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3 general causes for lowering the pH in the mouth.
Acidic Drinks, Sugary Drinks/Food, Citrus Fruits. Gastric Reflux
Bacterial Metabolism (Fermentation of Sugar).
Role of a buffer and how if affects pH fluctuations
A buffer is a mechanism that works to maintain the neutrality of pH. It resists pH changes by neutralising added acids/bases. It consists of a weak acid and a conjugate base. When an acid is introduced into the environment, the conjugate base accepts the H+, neutralising the acid. When a base is introduced, the weak acid donates a H+, neutralising the base.
Strong acid
Completely dissociates in water, Lower pH, 100% ionisation in H+ and conjugate base.
Weak Acid
Partially dissociates in water, relatively low pH, equilibrium between acid and base.
Hydronium Ion
A hydronium ion is an ion that is formed when hydrogen associates with water.
pH and Scale
pH is a measurement of the amount of hydronium ions in an environment/solution. It is written on a scale from 0-14, and is calculated using pH = -log [H+]. The lower the pH is, the more acidic, hence the more H+ ions.
pH range for acidity
0 - 6.9
pH for neutrality
7
pH range for basicity
7.1 - 14
Why do biological buffers only work efficiently if their pKa is between 6 - 7.
The pKa is a pH where the amount of weak acid dissociated is 50%. Biological systems operate in a very narrow pH range (6.8 – 7.4). Hence, the pKa cant work too far outside the physiological pH range, otherwise it wont effectively neutralise.
How a weak acid (carbonic acid) acts as a pH buffer.
H2C03 > H+ + HC03-
When an acid is present in the environment, the bicarbonate ion (HC03-) reacts with the H+ ions to form H2C03, increasing pH.
When a base is present, the H+ ions react with the OH- ions, neutralising it.
Phosphate pH Buffer
DiHydrogen phosphate ion (acid) neutralises OH- ions. Hydrogen Phosphate (base) neutralises H+.
Protein pH buffer
Amino acids in proteins can donate/accept protons to raise/drop pH. In blood, hemoglobin can bind or release H+ ions to buffer blood pH.
Role of carbonic anhydrase in maintaining mouth pH
CO2dissolved + H20 > H2C03 > H+ + HC03-
As more H+ is added, HC03- works to neutralise it, forming H2C03. As the position shifts left, the H2C03 continues to form until it reaches capacity. Hence carbonic anhydrase is needed to break the H2C03 down into CO2, so that more H2CO3 can be formed in order for more HC03- to neutralise the H+.
