Bone Growth, Modelling & Remodelling Flashcards
What is the net effect in bone modelling (during growth)?
(Net bone) formation
Where does modelling occur?
Growing skeletons
What are the effects of bone modelling?
Increases medullary cavity for bone marrow
Shaping of skeleton
Where does remodelling occur?
Adult skeleton
What is the net effect of bone remodelling?
No net change (steady-state)
What does “coupling” mean?
Bone formation only occurs in areas of bone resorption
Why does bone remodelling occur? (4)
Calcium homeostasis - calcium stored in hydroxyapatite; hormonal control
Skeletal homeostasis
Adaptation to mechanical forces
Microfractures
What are the four types of mechanical forces exerted on bone?
Compression (pressing together)
Tension (pulling apart)
Torsion (twisting)
Shear (tearing across)
What are the percentages of trabecular and cortical bone masses?
T = 20%
C = 80%
What are the percentages of trabecular and cortical bone turnover?
T = 80%
C = 20%
In what type of bone does most remodelling occur?
Trabecular
Describe the general process of bone remodelling
- Quiescence - lining cells
- Resorption - osteoclast precursors recruited and activated to become osteoclasts and activated to resorb
- Reversal - osteoclasts die and are removed, mesenchymal stem cells recruited and differentiate into osteoblasts and proliferate
- Matrix synthesis - osteoblasts form osteoid, osteocytes formed
- Mineralisation
Why do reversal lines exist?
During remodelling, new osteoid formed is slightly different to previous osteoid (reversal line = boundary)
What is the term describing the processes of bone remodelling?
Activation-Resorption-Formation (ARF)
What is the BMU?
Basic multicellular unit
Wandering team of cells that remodels bone
Describe bone remodelling in cortical bone
Osteoclasts tunnel through bone matrix
Reversal
Osteoblasts deposit osteoid in waves = concentric layers (to form osteons)
What happens during remodelling in the metaphysis?
Osteoclasts resorb ALVEOLAR bone and cartilage
Some cartilage left for scaffolding for lamellar bone
Give two examples of systemic hormones that can affect bone remodelling
Parathyroid hormones
Oestrogen
Calcitonin
Give two examples of growth factors/cytokines that can affect bone remodelling
Bone morphogenetic proteins
Haematopoietic cytokines
Give an example of a (type of) local factor that can affect bone remodelling
Prostaglandins
What four types of substances/structures can affect bone remodelling (systemic to cellular)?
Systemic hormones
Growth factors/cytokines
Local factors
Nuclear transcription factors
In space, what happens to bone and why?
Less load so (2-3%) bone loss (per month)
What commonly occurs in the serving arm of tennis players?
Humeral hypertrophy (~30% increase in bone mass)
What is “billiard’s hand”?
Increased thickness in some finger bones due to mechanical forces from playing billiards
What is Wolff’s law?
(Functional adaptation)
Bone tissue can adapt mass and 3D structure to demands of stress-bearing
How does bone achieve maximal strength with minimal material?
Trabecular bone laid down along lines of maximal compressive/tensile stress
Which cells are the mechanosensors of bone?
Osteocytes
What happens when healing a bone fracture?
Endochondral ossification (bone remembers how to form bone)
Woven bone remodelled to lamellar bone
What is osteoporosis?
Loss of trabecular bone and fatty marrow
What is Paget’s disease of bone?
Too much remodelling results in bone weakening
What would you see in a sample of bone with Paget’s disease?
Lots of reversal lines
How does breast cancer affect bones?
Causes increased resorption
How does prostate cancer affect bones?
Anabolic metastases by turning on osteoblasts
What is osteopetrosis?
Osteoclast defect causing decreased resorption
Less marrow space; cartilage present in secondary spongiosa
What is chondrodysplasia?
Disorganisation of the layers in the epiphyseal plate
