Acid-Base Balance

Question 1

Give some examples of acids and their respective bases

Answer 1

H2CO3 (Carbonic Acid) = HCO3- Bicarbonate
HCl (Hydrochloric acid) = Cl- Chloride
NH4+ (Ammonium) = NH3 Ammonia
H2PO4- (Dihydrogen phosphate) = HPO4 2-

Question 2

What is carbonic anhydrase and what does it do?

Answer 2

Catalyst that catalyses reactions necessary for acid formation e.g. CO2 + H20 (reversible sign) H2CO3- (reversible sign) HCO3-
Carbonic anhydrase catalyses the step of CO2 reacting with water

Question 3

Why are hydrogen ions important?

Answer 3

• Very reactive
• Bind proteins like enzymes
• In order to survive an animal must control the [H+] of its blood and body fluids

Question 4

What is the {H=} that is compatible with life?

Answer 4

• 16 to 160 nEq/L of H+
• pH of 6.8 - 7.8 - outside this range = death
• ## pH of less than 7.35 or above 7.45 = pathological changes

Question 5

Why is acid-base balance important?

Answer 5

Acids and Bases have local and systemic effects on the body and its systems

Question 6

What is pH?

Answer 6

Acidity = free [H+]
pH = -log[H+]
pH and [H+} have an exponential relationship (higher nEq/L [H+] = lower pH)

Question 7

Equation

What is pKa?

Answer 7

Negative log of the acid dissociation constant (Ka) - The lower the pKa the stronger the acid
pKa = -log[Ka]

Question 8

What is Ka?

Answer 8

Ionisation constant or dissociation constant
Ka = ([H+] x [A-]) / [HA]

Question 9

What factors affect blood pH?

Answer 9

• Metabolism: CO2 from fat and CHO and H= from metabolism of proteins and fat
• Diet: Alkali in diet of vegetarians and acid in diet in carnivores/omnivores
• Disease / Drugs
• Acid/base added to the system
• Acid blown off in the form of CO2 from the lungs
• Acid or base removed mainly by kidneys but also GIT

Question 10

What is buffering?

Answer 10

• Buffer minimises pH changes
• They also act by mopping up or donating H+ ions
• If a strong acid is added to a weak acid and its conjugate salt if buffer is present dissociated H+ ions form the buffer bind to conjugate base minimising the change in pH

Question 11

What is the importance of CO2 in the bicarbonate buffer system?

Answer 11

• CO2 is removed by alveolar ventilation in the lungs keeping [CO2] relatively constant at around 40mmHg
• Any rise or fall in CO2 resulting from the loss/addition of H+ is sensed by the respiratory centres of the brainstem
• Rate of ventilation is the altered to restore the concentration