Bone Metabolism

Question 1

Name the 2 types of bone

Answer 1

Lamellar + Woven

Question 2

Describe the organisation of lamellar bone?

Answer 2

highly organised + layered

Question 3

What are the two types of lamellar bone?

Answer 3

cortical (compact) + cancellous (trabecular)

Question 4

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

Answer 4

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

Question 5

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

Answer 5

less organised + fewer layers collagen + larger S.A

found in epiphysis

Question 6

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

Answer 6

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

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

Question 7

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

Answer 7

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

Question 8

what type of collagen is predominatly found in bone?

Answer 8

collagen type 1

Question 9

Describe the strucutre and function of woven bone

Answer 9

random + sparse collagen organisation =mechanically weak

quickly formed= type of bone laid down initially post fracture

Question 10

Role of trabeculae bone

Answer 10

Tensile strength

Question 11

Is the composition of bone mainly organic or inorganic?

Answer 11

Inorganic - accounts for 60% of bone

Question 12

What is the main composition of inorganic bone?

Answer 12

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

Question 13

What is the main composition of organic bone?

Answer 13

type 1 collagen (90%)

Question 14

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

Answer 14

tensile strength

Question 15

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

Answer 15

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

Question 16

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

Answer 16

trabeculae bone covers larger S.A

Question 17

What is the main type of protein found in bone?

Answer 17

collagen type 1

Question 18

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

Answer 18

osteoprogenitor cell + osteoblasts + octeocytes + osteoclasts

Question 19

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

Answer 19

osteoclasts - red marrow - haematopoetic lineage

Question 20

Where are the osteoprogenitor cells found?

Answer 20

endosteum + periosteum

Question 21

Why can MRI scans NOT be used to diagnosis fractures?

Answer 21

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

Question 22

What are the 4 stages involved in bone remodelling?

Answer 22

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

Question 23

How long does the process of bone remodelling take?

Answer 23

3-6 months

Question 24

What the function of the acid released by osteoclasts?

Answer 24

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

Question 25

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

Answer 25

CATHEPSIN K - breaks down collagen type 1

Question 26

What are the 2 substances released by osteoclasts?

Answer 26

HCL + Cathespsin K

Question 27

What occurs in osteoblast activity stage of bone remodelling?

Answer 27

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

Question 28

Normal range of serum calcium level

Answer 28

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

Question 29

Recommended daily calcium intake

Answer 29

500-1300mg

Question 30

Recommended daily calcium requirement

Answer 30

400mg

Question 31

Why does the daily calcium intake exceed requirement

Answer 31

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

Question 32

Name the 2 places calcium is excreted

Answer 32

kidneys - 200mg (urine) | gut -600-800mg (faeces)

Question 33

What is the balance between calclium intake and excretion?

Answer 33

Under normal conditions calcium intake and excretion are EQUAL

Question 34

Name the mineral associated with calcium metabolism

Answer 34

phosphate

Question 35

Nomral plasma concentration of Phosphate

Answer 35

0.9-1.3mmol/L

Question 36

What is the role of PTH

Answer 36

increases [Ca serum]

Question 37

What stimulates PTH synthesis

Answer 37

[low Ca serum]

Question 38

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

Answer 38

1. increases Ca reabsorption from kidney | 2. increases Ca reabsoption from bone

Question 39

What mineral affects Ca absorption and how?

Answer 39

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

Question 40

What action of PTH indirectly affects Ca absorption?

Answer 40

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

Question 41

What organ does PTH act on?

Answer 41

kidneys

Question 42

Describe the process by which PTH increases Ca reabsorption from bone

Answer 42

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

Question 43

2 cells required for osteoclast formation

Answer 43

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

Question 44

List RANKL inducers

Answer 44

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

Question 45

List 2 RANKL inhibitors + their effect on

Answer 45

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

Question 46

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

Answer 46

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

Question 47

What is the action of OPG (osteoprotegrin)?

Answer 47

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

Question 48

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

Answer 48

calcitonin - follicular cells of thyroid gland

Question 49

What are the 2 functions of calcitonin?

Answer 49

Decreases Ca serum concentration by: 1. preventing Ca reabsorption from bone by inhibiting osteoclast differentation + activity 2. increase Ca excretion from kidney

Question 50

What is the action of vit D3 on Ca absorption?

Answer 50

Increases Ca absorption from the gut

Question 51

What are the 2 sources of vit D

Answer 51

dairy products + uv light from sun

Question 52

Daily requirement of vit D

Answer 52

400IU/daily

Question 53

Action of oestrogen in calcium + bone metabolism

Answer 53

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

Question 54

Action of glucocorticoid in calcium + bone metabolism

Answer 54

- decreases Ca absorption from gut - increases bone Ca re-absorption - consq chronic treatment = OSTEOPOROSIS

Question 55

Action of thyroxine

Answer 55

stimulates both bone formation + reabsorption