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MSK > Bone remodelling > Flashcards

Bone remodelling Flashcards

1
Q

What is meant by ‘Mesenchymal cells’?

Where are they found?

A

Adult stem cells traditionally found in the bone marrow.

Also found in cord blood, fallopian tube, foetal liver and lung

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2
Q

Name some cells that differentiate from Mesenchymal cells.

A

Osteoblasts
Osteocytes
Chondrocytes
Fibroblasts

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3
Q

What components make up bone?

A

50-70% minerals

20-40% organic matrix (collagen and other proteins)

5-10% water

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4
Q

Where do osteoblasts come from?

A

Mesenchymal cells in bone marrow - osteoprogenitor cells - osteoblasts

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5
Q

What do osteoblasts do?

A

‘Bone makers’

Synthesise new bone in the form of osteoid

Produce matrix vesicles rich in calcium and phosphate ions

This mineralises bone by depositing calcium hydroxyapatite crystals within collagen fibres

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6
Q

What is osteoid made of?

A

Type I collagen, GAGs, and proteoglycans

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7
Q

What characteristic does osteoid give bone?

A

Elasticity

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8
Q

What characteristic does the mineral component give bone?

A

Rigidity

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9
Q

What are osteocytes? Where are they found?

A

Inactivated osteoblasts that get trapped in mineralised bone

Lie in lacunae - small cavities

Line surface of the bone

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10
Q

What do osteocytes do?

A

Connect to each other with branches

Sense pressures of cracks in bone
Direct osteoclasts to dissolve bone

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11
Q

What is a lacuna?

A

A small cavity in which osteocytes reside

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12
Q

Where do osteoclasts come from?

A

Bone marrow derived haematopoietic cells (monocytes)

Specialised type of macrophage

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13
Q

What do osteoclasts do?

A

Erode mineralised bone

Secrete hydrochloric, carbonic, lactic & citric acids which break up hydroxyapatite

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14
Q

What is released when hydroxyapatite is broken down?

A

Calcium and phosphate

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15
Q

Osteoclasts are influenced by 2 hormones. Name them and describe.

A

PTH - stimulates osteoclast activity in response to low serum Ca

Calcitonin - inhibits osteoclast activity in response to high serum Ca

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16
Q

How many nuclei do osteoblasts and osteoclasts have?

A

Osteoblasts - 1

Osteoclasts - many

17
Q

What is bone remodelling? At what age does it stop occurring?

A

When the gross shape of a bone is altered by bone being added or taken away.

Happens up to age 20

18
Q

How is bone remodelling carried out?

A

A careful balance of…

  • new bone deposition and mineralisation by osteoblasts
  • selective resorption of formed bone by osteoclasts
19
Q

Bone mass is kept constant - how?

A

Activity of osteoblasts and clasts is well controlled

20
Q

Under which circumstances can activity levels of osteoblasts and clasts increase?

A

In response to increased physiological demand

Or in response to a fracture requiring repair and remodelling

21
Q

What reasons can mean bone needs to be remodelled?

A 
Forming bone shape
Replacing woven bone with lamellar bone
Response to exercise
Repair damage
Obtain calcium
22
Q

How is bone collagen broken down?

A

Metalloproteinases - mostly collagenases & Cathepsin K (from osteoclasts)
By osteoclasts

23
Q

What is RANK ligand?

A

A protein produced by osteoblasts and their precursor cells.

Regulates osteoclast action.

24
Q

What effect does RANK ligand have on osteoclasts? How?

A

Osteoclasts have cell surface receptors called RANK.

RANK ligand binds to it. This triggers the activation of signal pathways which promote osteoclast survival and activity.

Causing increased resorption of bone

25
Q

What is OPG?

A

Osteoprotegerin (a protein)

Secreted from osteoblasts

Binds to RANK ligand preventing it from binding to RANK

So no increase in osteoclast activity

26
Q

Briefly what do RANK ligand and OPG do?

A

RANK - increases osteoclast activity

OPG - decreases osteoclast activity

27
Q

What effect does PTH have on bone (in terms of RANK & OPG)?

A

Stimulates production of RANK ligand and reduces expression of OPG

Increasing osteoclast activity

28
Q

What effect does oestrogen have on bone (in terms of RANK & OPG)?

A

Increase expression of OPG and inhibits RANK ligand production

Reducing osteoclast activity

29
Q

In what two ways do osteoblasts & clasts communicate?

A

Coupling - bone formation occurs at sites of previous bone resorption

Balancing - amount of bone removed should equal the amount replaced

MSK (12 decks)

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