Acid- Base Balance

Question 1

ACIDS

Answer 1

• Chemical species capable of releasing hydrogen (H+)ions into water
• pH is a measure of the concentration of H+ in a solution

Question 2

BUFFERS

Answer 2

• Means by which a solution resists changes in pH

- Examples of buffers in the body; proteins, phosphate buffer system,carbonic acid/bicarbonate buffer

Question 3

THE CARBONIC ACID/BICARBONATE BUFFER SYSTEM

Answer 3

• Most important one in the body is carbonic acid
• Carbonic dioxide + water ← → carbonic acid ← → bicarbonate + hydrogen ions
• These reactions occur spontaneously
• Carbonic anhydrase is an enzyme found in parts of the body including rbc and kidneys
• It accelerates the reversible reactions between carbon dioxide and water and carbonic acid

Question 4

REGULATION OF BODY FLUID pH

Answer 4

• Throughout the body: hydrogen ions are neutralised via action of buffers

2 compensatory mechanisms are used to regulate blood pH

• Removal of CO2 from body via lungs
• Secretion of H+, reabsorption of HCO3 in kidneys

Question 5

REGULATING pH BY BUFFERS

Answer 5

• If pH decreases; the increase in H+ in the body fluids will see a shift from right to left leading to a rise in pCO2 (blood carbon dioxide level)

Question 6

REGULATING pH BY RESPIRATORY COMPENSATION

Answer 6

• If pH decreases; the increase in H+ in the body fluids will see a shift from right to left leading to a rise in pCO2 (blood carbon dioxide level)
• The carbon dioxide is removed from the body via lungs→ therefore to deal with rise of H+ in the body fluids→ there needs to be greater work down by lungs
• If pH is too high; equation will shift from left to right to make up from shortfall in H+, pCO2 will drop and respiratory rate will fall allowing CO2 to build up back in the blood

Question 7

REGULATING pH BY RENAL COMPENSATION

Answer 7

• In the kidneys excess H+ ions are secreted into the urine as the filtrate travels through the tubules
• Also the kidneys will reabsorb bicarbonate from the filtrate and so prevent its loss in the urine
• These 2 processes principally involves the carbonic acid/bicarbonate buffer reaction
• Evidence for this being the pH of urine from a healthy person commonly has a pH lower than blood

Question 8

BRINGING IT ALL TOGETHER

Answer 8

3 tiers of regulation of acid- base balance
Buffer systems
The Lungs
The Kidneys

• Buffer systems regulate acid- base balance in the very short term; by utilising substances that can bind to either an acid or base
• When the carbonic acids dissociates into carbon dioxide and water, we breathe this out through the lungs, ridding the body of the acid
• Long term control of acid- base balance is managed by the kidneys, as they can adjust the pH over a long period of days by either retaining bicarbonate ions and excreting hydrogen ions