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Inorganic components of saliva Flashcards

1
Q

What are the 8 inorganic components of saliva?

A
  1. Protons
  2. Bicarbonate ions
  3. Potassium ions
  4. Sodium ions
  5. Calcium
  6. Magnesium
  7. Phosphate ions
  8. Fluoride
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2
Q

What determines the pH of saliva?

A

The hydrogen ion (proton) concentration

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3
Q

Why is it important that the pH of saliva is regulated?

A
  1. Allows for optimum activity of salivary enzymes (which only operate within a restricted pH range)
  2. Determines the solubility behaviour of other salivary proteins (which will precipitate on to the tooth surface when the pH is equal to their isoelectric point, at which they have no net charge)
  3. Maintains the ionic product of hydroxyapatite
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4
Q

What do protons have a key role in?

A

Protons are key to driving the process of tooth mineral dissociation

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5
Q

What is the difference between the pH of saliva in adults and babies?

A

In adults pH tends to be in the neutral region
In babies pH tends to be more alkaline

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6
Q

What is the range of the pH in adults?

A

6-7.4

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7
Q

What causes the decrease in pH after consuming a meal?

A

Fermentation of carbohydrates by plaque micro organisms
This generates organic acids

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8
Q

Below what pH does hydroxyapatite begin to demineralises?

A

Below pH values of 5.5 (the critical pH)

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9
Q

What returns the pH back to normal after eating a meal?

A

Due mainly to salivary buffering
Reverses the remineralisation process and new mineral is precipitated

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10
Q

What is conditions are essential for remineralisation to occur

A

The pH must be above the crital pH (5.5)
Takes about 20 - 40 minutes for this to happen and salivary components play a key role in this process

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11
Q

In general what effect does increased flow rate have on salivary buffering?

A

As salivary flow rate increases, salivary buffering also increases

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12
Q

What is the relationship between flow rate and pH?

A

The higher the flow rate, the higher the resulting salivary pH

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13
Q

Why is the presence of bicarbonate ions important in saliva?

A

Because bicarbonate ions are the most important buffer in saliva and their concentration is known to change with salivary flow rate

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14
Q

What does the concentration of bicarbonate ions reflect about the glands?

A

Bicarbonate ion concentration in saliva is a reflection of the metabolic activity of the gland

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15
Q

What is the expected concentration of salivary bicarbonate in the mouth?

A

Around 15 millimolars after chewing (mechanical stimulus)
Concentrations can rise to as much as 60 millimolar.

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16
Q

What is the salivary bicarbonate concentration in unstimulated saliva?

A

Can be as low as 1 millimolar

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17
Q

What is the relationship between salivary flow and salivary bicarbonate concentration?

A

Increasing salivary flow results in increased salivary bicarbonate concentrations.

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18
Q

What is the pKa of bicarbonate and what does this mean?

A

pKa= 6.1
This means it is an excellent buffer as at pH 6.1 here will be equal concentrations of carbonic acid and bicarbonate ions

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19
Q

What is the equation for the neutralisation of H+ and HCO3-

A

H+ + HCO3- -> H2CO3 -> H20 + CO2

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20
Q

How do bicarbonate ions increase the pH?

A

H+ + HCO3- -> H2CO3 -> H20 + CO2

As the salivary pH falls, the forward reaction in the equation shown above will be favoured.
Bicarbonate ions will pick up protons and these can ultimately be eliminated entirely as water.

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21
Q

How is carbonic acid generated in the reaction of protons and bicarbonate ions?

A

Carbonic acid (and therefore bicarbonate) is generated by the action of the enzyme carbonic anhydrase, which is present in the salivary
Present in this reaction:
H2CO3 -> H20 + CO2

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22
Q

Where is carbonic anhydrase present and what reaction is it needed for?

A

It is found in the salivary glands
H2CO3 -> H20 + CO2

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23
Q

Where is bicarbonate derived from?

A

Partly derived from plasma
Partly derived from the metabolic activity of the salivary glands

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24
Q

At what concentration is carbonic acid concentration stable in the plasma?

A

1.3 Millimolars
At this pH the carbonic acid is also in equilibrium with the alveolar carbon dioxide concentration in the lungs.

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25
What is the relationship between salivary flow and carbonate ion concentration?
Carbonate ion concentration does not alter when salivary flow rate increases.
26
What are the 2 inorganic ions present in saliva?
Potassium ions Sodium ions
27
What role do potassium and sodium ions play in saliva?
Play a role in preserving electrical neutrality
28
What role do sodium ions play in maintaining electrical neutrality?
Sodium is the counter ion for bicarbonate
29
What role do potassium ions play in maintaining electrical neutrality?
Potassium is the counter ion for phosphate
30
Where is sodium pumped out of?
Sodium is actively pumped out of the primary salivary fluid as it passes along the intercallated duct of the salivary gland via sodium-potassium pumps.
31
What is the range of sodium concentration in saliva and what does it depend on
At very low salivary flow rates, sodium concentrations in the resulting saliva can be less than 10 millimolar When salivary flow rate increases, sodium concentrations can reach 30 millimolar Sodium conc depends upon the length of time that the fluid remains within the duct,
32
What can damage to the ductal cells lead to?
Increased sodium concentration
33
What can cause damage to the ductal cells
Radiotherapy
34
When are potassium ions added to saliva?
Potassium ions are added to the ductal fluid throughout its passage through the striated duct.
35
In general what does increased flow rate do to the sodium and potassium conc?
Increase in flow rate: 1. Increases sodium concentration 2. potassium ion concentrations in saliva remain relatively constant
36
State the concentration of sodium ions in stimulated and unstimulated saliva
Unstimulated: around 7.7 millimolars per litre Stimulated: 32 (+- 20) millimolars per litre
37
State the concentration of potassium ions in stimulated and unstimulated saliva
Unstimulated: 21 (+-4) millimolars per litre Stimulated: 22 (+-12) millimolars per litre
38
What is the magnesium concentration in saliva?
Quite low at around 0.4 millimolars per litre in unstimulated In stimulates around 0.2 millimolars per litre
39
What is the magnesium concentration in the ductal fluid?
Less than 1 millmolar
40
What are the possible origins of magnesium in saliva?
(Has yet to be unequivocally identified) It is possible that some contribution comes from degradation of cells within the oral environment, both host and microbial, as all cells contain relatively high levels of magnesium A small contribution may also come from dissolution of mineral during carious attack of the teeth, as we know that the earliest mineral to dissolve during acid attack of tooth mineral is unusually rich in magnesium
41
In general what happens to the magnesium conc when flow rate increases?
Magnesium ion concentration decreases
42
Why is calcium needed in saliva?
It is important in the protective functions of saliva Calcium is essential both to repair the tooth mineral (remineralisation) and to prevent mineral dissolution.
43
What is the salivary calcium ion concentration?
Around 1.5 millimolars (between 1-2 mM) (ONLY includes ionic calcium)
44
What is the relationship between flow rate and calcium ion conc?
As flow rate increases calcium ion concentration remains fairly constant
45
Where are calcium ions secreted from?
Actively secreted by the major salivary glands (Parotid gland secretion has only half the calcium content compared with submandibular saliva)
46
What is the MINOR role of phosphate ions in saliva?
Phosphate ions are capable of buffering in the physiological pH range especially in unstimulated saliva They are important buffers in plaque
47
What is the MAJOR role of phosphate in saliva ?
Phosphate ions primary role in saliva is (together with calcium) to inhibit dissolution and bring about repair of tooth mineral
48
What is the range of phosphate concentration in saliva?
Between 2 and 12 millimolars according to flow rate
49
In general what happens to the phosphate ions concentration as flow rate increases
inorganic phosphate concentrations decreases as salivary flow increases.
50
Why does the phosphate concentration decrease as salivary
1. May be due to the fact that phosphate is actively added to the secretion as it passes through the ducts and a faster transit time will result in a reduced phosphate content of the resulting saliva. 2. Increased salivary flow also produces a more alkaline pH, due to increased bicarbonate. This changes the proportions of the different ionic phosphate species which are present such that the amount of H2PO4- decreases and the amount of HPO42- and even PO43- increase
51
What is the mineral component of the mammalian skeletal tissues?
It is a calcium phosphate salt called hydroxyapatite
52
What is the formula for calcium hydroxyapatite?
Ca10(PO4)6(OH)2
53
Why is it essential for saliva to contain a sufficient amount of calcium and phosphate ions?
To maintain the solubility product for hydroxyapatite and to minimise the spontaneous precipitation out of solution of hydroxyapatite when its solubility product is exceeded
54
What happens when the concentrations of calcium and phosphate fall below the solubility product?
the tooth mineral will spontaneously dissolve, even at neutral pH.
55
What can happen is the concentration of calcium and phosphate is too high in the tooth?
Too much would lead to precipitation of mineral at other, ectopic sites within the mouth, leading to for example dental calculus formation (or “tartar”) and salivary gland stones which can block the ducts.
56
What does 'saturated in respect to salt mean'?
It is when a supernatant solution contains sufficient concentration of ions of a given salt to produce spontaneous precipitation of that salt Over and above this threshold, the solution is said to be “supersaturated
57
Saliva is _____________ with respect to hydroxyapatite at neutral pH
Supersaturated
58
What has a profound effect on the solubility product of hydroxyapatite and why?
pH has a profound effect on the solubility product for hydroxyapatite and this is due to the nature of the phosphate ion
59
What is the PO43- ion called and what does it have the ability to do?
Orhtophosphate ion It has the ability to “pick up” three protons
60
What happens to H3PO4 at a pH of 2.12?
At pH = 2.12, the concentration of H3PO4 (undissociated phosphoric acid) in solution will equal that of HPO42- (monohydrogen phosphate)
61
What happens to H3PO4 as the pH increases from 2.12?
As the pH increases further (in other words, as the concentration of hydrogen ions decreases), phosphate ions become increasingly less protonated until at pH = 7.2
62
Describe the stage of phosphate protonation stage at pH 7.2?
Half the ions are in the form of HPO42- with the remainder present as H2PO4- (dihydrogen phosphate)
63
What happens if you keep increasing the pH above 7.2?
Continued increase in pH (removing even more hydrogen ions from the solution) will ultimately see an increased amount of the PO43- ion being formed.
64
Describe the stage of phosphate protonation stage at pH 12.7?
half of the phosphate species will be present as PO43- and half as HPO42-.
65
Starting from PO43- what happens as you decrease the pH?
PO43- (12.7) HPO42- (7.2) H2PO4- (7.2) H3PO4 (2.12)
66
Starting from H3PO4 what happens as you increase the pH?
H3PO4 (2.12) H2PO4- (7.2) HPO42- (7.2) PO43- (12.7)
67
What happens at acidic conditions in regards to phosphate?
In acidic conditions, the phosphate groups will become increasingly protonated.
68
What happens at alkali conditions in regards to phosphate?
When pH is increased, the number of protonated phosphate groups will be reduced.
69
What are 4 calcium phosphate salts apart from calcium hydroxyapatite?
1. Monocalcium phosphate Ca(H2PO4)2 2. Dicalcium phosphate (CaHPO4) 3. Octacalcium phosphate Ca8(PO4)4(HPO4)2.5H2O) 4, Tricalcium phosphate Ca(PO4)2
70
What happens to calcium phosphate solubility as pH falls?
When the pH falls as a result of microbial metabolism of fermentable carbohydrate, calcium phospahte salts of increasing solubility form due to protonation of the phosphate groups in the tooth mineral Demineralsation occurs
71
When do dental caries occur?
Dental caries results when dissolution is greater than repair or when repair is for some reason prevented or impaired
72
When is saliva more supersaturated in regards to hydroxyapatite?
Saliva is more supersaturated with respect to hydroxyapatite at high flow rates so repair is favoured
73
What can dry mouthed patient suffer from?
Dry mouth patients lose both their ability to buffer acids and their ability to repair the tooth mineral when it is lost.
74
What is the fluoride concentration in saliva?
0.001-0.005 millimolars
75
When does fluoride concentration increase?
increased in plaque fluid
76
What is the relationship between salivary flow and fluoride concentration?
Salivary fluoride content varies little with flow rate.
77
What does fluoride have a profound effect on and how?
Fluoride has a profound effect on the solubility behaviour of hydroxyapatite The small fluoride ion can be incorporated into hydroxyapatite by exchanging (that is, substituting) for hydroxyl ions in the hyrdoxyapatite crystal structure, forming a mineral which is more stable and less soluble in acid.
78
What is the counter ion for phosphate in saliva (electrical neutrality)?
Potassium ions
79
Saliva is supersaturate with respect to ________ at neutral pH
Hydroxyapatite
80
Give the formula of the Orthophospahet ion and what does it have the abilty to do? PO43-
It has the abilty to pick up 3 protons
81
At what pH is the concentration of H3PO4 (undissociated phosphoric acid) in solution will equal that of H2PO4- (monohydrogen phosphate)?
2.12
82
pH has a profound affect on what due to the nature of the phosphate ion?
Hydroxyapatite
83
At what pH does the phosphate ions stop becoming less protonated?
7.2
84
At what pH are half of the phosphate species present PO43- and half as HPO42-?
12.7
85
What is the counter ion for bicarbonate ions in saliva (electrical neutrality)?
Sodium ions
86
At what pH are half the ions are in the form of HPO42- with the remainder present as H2PO4- (dihydrogen phosphate)?
7.2

IOE Dentistry - Saliva (3 decks)

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