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Locomotor year 2 > Bone Metabolism > Flashcards

Bone Metabolism Flashcards

1.Normal bone structure 2.Bone composition -inorganic + organic 3. Stages of bone remodelling 4. Body's Calcium requirements 5. Minerals affecting Calcium metabolism + absorption 5. Process of calium metabolism

1
Q

Name the 2 types of bone

A

Lamellar + Woven

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2
Q

Describe the organisation of lamellar bone?

A

highly organised + layered

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3
Q

What are the two types of lamellar bone?

A

cortical (compact) + cancellous (trabecular)

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4
Q

Describe the structure of compact bone and an example of where it is found?

A

highly organised + multli-layered collagen, dense in different directions
found in diaphysis

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5
Q

Describe the strucutre of trabecular bone and example of where it is found?

A

less organised + fewer layers collagen + larger S.A

found in epiphysis

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6
Q

Which type of bone accounts for the majority of a healthy adult skeleton?

A

compact bone = 80% of total bone mass of an adult

emphasises on healthy- fractures + bone dieseases = woven bone predominates

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7
Q

Which type of bone accounts for the majority of the surface area of the human skeleton and why?

A

Trabecular bone accounts for 10 times the surface area of compact bone. - holey + meshwork of collagen

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8
Q

what type of collagen is predominatly found in bone?

A

collagen type 1

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9
Q

Describe the strucutre and function of woven bone

A

random + sparse collagen organisation =mechanically weak

quickly formed= type of bone laid down initially post fracture

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10
Q

Role of trabeculae bone

A

Tensile strength

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11
Q

Is the composition of bone mainly organic or inorganic?

A

Inorganic - accounts for 60% of bone

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12
Q

What is the main composition of inorganic bone?

A

calcium hypoxyapatite = Ca10(PO4)6(OH)2 (95% of inorganic bone)
(+ water = 5%)

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13
Q

What is the main composition of organic bone?

A

type 1 collagen (90%)

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14
Q

What is the role of the main composition of organic bone?

A

tensile strength

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15
Q

What other 2 factor comprise organic bone and what are their roles?

A

proteoglycans - compressive strength
=-ve charge -atrracts water
growth factors + cytokines + osteoid

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16
Q

In bone remodelling which type of lamellar bone takes longer to be replnished and why?

A

trabeculae bone covers larger S.A

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17
Q

What is the main type of protein found in bone?

A

collagen type 1

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18
Q

What are the 4 types of cells involved in bone remodelling?

A

osteoprogenitor cell + osteoblasts + octeocytes + osteoclasts

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19
Q

Which type of cells involved in bone remodelling are NOT synthesised from the osteoprogenitor cell?

A

osteoclasts - red marrow - haematopoetic lineage

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20
Q

Where are the osteoprogenitor cells found?

A

endosteum + periosteum

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21
Q

Why can MRI scans NOT be used to diagnosis fractures?

A

MRI scans rely on detecting a radio frequency signal emitted by excited hydrogen atoms in the body (present in any tissue containing water molecules) - bone contains very small proportion of water

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22
Q

What are the 4 stages involved in bone remodelling?

A
  1. resting phase
  2. osteoclast reabsorption
  3. osteoblast activity
  4. mineralisation of osteiod
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23
Q

How long does the process of bone remodelling take?

A

3-6 months

24
Q

What the function of the acid released by osteoclasts?

A

HCL - dissolves inorganic bone - calcium hydroxyapatite - Ca + P - Ca leaves bone + enter ISF - increases plasma serum [Ca]

25
Q

What is the function of the main protein digesting enzyme released by osteoclasts?

A

CATHEPSIN K - breaks down collagen type 1

26
Q

What are the 2 substances released by osteoclasts?

A

HCL + Cathespsin K

27
Q

What occurs in osteoblast activity stage of bone remodelling?

A

osteoblasts lay down unmineralised osteoid - immautre bone matrix -fills lacunae formed by ostoclast reabsorption

28
Q

Normal range of serum calcium level

A

2.2-2.6mmol/L (8.5-10.5mg/dL)

29
Q

Recommended daily calcium intake

A

500-1300mg

30
Q

Recommended daily calcium requirement

A

400mg

31
Q

Why does the daily calcium intake exceed requirement

A

calcium is poorly absorbed from gut ( ingest 1000mg - only 400mg will be absorbed)

32
Q

Name the 2 places calcium is excreted

A

kidneys - 200mg (urine)

gut -600-800mg (faeces)

33
Q

What is the balance between calclium intake and excretion?

A

Under normal conditions calcium intake and excretion are EQUAL

34
Q

Name the mineral associated with calcium metabolism

A

phosphate

35
Q

Nomral plasma concentration of Phosphate

A

0.9-1.3mmol/L

36
Q

What is the role of PTH

A

increases [Ca serum]

37
Q

What stimulates PTH synthesis

A

[low Ca serum]

38
Q

What are the 2 ways in which PTH increases serum [Ca]

A
  1. increases Ca reabsorption from kidney

2. increases Ca reabsoption from bone

39
Q

What mineral affects Ca absorption and how?

A

active form of vit D3 ( 1,25(OH)2 vit D3) - increases Ca absorption from GUT

40
Q

What action of PTH indirectly affects Ca absorption?

A

PTH promotes synthesis of active form of vit D3 - increases Ca absorption from gut

41
Q

What organ does PTH act on?

A

kidneys

42
Q

Describe the process by which PTH increases Ca reabsorption from bone

A

PTH - receptor on osteoblasts - activates oesteoblast- produce RANKL - activate RANK receptor on osteoclasts - activate osteoclasts - digest bone - release Ca to ISF

43
Q

2 cells required for osteoclast formation

A

osteoblasts + stromal cells - release RANKL + M-CSF (activation of osteoclast precursor)

44
Q

List RANKL inducers

A

vit D3, PTH, TNF-a, histamine, IGF-1 , PGE2, glucocorticoids, IL 1 , IL11

45
Q

List 2 RANKL inhibitors + their effect on

A

oestrogen + TGF-B = prevent Ca reabsorption from bone - maintains bone

46
Q

What is the consequence of PTH increasing Ca reabsorption from the kidneys?

A

less Ca is excreted in the urine - thus instead more PO4 (phsophate) is excreted

47
Q

What is the action of OPG (osteoprotegrin)?

A

decoy for RANKL- binds to RANKL -inhibits osteoclastogenesis - by inhibiting differentiation of osteoclast precursors + inhibits nuclear kappa B

48
Q

What hormone is released when Ca levels are >2.2.5mmol/L?

A

calcitonin - follicular cells of thyroid gland

49
Q

What are the 2 functions of calcitonin?

A

Decreases Ca serum concentration by:

  1. preventing Ca reabsorption from bone by inhibiting osteoclast differentation + activity
  2. increase Ca excretion from kidney
50
Q

What is the action of vit D3 on Ca absorption?

A

Increases Ca absorption from the gut

51
Q

What are the 2 sources of vit D

A

dairy products + uv light from sun

52
Q

Daily requirement of vit D

A

400IU/daily

53
Q

Action of oestrogen in calcium + bone metabolism

A
  • increases Ca absorption from gut
  • decreased bone Ca re-absorption -inhibits osteoclasts
  • menopause = Ca reabsorption > intake = decrease bone mass = osteoporosis
54
Q

Action of glucocorticoid in calcium + bone metabolism

A
  • decreases Ca absorption from gut
  • increases bone Ca re-absorption
  • consq chronic treatment = OSTEOPOROSIS
55
Q

Action of thyroxine

A

stimulates both bone formation + reabsorption

Locomotor year 2 (11 decks)

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