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MBBS - Year 1 > Biochem - Fracture and Dislocation > Flashcards

Biochem - Fracture and Dislocation Flashcards

1
Q

Types of bone

A

Compact/ cortical bone

Cancellous, spongy or trabecular bone

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2
Q

Cortical bone

A

High proportion of bone w/ few spaces

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3
Q

Trabecular bone

A

Low proportion of bones and a lot of space. Composed of a network of rods and plates called trabeculae

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4
Q

Bone matrix component

A

Type I collagen, bone proteoglycan, osteocalcin

Hydroxyapatite

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5
Q

Hydroxypapatite

A

A complex calcium phosphate salt helps mineralise the bone and bind the calcium into the bone

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6
Q

Patterns in which collagen can be laid down in

A

Woven bone

Lamellar bone

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7
Q

Woven bone

A

An immature form w/ random fibre orientation

Laid down during rapid growth and fracture repair

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8
Q

Lamellar bone

A

Composed of successive layers of collagen fibres w/ distinct orientation
Gives a strong structure

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9
Q

Long bones are composed of

A

Diaphysis

Epiphyses

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10
Q

Diaphysis

A

Cyclindical shaft

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11
Q

Epiphyses

A

Expanded ends of the bones

Sometimes called growth plate

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12
Q

When can bone growth occur

A

As long as the growth plate hasn’t fused

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13
Q

Bone cells

A

Osteoblasts
Osteocytes
Osteoclasts
Lining cells

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14
Q

Osteoblasts principal function

A

Bone formation, synthesising bone matrix and priming it for subsequent mineralisation

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15
Q

Osteoblasts characteristics

A

Plump cuboidal cells w/ abundant organelles for synthesis and secretion of proteins
Single nucleated
Form an epithelial layer on the bone surface

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16
Q

Lining cells

A

Osteoblasts which have completed phase of synthetic activity
Can be reactivated
Important function in bone remodelling
Possibly co-operate w/ osteocytes (communication) in regulating calcium exchange from bone

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17
Q

Osteocytes

A

Osteoblasts engulfed in bone matrix during appposition and eventually entombed within

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18
Q

Apposition

A

Laying down lamellar structure on the outer aspect of the bone

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19
Q

Most abundant cells in bone

A

Osteocytes

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20
Q

What do osteocytes rely on canaliculi for

A

Maintain junctions w/ other entombed cells and w/ bone surface therefore requires vascular supply

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21
Q

Main function of osteocytes

A

Regulation of calcium homeostasis and last act as strain gauge to monitor and record the extent of physical loading

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22
Q

Osteoclasts

A

Large multinucleate cells responsible for resorption of bone
Distinctive appearance and contains unique organelles

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23
Q

Unique organelles in osteoclasts

A

Ruffled border

Clear zone

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24
Q

Why are women bones more fragile and prone too cortical fracture

A

More endosteal resorption as opposed to periosteal apposition - men

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25
Q

How does trabecular bone change w/ age

A

Tends to diminish

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26
Q

How does cortical bone change w/ age

A

Thins

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27
Q

How is the capacity for longitudinal growth maintained

A

Persistence of epiphyseal growth cartilages

Cartilage undergoes interstitial growth and is replaced by (not transformed into) bone

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28
Q

How is the bone exposed

A

IL-6 is detected by receptors on lining cells and causes retraction

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29
Q

What happens when osteoblasts receive the signal from cytokines

A

They produce RANK ligands
RANK ligands stimulate surface receptors to produce more osteoclasts
As more are produced, osteoclasts get bigger and bigger and start resorption

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30
Q

Increased RANK ligand/ OPG ratio

A

Promotes bone loss

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31
Q

OPG production

A

Produced by osteoblasts which prevents osteoclast activation
Needs to balance w/ RANK ligand

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32
Q

Osteomalacia

A

Occurs when the bone doesn’t mineralise correctly due to vit D deficiency
Less mineralisation –> reduction in rigidity and propensity for bone to fracture

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33
Q

Defining osteoclast cell function

A 
Acid phosphatase
Glucoronidase 
Collagenase 
Metalloproteinase
Cathepsins
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34
Q

Defining osteoblast cell function

A 
Alkaline phosphatase
Osteocalcin 
Pro-collagen peptides 
Cytokines 
PTHrP
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35
Q

Body calcium

A

1 Kg is stored in the bone - broken down if body in dire need
Extracellular fluid stores 10mg/l

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36
Q

Storage form of bone

A

Calcium is stored in bone as hydroxyapatite

Phosphate is also bound in bone w/ Ca and will released when bone is broken down

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37
Q

Calcium in blood

A

Measure total calcium in blood because its cheaper
Calcium is bound to proteins in the blood
But only ionised calcium is physiologically important

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38
Q

Total [Ca]

A

2.2 -2.6 mmol/L

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39
Q

Total [Ca 2+]

A

1.1 - 1.3 mmol/L

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40
Q

Adjusted Ca =

A

Total Ca + 0.02(40-[Albumin])

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41
Q

Effect on calcium binding to proteins

A

Acidosis decreases binding, more CaPr

Alkalosis increased binding, more Ca 2+

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42
Q

Regulation of plasma calcium

A

Parathyroid hormone - most important
Binding to proteins/ PO4
Vit D
Calcitonin

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43
Q

PTH action - medium term

A

Acts on bone to stimulate osteoclast resorption

44
Q

PTH action - rapidly

A

Acts on kidneys to promote Ca being reabsorbed via the tubules so Ca re-enters the bloodstream

45
Q

PTH action - long term

A

Acts on kidney to reduce active form of vitamin D, vit D125 —> acts on intestines to improve calcium absorption in the blood

46
Q

What happens when levels of calcitonin drops

A

Removes inhibitory effect on osteoclasts allowing PTH stimulation to result

47
Q

Calcium sensing receptor modulation

A

Ca binds to Trans-membrane receptor
Acts as an antagonist decreasing PTH release
When Ca low in the presence of normal intracellular Mg PTH released from vesicles fusing w/ csm

48
Q

Calcium sensing receptor defects

A

Genetic defects can occur where the calcium sensing receptor ‘resets’ the prevailing circulating ionised (adjusted) calcium
The commonest and most important of these is where the circulating calcium is elevated in the condition Familial Benign Hypercalcaemic Hypercalciuria (FBHH) but have low Ca in urine

49
Q

The importance of RANKL

A

Tumour necrosis family
Decoy receptors osteoprotegrin
Regulates skeletal remodelling and immune function
MCSF + RANKL = osteoclastogenesis

50
Q

Roles of RANKL and OPG

A

PTH stimulates osteoblasts to produce RANKL –> stimulating osteoclasts
Oestrogen stimulates the osteoblasts to produce OPG, decreasing activity of osteoclasts

51
Q

Symptoms of hypercalcaemia

A

Aca > 2.6 mmol/L

Nausea 
Peptic ulcers 
Constipation 
Renal calculi (kidney stones) 
Polyuria 
Renal failure 
Deposition of Ca in aorta, skin etc
52
Q

Causes of hypercalcemia

A 
Hyperparathyroidism 
Hypercalcemia of Malignancy 
Toxicosis 
Sarcoid 
Vit A excess
Addisons' disease
53
Q

Symptoms of hypocalcaemia

A

Aca < 2.6 mol/L

Paresthesia 
Muscle spasms 
Tetany 
Cataracts
Neurotransmission at neuromuscular junction disrupted 
Chvostek's and Trousseau's sign
54
Q

Causes of hypocalcemia

A

Hyoparathyroidism

Vit D deficiency

55
Q

Treatment of primary hyperparathyroidism

A

Surgery - only definitive treatment

56
Q

Causes of Hypercalcaemia of Malignancy (HCM)

A

Tumours produce a factor that acts like PTH but is slightly diff, Parathyroid hormone related protein, PTHrP
More potent –> more severe hypercalcaemia

57
Q

Causes of hypothyroidism

A

Post-op (parathyroid, thyroid, cancer) - removed by accident
Idiopathic

58
Q

Why do we use Adjusted Ca

A

Of particular value in chronic disease states e.g. cancer where the decrease in albumin may mask hypercalcaemia

59
Q

Endosteum

A

Site of formation for new bone and contains osteogenic precursor cells

60
Q

Medullary cavity

A

Space within diaphysis that contains red and yellow bone marrow

61
Q

Red bone marrow

A

Produces RBC’s and WBC’s

62
Q

Yellow bone marrow

A

Contains adipose and connective tissue

Produces some WBC’s

63
Q

Metaphysis

A

Spongy bone in between epiphysis and diaphysis

64
Q

Periosteum

A

Composed of an inner layer of osteogenic cells and an outer fibrous layer

65
Q

Function of periosteum

A

Helps protect the bone
Assists in fracture repair
Helps nourish the bone tissue
Attachment point for tendons and ligaments

66
Q

Bone growth in length

A

Zone 1 - resting cartilage
Zone 2 - proliferating cartilage
Zone 3 - hypertrophic cartilage
Zone 4 - calcified cartilage

67
Q

Zone 1 - resting cartilage

A

Closest to epiphysis and made up of relatively quiescent cells
Anchors epiphyseal growth plate to the bone of the epiphysis
High matrix:cell volume allows diffusion of nutrients —> maintains chondrocytes in deeper layers

68
Q

Zone 2 - proliferating cartilage

A

Slightly larger chondrocytes – dividing and replacing ones dying at diaphyseal side of epiphyseal growth plate
Produce matrix and are responsible for longitudinal growth of the bone

69
Q

Zone 3 - hypertrophic cartilage

A

Contains 3 zones:
Maturation
Degeneration
Provisional calcification

70
Q

Maturation zone

A

Chondrocytes increase in size

Accumulate calcium within Mt

71
Q

Degeneration zone

A

Deteriorate and die

Ca is released from vesicles impregnating matrix w/ Ca salt

72
Q

Provisional calcification zone

A

No active cell growth
Necessary for invasion of metaphyseal blood vessels, destruction of cartilage cells, formation of bone along walls of calcified cartilage matrix

73
Q

Zone 4 - calcified cartilage

A

Only a few cells thick composed of dead chondrocytes (surrounded by calcified matrix)
Calcified matrix removed by osteoclasts and invaded by osteoblasts laying down new bone matrix —-> diaphyseal border firmly attached to epiphyseal growth plate

74
Q

HGF

A

Human Growth Factor

Main stimulus for growth by epiphyseal growth plates

75
Q

What is ALP a marker of

A

Bone formation

76
Q

When to check creatinine kinase levels

A

Dx of myopathies and myositis

77
Q

OPG

A

Osteoprotegrin

78
Q

Stages of normal fracture healing

A
  1. Haematoma formation
  2. Fibrocartilaginous callus formation
  3. Bony callus formation
  4. Bone remodelling
79
Q

When does haematoma formation occur

A

Between days 1-5 of the fracture healing

80
Q

Haematoma formation - fracture healing

A

Blood vessels are ruptured causing a haematoma, this clots and forms the temporary frame for subsequent healing
Pro-infl cytokines & VEGF are secreted

81
Q

Fibrocartilaginous callus formation - fracture healing

A

VEGF → angiogenesis and stem cells are recruited
Chondrogenesis occurs
Osteoprogenitor cells lay down a layer of woven bone

82
Q

Bony callus formation - fracture healing

A

RANKL is expressed so the cartilaginous callus is resorbed and begins to calcify
Woven bone continues to be laid down, forming a hard, calcified callus of immature bone

83
Q

Bone remodelling - fracture healing

A

Balance between resorption by osteoclasts and new bone formation by osteoblasts
Centre of callus replaced by cortical bone and edges replaced by trabecular bone

84
Q

When does the fibrocartilaginous callus form

A

Between days 5-11 of the fracture healing

85
Q

When does the bony callus form

A

Between days 11-28 of the fracture healing

86
Q

When does bone remodelling occur after a fracture

A

28 days and onwards

87
Q

Bone remodelling cycle

A

Activation
Resorption
Reversal
Formation

88
Q

Bone remodelling - activation

A

Recruitment and activation of osteoclast precursors (RANKL) and fusion of multiple mononuclear cells to form multinucleated preosteoclasts

89
Q

Bone remodelling - resorption

A

Osteoclasts lower the pH in the bone and secrete chemicals to digest the organic matrix resulting in Howships lacunae

90
Q

Bone remodelling - reversal

A

Regulator cytokines switch off osteoclasts

91
Q

Bone remodelling - formation

A

Osteoblasts move in and produce osteoid

92
Q

Prerequisites for normal fracture healing

A

Viability of fragments e.g. intact blood supply
Mechanical rest - either immobilisation or internal fixation
Absence of infection

93
Q

Examples of abnormal fracture healing

A

Delayed union
Non-union
Man union

94
Q

Delayed union

A

Fracture healing can take 2x as long

95
Q

Types of non-union

A

Atrophic

Hypertrophic

96
Q

Atrophic non-union

A

Too little callus has formed

97
Q

Hypertrophic non-union

A

There is obvious callus but continued instability

98
Q

Common sites of non-union

A

Scaphoid
Femoral neck
Tibial shaft

99
Q

Psuedoarthrosis

A

When a broken bone fails to heal after a fracture

The fracture structurally resembles a fibrous joint

100
Q

Common benign tumours

A

Osteoma
Osteochondroma
Giant cell tumour

101
Q

Osteoma

A

Benign ‘overgrowth’ of bone, most typically occurring on the skull

102
Q

Osteochondroma

A

Most common benign bone tumour
Cartilage-capped bony projection on the external surface of a bone
Usually in males <20 yrs

103
Q

Giant cell tumour

A

Tumour of multinucleated giant cells within a fibrous stroma
Occurs most frequently in the epiphyses of long bones
X-rays show a ‘double bubble’ appearance

104
Q

Osteosarcoma

A

Most common primary malignant bone tumour
Seen mainly in children & adolescents
Occurs most frequently in metaphyseal region of long bones prior to epiphyseal closure e.g. femur, tibia, humerus
X-rays show Codman’s triangle & sunburst pattern

105
Q

Ewing’s sarcoma

A

Small round blue cell tumour
Seen mainly in children and adolescents
Occurs most frequently in pelvis and long bones - causes severe pain
X-ray shows ‘onion skin’

106
Q

Chondrosarcoma

A

Malignant tumour of cartilage
Most commonly affects axial skeleton - palpable mass grows causing pain
More common in middle age

MBBS - Year 1 (93 decks)

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