Inorganic components of saliva Flashcards
What are the 8 inorganic components of saliva?
- Protons
- Bicarbonate ions
- Potassium ions
- Sodium ions
- Calcium
- Magnesium
- Phosphate ions
- Fluoride
What determines the pH of saliva?
The hydrogen ion (proton) concentration
Why is it important that the pH of saliva is regulated?
- Allows for optimum activity of salivary enzymes (which only operate within a restricted pH range)
- 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)
- Maintains the ionic product of hydroxyapatite
What do protons have a key role in?
Protons are key to driving the process of tooth mineral dissociation
What is the difference between the pH of saliva in adults and babies?
In adults pH tends to be in the neutral region
In babies pH tends to be more alkaline
What is the range of the pH in adults?
6-7.4
What causes the decrease in pH after consuming a meal?
Fermentation of carbohydrates by plaque micro organisms
This generates organic acids
Below what pH does hydroxyapatite begin to demineralises?
Below pH values of 5.5 (the critical pH)
What returns the pH back to normal after eating a meal?
Due mainly to salivary buffering
Reverses the remineralisation process and new mineral is precipitated
What is conditions are essential for remineralisation to occur
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
In general what effect does increased flow rate have on salivary buffering?
As salivary flow rate increases, salivary buffering also increases
What is the relationship between flow rate and pH?
The higher the flow rate, the higher the resulting salivary pH
Why is the presence of bicarbonate ions important in saliva?
Because bicarbonate ions are the most important buffer in saliva and their concentration is known to change with salivary flow rate
What does the concentration of bicarbonate ions reflect about the glands?
Bicarbonate ion concentration in saliva is a reflection of the metabolic activity of the gland
What is the expected concentration of salivary bicarbonate in the mouth?
Around 15 millimolars after chewing (mechanical stimulus)
Concentrations can rise to as much as 60 millimolar.
What is the salivary bicarbonate concentration in unstimulated saliva?
Can be as low as 1 millimolar
What is the relationship between salivary flow and salivary bicarbonate concentration?
Increasing salivary flow results in increased salivary bicarbonate concentrations.
What is the pKa of bicarbonate and what does this mean?
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
What is the equation for the neutralisation of H+ and HCO3-
H+ + HCO3- -> H2CO3 -> H20 + CO2
How do bicarbonate ions increase the pH?
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.
How is carbonic acid generated in the reaction of protons and bicarbonate ions?
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
Where is carbonic anhydrase present and what reaction is it needed for?
It is found in the salivary glands
H2CO3 -> H20 + CO2
Where is bicarbonate derived from?
Partly derived from plasma
Partly derived from the metabolic activity of the salivary glands
At what concentration is carbonic acid concentration stable in the plasma?
1.3 Millimolars
At this pH the carbonic acid is also in equilibrium with the alveolar carbon dioxide concentration in the lungs.
What is the relationship between salivary flow and carbonate ion concentration?
Carbonate ion concentration does not alter when salivary flow rate increases.
What are the 2 inorganic ions present in saliva?
Potassium ions
Sodium ions
What role do potassium and sodium ions play in saliva?
Play a role in preserving electrical neutrality
What role do sodium ions play in maintaining electrical neutrality?
Sodium is the counter ion for bicarbonate
What role do potassium ions play in maintaining electrical neutrality?
Potassium is the counter ion for phosphate
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.
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,
What can damage to the ductal cells lead to?
Increased sodium concentration
What can cause damage to the ductal cells
Radiotherapy
When are potassium ions added to saliva?
Potassium ions are added to the ductal fluid throughout its passage through the striated duct.