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MSK > Normal Bone Function > Flashcards

Normal Bone Function Flashcards

1
Q

Purpose of the skeleton

A

Raises us from the ground against gravity
Determines basic body shape
Transmits body weight
Forms jointed lever system for movement
Protects vital structures from damage
Houses bone marrow
Mineral storage- calcium, phosphorus, magnesium

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2
Q

Which minerals are stored in bone

A

Calcium
Phosphorus
Magnesium

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3
Q

Number of bones in appendicular skeleton

A

126

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4
Q

Number of bones in axial skeleton

A

80

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5
Q

What is the skeleton divided into

A

Axial
Appendicular

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6
Q

Bone classification by shape

A

Long bones
Short bones
Flat bones
Irregular bones
Sesamoid bones

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7
Q

Long bones

A

Tubular shape with hollow shaft and ends expanded for articulation with other bones

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8
Q

Short bones

A

Cuboidal in shape

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9
Q

Flat bones

A

Plates of bones
Often curved
Protective function

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10
Q

Sesamoid bones

A

Round, oval nodules in a tendon

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11
Q

Irregular bones

A

Various shapes

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12
Q

Types of bone structure- macro

A

Cortical
Trabecular

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13
Q

Cortical bone structure

A

Compact
Dense, solid, only spaces are for cells and blood vessels

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14
Q

Trabecular bone structure

A

Cancellous
Spongy
Network of bony struts (trabeculae) , looks like sponge, many holes filled with bone marrow
Cells reside in trabeculae and blood vessels in holes

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15
Q

Types of bone structure- micro

A

Woven
Lamellar

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16
Q

Woven bone

A

Made quickly
Disorganised
No clear structure

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17
Q

Lamellar bone

A

Made slowly
Organised
Layered structure

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18
Q

Function of hollow long bone

A

Keeps mass away from neutral axis
Minimises deformation

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19
Q

Function of trabecular bone

A

Gives structural support while minimising mass

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20
Q

Number of baby bones in body

A

350

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21
Q

Number of adult bones in body

A

206

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22
Q

Wide ends of bone function

A

Spreads load over weak, low friction surface

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23
Q

Flat bones function

A

Protective

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24
Q

Bone composition

A

50-70% mineral
20-40% organic matrix
5-10% water

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25
Q

Bone composition- mineral

A

Hydroxyapatite
A crystalline form of calcium phosphate

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26
Q

Hydroxyapatite

A

A crystalline form of calcium phosphate

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27
Q

Bone composition - organic matrix

A

Collagen type 1- 90% of all protein
Non-collagenous protein - 10%

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28
Q

What type of collagen composes bone

A

Type 1

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29
Q

How does collagen assemble in bone

A

Assembles in fibrils with mineral crystals situated in ‘gap’ regions between them

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30
Q

Function of mineral in bone

A

Stiffness

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31
Q

Structure of collagen in bone

A

Elasticity

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32
Q

Cells of bone

A

Osteoclasts
Osteoblasts
Osteocytes
Bone lining cell

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33
Q

Osteoclasts structure

A

Mutlinucleated

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34
Q

Osteoblasts shape

A

Plump
Cuboidal

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35
Q

Osteocyte shape

A

Stellate
Entombed in bone

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36
Q

Bone lining cell shale

A

Flattened
Lining the bone

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37
Q

Origins of osteoblasts

A

Mesenchymal stem cell

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38
Q

Function of osteoblasts

A

Form bone- in form of osteoid
Produce type 1 collagen and mineralise the extracellular matrix by depositing hydroxyapatite crystal within collagen fibrils
High alkaline phosphatase activity
Make non-collagenous proteins
Secreted factors that regulate osteoclasts - RANKL

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39
Q

Origins of osteoclasts

A

Haematopoietic stem cells

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40
Q

Function of osteoclasts

A

Resorb bone
Dissolved the mineralised matrix (acid)
Breakdown the collagen in bone (enzymatic)
High expression of TRAP and cathepsin K

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41
Q

How is the mineralised matrix dissolved

A

Acid

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42
Q

How is the collagen in bone broken down

A

Enxymes

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43
Q

Bone modelling

A

Gross shape is altered
Bone added or taken away

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44
Q

Bone remodelling

A

All of the bone is altered, new bone replaces old bone

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45
Q

Bone remodelling

A

Resting phase
Activation
Resorption
Reversal phase
Formation

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46
Q

Age of bone development -modelling

A

0-20

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47
Q

Age of bone maintenance- remodelling

A

20-50

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48
Q

Age of bone osteoporosis- acquired pathology

A

50+

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49
Q

Reasons for bone remodelling

A

Form bone shape
Replace woven bone with lamellar bone
Repair damage
Obtain calcium
Response to loading (exercise)
Reorientate fibrils and trabeculae in favourable direction for mechanical strength

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50
Q

Long bone examples

A

Humerus
Femur

51
Q

Where are Sesamoid bones found

A

Hand
Feet
Knee cap

52
Q

What can mesenchymal stem cells become

A

Adipocytes
Osteoblasts
Chondrocytes
Fibroblasts
Myoblasts

53
Q

What factors regulate osteoclasts

A

RANKL

54
Q

What do osteoclasts have a high expression of

A

TRAP
Cathepsin K

55
Q

How often do you fully replace your skeleton

A

Every 10 years

56
Q

Which hormone controls osteoclasts —-> leading to osteoporosis

A

Oestrogen

57
Q

What type of bone is the skull

A

Flat

58
Q

What type of bone is vertebrae

A

Irregular

59
Q

Where would you predominantly find trabecular bone

A

Metaphysis of long bone
Irregular bones

60
Q

Where would you predominantly find trabecular bone

A

Metaphysis of long bone
Irregular bones

61
Q

Building a collagen fibres

A

Tropocollagen
Collagen fibrils
Collagen fibres

62
Q

Amino acid sequence of collagen molecule

A

Glycine - X - Y
Up to about 1000 amino acids
X and U are often proline, hydroxyproline or hydroxylysine
Allows formation of alpha helix

63
Q

What is a biomarker of collagen synthesis

A

P1NP
P1CP

64
Q

Which amino acid is the 3rd amino acid in a collagen molecule

A

Glycine

65
Q

What forms the tropocollagen molecule

A

3 collagen chains
2 alpha-1
One alpha-2

66
Q

Number of residues per turn of collagen

A

3

67
Q

What holds the tropocollagen molecules and fibril together

A

Covalent crosslinks derived from lysine/hydroxylysine side-chains

68
Q

Processing of type 1 collagen

A

N-terminal propeptide and C-terminal propeptide cleaved to create correct length of collagen

69
Q

Structure of collagen

A

Triple helic

70
Q

Covalent cross-links within and between tropocollagen

A

-OH-lysine x2

Lysyl oxidase

71
Q

What does lysyl oxidase require

A

Copper

72
Q

Biomarkers of type 1 collagen breakdown

A

NTX
CTX

73
Q

Hydrogen bonds within tropocollagen

A

Between hydroxyproline molecules
OH-proline from proline requires Fe2+

74
Q

What does the conversion of Fe3+ to Fe2+ require

A

Vitamin C

75
Q

Cross-links between tropocollagen

A

OH-lysine x3 = pyridinolines

76
Q

Which enzymes break down collagen

A

Proteinases especially collagenases and cathepsin K

77
Q

Type 1 collagen

A

Bone, tendon, ligaments , skin

78
Q

Type 2 collagen

A

Articular cartilage
Vitreoud

79
Q

Type 3 collagen

A

Wound healing

80
Q

Type 4 collagen

A

Basal lamina

81
Q

Type 5 collagen

A

Cell surfaces

82
Q

Type 10 collagen

A

Growth plate

83
Q

What synthesises the bone matrix

A

Osteoblasts

84
Q

Other proteins found in bone matrix

A

Osteocalcin
Osteonectin
Osteopontin
Fibronectin
Bone sialoprotein
Bone morphogenetic proteins

85
Q

Function of other proteins in bone matrix

A

Contribute to structure
Regulate bone cell activity

86
Q

Bone mineralisation

A

Alkaline phosphatase hydrolyses pyrophosphate
Inorganic phosphate complexes with calcium to form hydroxyapatite
Hydroxyapatite crystals propagate along colagen

87
Q

What stimulates growth plate fusion

A

Oestrogen

88
Q

Which bones are formed by intramembranous ossification

A

Skull
Clavicles

89
Q

Which bones are formed by endochondral ossification

A

Long bones

90
Q

Appositional growth

A

Growth of bone diameter
Osteoblasts deposit bone
Osteoclasts resorb bone in the centre

91
Q

How many tropocollagen molecules pleat together

A

5

92
Q

Examples of short bones

A

Carpals
Tarsals

93
Q

At what age is peak bone mass reached

A

25

94
Q

Which enzyme is needed for bone mineralisation

A

Alkaline phosphatase

95
Q

Function of collagen in bone

A

Allows deformation (toughness)
Creates structure for hydroxyapatite

96
Q

What is common to all collagens

A

Triple helix

97
Q

Function of osteocytes

A

Maintain mineral concentration of matrix

98
Q

Woven bone

A

woven bone (primary) - appears in embryonic development and fracture repair. Consists of osteoid with the collagen fibres arranged randomly

99
Q

Lamellar bone

A

Lamellar bone (secondary) - bone of the adult skeleton. Consists of highly organised sheets of mineralised osteoid making it much stronger. It can be further subdivided into 2 types:
1. Compact bone - lamellae are organised into concentric circles which surround a vertical Haversian canal (which transmits small Neurovascular and lymphatic vessels) = osteon. Osteocytes are located between the lamellae within lacunae , and the lacunae are interconnected by canaliculi
2. Spongy bone - contains many large spaces. The bony matrix consists of a 3D network of fine columns which cross link to form irregular trabeculae- producing a light porous bone. The spaces between trabeculae are filled with bone marrow.

100
Q

Osteocytes

A

as the osteoid mineralises, osteoblasts become entombed between lamellae in lacunae where they mature into osteocytes which monitor the minerals and proteins to regulate bone mass

101
Q

Organic components of bone

A

include mainly type 1 collagen (providing tensile strength and elasticity); proteoglycans (responsible for compressive strength); matrix proteins, including osteocalcin, osteonectin and osteopontin (which promote mineralisation and bone formation); cytokines and growth factors.

102
Q

Inorganic components of bone

A

include calcium hydroxyapatite (providing compressive strength)and osteocalcium phosphate.

103
Q

Percentage of organic and inorganic components of bone

A

40% organic
60% inorganic

104
Q

Joe, a 7 year old male, comes into clinic with unexplained muscle pain and weakness. He presents with signs of scurvy - a vitamin C deficiency disease. Fe(III) is converted to Fe(II) by vitamin C and is crucial in the hydroxylation step of collagen synthesis in muscles. What is the molecule that forms hydrogen bonds within tropocollagen?

A

Hydroxyproline

105
Q

Srinath the world’s best badminton player goes to his physiotherapist with pain in what he thinks is his ligaments. However, the physiotherapist says the pain is more likely to come from tendons and she tries to explain to Srinath why this is. Which one of these is not a property of tendons?

A

High elastin content

106
Q

Strain variables

A

Rate
Magnitude
Frequency
Dwell (hold/rest periods)
Number of cycles

107
Q

What is bone formation response affected by

A

Sex
Age
Hormone
Cytokines
Drugs/medicines.nutraceuticals

108
Q

The mechanostat theory

A

There is not a single mechanostat
Our skeletons contain vast number of small units of bone, each of which has its own dynamically regulated mechanostat

109
Q

Maximising response to loading

A

Bone responds maximally to only a few loading cycles each day
Exercise in the previous 4 hours increases the response to subsequent loading
Bone responds to very brief mechanical events
Rest periods between single loading events (-10 s) increase their effect

110
Q

Which cells sense loading

A

Osteocytes

111
Q

How do osteocytes sense loading

A

Fluid flow shear stress

112
Q

Loading

A

Increases bone formation

113
Q

Off-loading

A

Decreases bone formation

114
Q

What happens to bone when they are loaded

A

Deformation and strain

115
Q

Strain

A

Change in length/ length

116
Q

Deformation

A

Force causes deformation- change in length

117
Q

How do osteocytes sense mechanical strain

A

detecting fluid shear around their dendrites in canaliculae

118
Q

How do osteocytes manage the activity of osteoblasts and osteoclasts

A

partly through direct contact with dendrites to cells on the bone surface
partly by secretion of signalling proteins such as RANKL, OPG sclerostin (there are now drug treatments for osteoporosis based on OPG and sclerostin).
Osteocytes also secrete FGF-23 which regulates phosphate excretion.

119
Q

Which of these are dietary sources of phosphate?

A

meat, dairy, soy, seeds and nuts. Carbonated soft drinks can also have high phosphate content.

120
Q

Which component of bone confers the mechanical property of stiffness?

A

Mineral

121
Q

Which hormone is the main regulator of serum calcium concentration?

A

Parathyroid hormone

122
Q

Which is a physiological function of synovial fluid?

A

Reduce friction of joint movement

123
Q

Which of the following is a source of uric acid?

A

Adenine

MSK (11 decks)

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