9 Acid-Base Balance

Question 1

Why is alkalaemia more dangerous than acidaemia?

Answer 1

Alkalaemia causes calcium ions to come out of solution and bind to other molecules

Question 2

Why does alkalaemia increase neuronal excitability?

Answer 2

Lowers free calcium by causing Ca²⁺ ions to come out of solution

Also causes hypokalemia- more excitable state for neurons

Question 3

What symptoms might someone get if their blood pH reach >7.45?

Answer 3

Parasthesia and tetany (intermittent muscular spasms)

Question 4

Explain how acidaemia can cause arrhythmia. What other consequences can acidaemia have systemically?

Answer 4

• Increase K⁺ concentration in plasma
  
  • Effects excitability of muscle (esp cardiac)
• Denatures proteins
  
  • Affects glycolysis
  • Hepatic function

Question 5

What is the normal concentration of hydrogen carbonate in the blood? Where is it made and where is it controlled?

Answer 5

Question 6

Why is hydrogen carbonate concentration in plasma not depleted when we produce acid due to metabolism?

Answer 6

1. Kidney’s recover all filtered HCO₃^-
2. HCO₃^- made:
   
   1. PCT: from amino acids- put NH₄⁺ into urine
   2. DCT: from CO₂ and H₂O

Question 7

How is hydrogen carbonate reabsorbed in the proximal convulted tubule?

Answer 7

1. HCO₃^- in lumen of PCT
2. Sodium- hydrogen exchanger- pumps hydrogen ions into lumen and sodium in
3. H⁺ and HCO₃^-​ react to from H₂O and CO₂
4. H₂O and CO₂ move into tubular cell
5. Converted back into HCO₃^-​ - moves into ECF

Question 8

How is HCO₃^- created from glutamine in the PCT?

(glutamine= an amino acid)

Answer 8

Question 9

What happens to hydrogen ions and the hydrogen carbonate ions that are produced from the reaction of water and carbon dioxide in the distal tubules and collecting ducts?

Answer 9

Phosphate therefore used to create buffering system

Question 10

Outline the role of ammonia in the control of pH.

Answer 10

pH drop- increase excretion of ammonia

ammonia buffers more hydrogen ions to form amonium- ammonium trapped

Question 11

What is the minimum pH of urine? Why does the pH not go below this?

Answer 11

minimum pH: 4.5

doesn’t fall below: Due to buffering system (ie phosphate and ammonia if no HCO₃^-)

Question 12

Why does acidosis result in hyperkalaemia?

Answer 12

Reciprocal ion shift

Question 13

What effect will hypokalaemia have on acid base balance?

Answer 13

Will cause metabolic alkalosis- H+ ions move into cells

Question 14

What causes these blood levels:

Answer 14

Hypoventilation

Hypercapnia

Respiratory acidosis

Question 15

What causes these blood levels:

Answer 15

Hyperventilation

Hypocapnia

Respiratory alkalosis

Question 16

What happens to [HCO₃^-] to compensate for:

Repiratory acidosis?

Respiratory alkalosis?

How long does this take (to return to normal)

Answer 16

Question 17

What do these levels indicate?

Answer 17

Compensated respiratory acidosis

Question 18

What do these levels indicate?

Answer 18

Compensated respiratory alkalosis

Question 19

If there is a fall in [HCO₃^-] in the blood, this can lead to metabolic acidosis. Why will there not be an increase in arterial pCO₂?

Answer 19

Question 20

Which anions and cations are used to measure the anion gap?

Answer 20

Question 21

What would cause the anion gap to increase?

Answer 21

If HCO₃^- is replaced by anions from other acids (eg lactic acid)

Question 22

What condition is initially characterised by these values?

Answer 22

Metabolic acidosis

Question 23

How is metabolic acidosis compensated for?

Answer 23

Question 24

What condition is charaterised by these values?

Answer 24

Compensated metabolic acidosis

Question 25

What condition is characterised by these values?

Answer 25

Metabolic alkalosis

Question 26

Why can't metabolic alkalosis be completely compensated for by reducing breathing?

Answer 26

Need to maintain pO₂ so can only reduce breathing by so much

Question 27

What effect will type 2 respiratory failure have on pH? Give examples of what can cause type 2 respiratory failure.

Answer 27

Effect on pH: Low O₂ and High CO₂- **RESPIRATORY ACIDOSIS** (compensated for by incrase HCO₃^-)- so pH near normal Conditions causing: * Severe COPD * Severe asthma * Drug overdose (supressed ventilation) * Neuromuscular disease

Question 28

What is type 1 respiratory failure?

Answer 28

hypoxia without hypercapnia Low pO₂ and normal to low pCO₂ eg. Hypervenitlation in response to long-term hypoxia

Question 29

What is an ion gap increase indicative of? What can cause this?

Answer 29

Metabolic production of an acid

Question 30

Give examples of conditions which can cause metabolic acidosis without affecting the anion gap (ie renal related and hydrogen carbonate replaced by chloride ions)

Answer 30

Question 31

Acidosis can result in hyperkalaemia within the body. Why might diabetic ketoacidosis cause an overall depletion of potassium ion concentration?

Answer 31

Because of polyuria as a result of the diabetes- K⁺ lost in urine anyway

Question 32

Identify some causes of metabolic alkalosis:

Answer 32

Question 33

Theoretically metabolic alkalosis should be quite easy to correct ( HCO₃^-excreted) . However why might this be more difficult when there is volume depletion?

Answer 33

Question 34

Useful: thinking about metabolic acidosis

Answer 34