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LOCO > 4 - Bone Metabolism > Flashcards

4 - Bone Metabolism Flashcards

1
Q

What are the 2 types of bone

A

Lamellar

Woven

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2
Q

What are the 2 types of lamellar bone

A

Cortical/compact

Cancellous/trabecular/spongey

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3
Q

Feature of lamellar bone

A

Has a layered organisation

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4
Q

Features of cortical//compact bone

A

Makes up the outside of a bone to give strength and structure
80% of total bone mass

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5
Q

Cancellous/trabecular bone

A

Thin in diaphysis and most in head/neck, lighter
20% of total bone mass
10x SA of cortical bone

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6
Q

Features of Woven bone

A

Random collagen organisation
Mechanically weak and forms quickly
Immature
Used in healing and can be pathological

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7
Q

What bone marrow fills bone in adults

A

Yellow bone marrow

lies in the medullary cavity

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8
Q

Where is bone marrow in adults

A

In spongy bones of vertebrae, rib, sternum, cranium and epiphyses of long bones

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9
Q

Composition of bone matrix

A

35-40% organic = Type 1 collagen, proteoglycans, growth factors
70% inorganic = 95% Calcium hydroxyapatite
5% water

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10
Q

Osteoprogenitor cell

A

In the outer membrane

Can become an osteoblast

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11
Q

Osteoblast

A

Cells that form new bone

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12
Q

Osteocyte

A

Detects stresses in the ECM and produces bone collagen to maintain the bone matrix

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13
Q

Osteoclast

A

Large cells that dissolve the bone

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14
Q

Canaliculi

A

Canals that connect osteocytes together

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15
Q

Haversian Canals

A

Tubes which form a network and contain blood vessels

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16
Q

What signals remodelling

A

Death of osteocytes

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17
Q

Reasons for remodelling

A

Renews bone before deterioration

Redistributes bone matrix along mechanical stress line

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18
Q

What is Sclerostin

A

A secreted glycoprotein

Inhibits osteoblasts to prevent bone formation

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19
Q

What inhibits and increases Sclerositin

A

PTH and mechanical stress inhibits sclerostin

Calcitonin increases

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20
Q

What secretes sclerostin

A

Osteocytes

they secrete sclerostin when not under mechanical stress to prevent new bone formation

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21
Q

What is Ephirin B2

A

A ligand expressed by osteoclasts

22
Q

What is Eph B4

A

A receptor expressed on osteoblasts

23
Q

What increases Ephrin B2 expression

A

PTH

24
Q

What happens when the ephrinb2 ligant attaches to the ephb4 receptor

A

• Generates bidirectional anti-osteoclastogenic and pro-osteoblastogenic signals.
• Inhibits osteoclast precursor differentiation and enhances osteoblast differentiation.
MORE BONE

25
Q

Stages of bone remodelling

A

1) Osteoclast attaches to bone forming a leak proof seal
2) Osteoclast secretes HCL, and protein-digesting enzymes
3) The protein digesting enzymes break down collagen fibres
4) The Acid dissolves bone minerals
5) Proteins and minerals cross osteoclast to exit into interstitial fluid to be reused
6) Osteoclast will unclamp and then clamp again along the bone and forms a groove behind it
7) Osteoblasts produced fill lacuna with osteoid
8) The osteoid secretes collagen and protein
9) The osteoid is mineralised approx 1 week later

26
Q

What can be used as a bone marker to measure if mineralisation was taking place

A

Tetracycline

27
Q

How much calcium in adult body

A

1100g

28
Q

How much of calcium in our body is in our skeleton

A

1%

29
Q

Serum calcium level

A
  1. 2- 2.6mmol/L

8. 5-10.5 mg.dL

30
Q

How much serum calcium is free ionised calcium

A

1.0-1.25mmol/L

31
Q

What is free ionised calcium

A

The physiologically important component which is free and active

32
Q

What does maintenance of normal serum calcium depend on

A

Intestinal absorption
Renal excretion
Skeletal mobilisation

33
Q

Recommended daily intake of calcium

A

500-1300mg

34
Q

Calcium extcreted

A

Kidneys - 200mg/day

Gut - 600-800mg/day in stools

35
Q

How much phosphate in the adult body

A

500-800g

36
Q

Hydroxyapatite

A

80-90% in skeleton and 10% in blood/plasma

37
Q

Normal plasma conc of phosphate

A

0.8-1.5mmol/L

38
Q

What stimulates PTH to be secreted from the parathyroid gland

A

Low plasma ca2+

39
Q

What does PTH promote

A

Ca2+ reabsorption from kidney
PO4 excretion (more PO4 excreted and less Ca)
Ca2+ reabsorption from bone (does this by increasing the no of osteoclasts)
Synthesis of 1,25-dihydroxyvitamin D (1,25 (OH)2 vitamin D3). (RANKL inducer)

40
Q

How does PTH increase the number and activity of osteoclasts

A

PTH/vitamin Dis released
PTH binds to PTH receptors on osteoblasts
This causes the RANK-L to be produced
RANK-L binds to RANK receptor on osteoclast
Causes osteoclast activity

41
Q

What does 1,25 (OH)2 vitamin D3). do

A

increase Ca2 absorption from the gut

induces RANKL

42
Q

What is M-CSF

A

Macrophage colony stimulating factor

Osteoclast needs this to be activated

43
Q

What produces MCSF and RANKL

A

Osteoblasts

Stromal cells

44
Q

What is OPG (Osteoprotegrin)

A

A RANKL inhibitor

IT is a decoy receptor for RANKL so RANKL will bind however osteoclasts are not activated

45
Q

What is released when plasma levels of Ca2+ are too high

A

Calcitonin

When Ca2+ >2.25mmol/L

46
Q

What does calcitonin do

A

inhibits osteoclast differentiation and activity
increases Ca2+ excretion from kidney
Inhibits Ca2+ absorption by intestines

47
Q

What is the Vitamin D requirement a day

A

400IU/day

48
Q

What can 1,25 (OH)2 vitamin D3 do?

A

Strongly stimulates Ca2+ absorption from gut
Stimulates bone resorption in same way as PTH
Production of pro-collagen type I
Productionof alkaline phosphatase matrix vesicles

49
Q

How does oestrogen affect bone metabolism

A

In the gut it increases Ca2+ absorption

In the bone it causes decreased reabsorption (inhibits osteoclasts)

50
Q

How does glucocorticoids affect bone metabolism

A

In the gut they decrease ca2+ absorption
In the bone they increase reabsorption + decreases formation
Prolonged corticosteroid treatment can cause osteoporosis

51
Q

How does progesterone affect bone metabolism

A

Increases bone density

52
Q

Where is calcitonin released from

A

Thyroid gland

LOCO (25 decks)

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