Role of Ventilation in Acid-Base Balance

Question 1

What is the significance of maintaining pH?

Answer 1

Maintaining pH homeostasis is important for protein function (e.g. enzyme/receptor binding sites)
They’re dependent on specific secondary, tertiary and Quaternary structures achieved via inter- and intra-chain bonding

Question 2

How are proteins denatured?

Answer 2

Various factors (pH, temperature etc) can denature proteins, by disrupting bonds and their structure - impairing function

Question 3

Why is arterial pressure so tightly regulated?

Answer 3

As the circulatory system innervates all organs and tissues, arterial pH is tightly regulated to ensure effective protein function

Question 4

How is the regulation of arterial pH achieved?

Answer 4

Due to the presence of buffering systems, and by regulating level of molecules associated with acid-base production

Question 5

How is excess H+ dealt with?

Answer 5

Presence of buffers e.g. bicarbonate buffer system:
H₂CO₃ (weak acid) + HCO₃⁻ (conjugate base)

H⁺ + HCO₃⁻ ⇆ H₂CO₃

any H⁺ formed due to the addition of a strong acid, by reacting it with a conjugate base to form a weaker acid (H₂CO₃ ) maintains a stable pH

Question 6

How are changes in pH regulated?

Answer 6

Buffers consisting of a weak acid and a conjugate base are used to resist sharp changes in pH

Question 7

Name some intracellular buffer systems

Answer 7

• phosphate buffer system
• amino acids / proteins
• Hb in RBCs

Question 8

Give some examples of extracellular buffer systems

Answer 8

• bicarbonate buffer system

- plasma proteins (e.g. albumin)

Question 9

How does CO₂ affect the acid base balance?

Answer 9

The relationship between PCO₂ and [H₂CO₃] means that CO₂ transport is important in acid base balance

Question 10

How does decreased [H⁺] lead to alkalosis and hyperventilation?

Answer 10

CO₂ + H₂O ⇆ H₂CO₃ ⇆ H⁺ + HCO₃⁻

←decreased [H⁺] = alkalosis
←decreased [H₂CO₃]
←Removal of CO₂ (hyperventilation)

Question 11

How does increased CO₂ lead to acidosis?

Answer 11

CO₂ + H₂O ⇆ H₂CO₃ ⇆ H⁺ + HCO₃⁻

→accumulation of CO₂ (hypoventilation)
→increased [H₂CO₃]
→increased [H⁺] = acidosis

Question 12

Explain the effect of CO₂ on pH

Answer 12

increased CO₂ = increased acidity

Question 13

How do the lungs affect pH?

Answer 13

As the lungs play a role in regulating CO₂ levels, they also therefore contribute to acid-base balance

Question 14

How can we diagnose respiratory distress syndrome?

Answer 14

signs of respiratory and metabolic distress can be diagnosed & interpreted from analysis of ABG and pH

Question 15

How do the lungs and kidneys maintain pH?

Answer 15

The lungs and kidneys maintain blood pH homeostasis by regulating PaCO₂ and [HCO₃⁻] respectively

Question 16

Explain the effects of PaCO₂ and [HCO₃⁻] on pH in the kidneys and lungs

Answer 16

↑PaCO₂ = ↓pH
(unless [HCO₃⁻] changes proportionally in opposite direction)
↓PaCO₂ = ↑pH

↑[HCO₃⁻] = ↑pH
(unless PaCO₂ changes proportionally in opposite direction)
↓[HCO₃⁻] = ↓pH

Question 17

What causes excessive changes in blood pH?

Answer 17

As blood pH is proportional to the ratio of HCO₃⁻ to CO₂, excessive changes may result from respiratory (CO₂) or metabolic (HCO₃⁻) dysfunction

• Decreased pH = acidosis
• Increased pH = alkalosis

Question 18

How can we differentiate between respiratory and metabolic acidosis?

Answer 18

pH < 7.35 indicates acidosis

if ↑ CO₂ = respiratory acidosis
if ↓ [HCO₃⁻] = metabolic acidosis

Question 19

How can we differentiate between metabolic and respiratory alkalosis?

Answer 19

pH > 7.45 indicates alkalosis

if ↓ CO₂ = respiratory alkalosis
if ↑ [HCO₃⁻] = metabolic alkalosis

Question 20

What are the causes of acidosis pH > 7.35?

Answer 20

Hypercapnia (hypoventilation)
↑ lactic acid (sepsis)
↑ ketone bodies (diabetes)
↓ kidney acid excretion (renal failure)
↓ HCO₃⁻ reabsorption (renal acidosis)
HCO₃⁻ loss from gut due to diarrhoea

Question 21

What are the effects of acidosis?

Answer 21

Tachypnoea

• muscular weakness
• headache
• confusion, coma
• cardiac arrhythmia
• hyperkalaemia (high K levels)

Question 22

What compensatory mechanisms are induced due to acidosis?

Answer 22

Hyperventilation
- decreased PaCO₂, respiratory compensation

Renal compensation
- decreased HCO₃⁻ excretion

Question 23

What are the causes of alkalosis > 7.45?

Answer 23

Hypocapnia (hyperventilation)
- vomiting: loss of H⁺ in HCl
↑ kidney acid excretion (diuretics)
↑ alkalotic agent consumption (antacids NaHCO₃)

Question 24

What are the effects of alkalosis?

Answer 24

Bradypnoea

• muscle weakness, cramps, tetany
• Headache, nausea
• light-headedness, confusion, coma
• cardiac arrhythmia
• hypokalaemia

Question 25

What compensatory mechanisms come into effect during alkalosis?

Answer 25

Hypoventilation
- increased PaCO₂, respiratory compensation

increased HCO₃⁻ excretion (renal compensation)

Question 26

How does acidosis induce hyperkalaemia?

Answer 26

increased [H⁺] displaces K⁺ out of the cell into ECF

=> hyperkalaemia causes vasodilation of cerebral arteries

Question 27

How does alkalosis cause hypokalemia?

Answer 27

Decreased CO₂ = decreased [H⁺] in cell so K⁺ moves into the cells to maintain balance
=> causes vasoconstriction of cerebral arteries