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MCBM Exam 3 > Biomineralization > Flashcards

Biomineralization Flashcards

1
Q

What percent of enamel is mineral?

A

99%

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2
Q

What percent of dentine is enamel?

A

70%

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3
Q

What is the purpose of organic components in mineralized tissues?

A

To provide scaffold and regulate process

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4
Q

What are the three organic components in mineralized tissues?

A

Collagen
Non-collagenous proteins
Proteoglycans

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5
Q

What is the mineral phase in mineralized tissues?

A

Calcium hydroxyapatite

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6
Q

What is enamel lacking that most other mineralized tissues have?

A

Collagen

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7
Q

In hydroxyapatite, apatite is based on what, rather than composition?

A

Structure, not composition

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8
Q

Is hydroxyapatite (HAP) a pure chemical compound?

A

Nope

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9
Q

What is a unit cell?

A

A conceptual entity representing the smallest section of a crystal

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10
Q

How many possible unit cells are there?

A

14

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11
Q

What is the lattice in crystals?

A

The pattern of repetition of the unit cells in a crystal

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12
Q

To which system of crystal structure do apatites belong?

A

hexagonal

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13
Q

What shape do naturally occurring hydroxyapaties form?

A

Hexagonal prisms and plate-like crystals

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14
Q

What is the shape of the hydroxyapatite lattice?

A

Triangular groups of 3 Ca located along c axis with each triangle rotated 60 degrees relative to the next layer

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15
Q

Where is the OH group found in a hydroxyapatite lattice?

A

In the center of the triangle, slightly above/below the plane

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16
Q

Why can’t two OH groups be oriented toward each other in hydroxyapatite lattices?

A

Space restrictions

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17
Q

What lies around each crystallite?

A

A hydration shell

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18
Q

What are the measurements of crystals in mesenchymal hard tissues?

A

150-400 angstroms long
50-100 angstroms wide
25-50 angstroms thick

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19
Q

What are the measurements of crystals in enamel?

A

1400 angstroms long
500-800 angstroms wide
250-300 angstroms thick

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20
Q

The small size of crystals in bond and dentin mean what?

A

They have enormous surface area

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21
Q

Biological apatites are ___ apatites.

A

Substituted

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22
Q

In hydroxyapatite crystals, Ca can be substituted for what ions?

A 
Na
Mg
Pb
Zn
Cu
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23
Q

In hydroxyapatite crystals, PO4 can be substituted for what ions?

A

CO3

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24
Q

In hydroxyapatite crystals, OH can be substituted for what ions?

A

Fl
Cl
CO3

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25
Q

Apatites of normal bone, enamel and dentin are principally what type of apatites?

A

Type B carbonate apatites

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26
Q

Where do ions get absorbed or bound into the apatite crystal?

A

In the hydration layer

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27
Q

3-6% of phosphate groups in bones and teeth are replaced by what groups?

A

Carbonate groups

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28
Q

Substituting carbonate groups instead of phosphate groups in the hydroxyapatite crystals has what effects?

A

Increased solubility
More susceptible to acid dissolution
Favors caries

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29
Q

What part of the teeth has the least amount of carbonate, Mg and Na

A

Enamel

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30
Q

What effects does substituting fluoride into the crystals produce?

A

Larger crystals
Decreased solubility
Promotes lesion repair

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31
Q

Substituting fluoride in the apatite crystals minimizes the incorporation of what compound?

A

HPO4

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32
Q

Substituting fluoride in the apatite crystals minimizes the negative effects of what?

A

Other ions

ex. CO3

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33
Q

How many ions come together to form a unit cell? Do they do so spontaneously?

A

18

No

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34
Q

Other types of solids form from calcium and phosphate. Where are these solids usually found?

A

In pathological conditions
Ex. Whitelock
Salivary stones

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35
Q

What compound may be another intermediate which causes enamel to grow as long plates?

A

Octacalcium phosphate

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36
Q

What is the amount of total body calcium?

A

1000g

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37
Q

How many grams of calcium are found outside of bone?

A

12g

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38
Q

About how much of our dietary calcium is excreted?

A

90%

39
Q

How much total body phosphate do we have?

A

700g

40
Q

About how much phosphate is found in muscle?

A

50g

41
Q

How much phosphate is found outside of bone?

A

100g

42
Q

What is the main source of Ca and P for bone?

A

Serum

43
Q

Where were the Ca and P ions that are incorporated in mineralized tissues found?

A

As free ions in body fluid

44
Q

What is the main source of Ca and P for the remineralization of enamel?

A

Saliva

45
Q

How are calcium and phosphate levels in biological fluids controlled?

A

Homeostatically

46
Q

What is the function of parathyroid hormone?

A

Responds to low serum calcium

47
Q

How does parathyroid hormone increase blood calcium levels?

A

By activating osteoclasts that direct bone resorption

48
Q

What does calcitonin do?

A

Responds to high serum calcium levels

49
Q

How does calcitonin reduce blood calcium levels?

A

Promotes bone formation by activating osteoblasts and inhibiting osteoclasts

50
Q

Where does vitamin D promote calcium absorption?

A

In the GI tract

51
Q

What concentration of intracellular calcium concentration trigger apoptosis?

A

Greater than 10^-6 M

52
Q

What is the concentration of extracellular calcium?

A

About 10^-3

53
Q

What are the salivary inhibitors of crystal growth?

A

Statherin
aPRPs
PPi

54
Q

pH below ___ starts to dissolve enamel leading to white spots, and eventually caries.

A

5.2

55
Q

Although tissue fluids and saliva are supersaturated in calcium and phosphate ions, does spontaneous precipitation of CaP products does not occur. Why not?

A

The energy barrier must be overcome for crystallization to occur
Inhibitors of crystal formation are present that raise the energy barrier
Intitial ioncluster may be unstable

56
Q

What conditions must be met for mineralization to be initiated?

A

Homogenous nucleation
Heterogeneous mineralization
Removal, inactivation or exclusion of inhibitors

57
Q

What is homogenous nucleation?

A

A local increase in the concentration of inorganic ions, allowing for ionic clusters to form

58
Q

What is heterogeneous mineralization?

A

Nucleating substances lower the energy barrier and allow crystalites to form without increasing the local concentrations

59
Q

What are the two ways that bone can form?

A

Endochondral ossification

Intramembranous ossification

60
Q

Which type of bone formation does not involve chondrocytes?

A

Intramembranous ossification

61
Q

Why type of bone does endochondral ossification form?

A

Long bone

62
Q

What type of bone does intramembranous ossification form?

A

Flat bone

63
Q

What are the two mechanisms for the initiation of mineralization?

A

Matrix vesicle

Mineralization of collagen fibrils

64
Q

The matrix vesicle mechanism for initiation of mineralization is found where?

A

Endochondral cartilage
Woven bone
Mantle dentin

65
Q

The mineralization of collagen fibrils mechanism of mineralization is found where?

A

Lamellar bone

Circumpulpal dentin

66
Q

What sustains crystal growth once it is initiated?

A

Supersaturated solutions

67
Q

Proteolipids from oral bacteria may make a major contribution to the formation of what?

A

Dental calculus

68
Q

What is the matrix vesicle?

A

Small, membrane bound structure that buds off a cell within first formed organic matrix

69
Q

What does the matrix vesicle contain?

A 
Alkaline phosphatase
Inorganic pyrophosphatase
ATPase
Phospholipid
Glycolipid
Polysaccharide
70
Q

The matrix vesicles may act as ___ ___ for crystal growth.

A

Nucleation sites

71
Q

How are calcium-inorganic phosphate-phospholipid complexes formed?

A

Via heterogeneous nucleation

72
Q

When the vesicle rupture, what do they provide?

A

Seeds for radial crystal growth to form calcospherules

73
Q

70-80% of mineral in bone is located where?

A

Within the fibrils

74
Q

What governs the process of collagen mineralization?

A

Non-collagenous proteins

75
Q

As governors of collagen mineralization, how do they mediate the process?

A

Some act as nucleator

Others control crystal growth

76
Q

In collagen mineralization, where does mineral first appear?

A

In gap zones at the ends of collagen molecules

77
Q

The gap zones of collagen molecules are initially filled with proteoglycan and bound calcium. How is the proteoglycan removed?

A

Proteolytically removed

78
Q

How is it thought that enamel mineralizes?

A

By crystal growth from the already mineralized dentin

79
Q

What are the two ways for calcium to reach a mineralization front?

A

Diffusion between cells

Transport through cells

80
Q

What type of junctions exist between cells in enamel formation?

A

Tight junctions

81
Q

What acts as the phosphate delivery service?

A

Alkaline phosphatase

82
Q

What does alkaline phosphatase do?

A

Hydrolyses phosphate esters with an alkaline pH optimum

83
Q

What is a possible function of alkaline phosphatase?

A

*Destroy inhibitors of HAP crystal growth
Transport of Pi
Locally increases Pi levels

84
Q

The autosomal recessive disease hypophosphatasia is due to what?

A

Mutations in TNSALP gene

85
Q

Humans have 4 specific ALP isozymes. Three are tissue specific. What are they?

A

Intestine
Placenta
Germ cell

86
Q

Where is the 4th ALP isozyme found?

A

Ubiquitous, but especially abundant in liver, bone and kidney

87
Q

What is TNSALP?

A

Tissue-nonspecificl ALP

88
Q

Where is TNSALP found?

A

It is the ubiquitous ALP isozyme

89
Q

In what demographic is hypophosphataisa most commonly seen?

A

Inbred mennonite families of Manitoba

90
Q

What is the major problem in hypophosphatasia?

A

Mineralization is defective causing:
Skeletal and/or dental issues
*premature loss of deciduous teeth

91
Q

How many forms of hypophosphatasia are there?

A

At least 6

92
Q

What is the major dental disease that comes from hypophosphatasia?

A

Odontohypophosphatasia - lack of cementum leading to:
Retarded dentinogenesis
Enlarged pulp chambers
Premature loss of teeth

93
Q

What type of crystal formation is affected by hypophosphatasia?

A

Vesicle-associated crystal formation

94
Q

What is the main effect of a loss of the TNSALP enzyme?

A

Cause increased levels of PPi that act as inhibitors of HAP crystal growth

MCBM Exam 3 (9 decks)

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