D (important for nutrition, enables absorption of calcium)
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Describe features of calcium metabolism (1)
Vitamin D (from diet/synthesised in skin) - Liver (metabolised to 25 hydroxyvitamin D3 - Kidney (activated to 1, 25 hydroxyvitamin D3) - SI (absorption of Ca 2+) and renal tubules (resorption of Ca 2+) - plasma increase of Ca 2+ (bone, utilise Ca 2+)
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Describe features of calcium metabolism (2)
Parathyroid produces parathormone (+ve effect on bone utilisation of Ca 2+). Thyroid produces calcitonin (-ve effect on bone utilisation of Ca 2+)
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Describe features of bone growth (1)
Postnatal bone growth. Length long bones (ossification zone). Rapid division upper cells (chondrocyte columns). Calcification and deterioration (cartilage - column bottom). Subsequent replacement by bone tissue
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Describe features of bone growth (2)
Growth - width, appositional growth - deposition bone matrix by osteoblasts beneath the periosteum
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Describe features of bone growth (3)
< 1 yr (formation of bone collar around hyaline cartilage model). 1-2 yrs (cavitation of hyaline cartilage within cartilage model, invasion of internal cavities by periosteal bud and spongy bone formation)
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Describe features of bone growth (4)
(formation of medullary cavity as ossification continues, appearance of secondary ossification centres in epiphyses - preparation). 15 yrs (ossification of epiphyses, hyaline cartilage remains only in epiphyseal plates/articular cartilage)
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Describe features of an adult bone
Proximal end (spongy bone). Shaft (compact bone). Distal end (marrow cavity)
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Describe features of a child's bone
Epiphysis, diaphysis, epiphyseal plate (growth plate) and epiphysis. Over time, the epiphyseal plate gets smaller. Adult bone - lose growth plate, full bone structure
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Describe features of osteoporotic bone
Bone heavily eroded in places by action of osteoclasts and consists of mainly thin, fragile struts (trabeculae – larger holes)
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Describe the significance of exercise for bone health
Bone can alter strength, stimulate osteoblasts. Mechanical stress increases deposition of mineral salts and increases production of collagen fibres (skeletal muscle pull/gravity). Must be in correct direction force to stimulate correct alignment
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What happens if there is no mechanical stress on bone?
Bone does not remodel normally. Resorption > formation. Immobility - decreases strength, loss of minerals, decrease in collagen fibres
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Describe how ageing relates to bone health (1)
Bone remodelling is constant. In young adults - bone deposition = resorption. Middle age (decrease in bone mass). Osteoclasts (resorption) > osteoblasts (formation)
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Describe how ageing relates to bone health (2)
Loss of bone mass (demineralisation, lose Ca 2+), in >30 yrs female (loss ~ 8%/decade), in >60 yrs male (loss ~3%/decade). Decrease in protein synthesis (decreases - collagen in bone matrix, tensile strength - brittle, fractures)
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Where does the bones own blood supply travel through?
Periosteum to inner bone marrow
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What is hematopoeisis?
Formation of blood cells (produces ~ 500 billion blood cells per day)
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Where is the primary site for hematopoeisis?
Bone marrow. Infants (red marrow - bone cavities - age - replaced - yellow marrow - fat storage). Adults - red marrow only in spongy bone in skull, rubs, sternum, clavicles, vertebrae and pelvis
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What are the functions of red marrow?
Formation of haematocytes (erythrocytes, leucocytes, thrombocytes). Important part of lymphatic system (produces lymphocytes - immune system). Source of mesenchymal stem cells (stromal cells - multipotent) - flow chart diagram
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What are the processes for fracture healing? (1)
Inflammatory, reparative and remodelling. Normal bone - haematoma and granulation tissue - cartilaginous callus - bony callus and cartilaginous remnants - re-modelling - healed fracture
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What are the processes for fracture healing? (2)
Haematoma stage, inflammatory stage, granulation tissue formation, soft callus formation, hard callus formation, remodelling (if there is no callus formation, bone repair cannot take place)
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What does the duration of fracture healing depend on?
Age, health, nutritional status. Faster young > old. Lower limb slower upper spongy bone faster compact
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Give examples of medicines which may cause bone loss
Al containing antacids, phenobarbital, Femara, cancer chemotherapy drugs, cyclosporine A, GnRH, heparin, lithium, Depo-Provera, methotrexate, PPIs, SSRIs, glucocorticosteroids, Tamoxifen, Actos, thyroid hormones in excess
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Describe features of osteoporosis and steroid medicines (1)
Steroid medicines (life saving treatments but can cause bone loss and osteoporosis). Dose of 5 mg, 3 months (increases chance of bone loss/osteoporosis)
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Describe features of osteoporosis and steroid medicines (2)
Steroids important to increase Ca 2+ and vitamin D (+ exercise and no smoking). Prescribed for conditions - RA (not OA), asthma, Crohn's disease, lupus, allergies, inflammation, cancer/autoimmune conditions, organ transplants
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Give examples of common steroid medicines
Cortisone, dexamethasone, methylprednisolone, prednisolone. IV - methylprednisolone sodium succinate
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Other cards in this set

Card 2

Front

What are the function of bone? (1)

Back

Structural framework (attachment for tendons and ligaments, support for soft tissue). Protect internal organs (e.g. ribs - heart and lungs, skull - brain). Movement (leverage, joints and connections for muscles, length of bone significant/levers)

Card 3

Front

What are the function of bone? (2)

Back

Preview of the front of card 3

Card 4

Front

Outline the gross structure of bone (1)

Back

Preview of the front of card 4

Card 5

Front

Outline the gross structure of bone (2)

Back

Preview of the front of card 5
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