Integrated Control of Breathing

Question 1

How do the lungs and kidneys maintain homeostasis?

Answer 1

Regulate PaCO₂ and [HCO₃⁻] respectively

Question 2

How does the CPG integrate data to maintain homeostasis?

Answer 2

The CPG integrates data from various neuronal inputs to regulate ventilation

Question 3

What determines pH of blood?

Answer 3

pH ∝ [HCO₃⁻] / PaCO₂

Blood pH is proportional to the ratio of HCO₃⁻ : CO₂,

Question 4

What can cause big changes in blood pH?

Answer 4

Excessive changes may result from respiratory (CO₂) or metabolic (HCO₃⁻) dysfunction

Question 5

How does respiratory acidosis / alkalosis occur?

Answer 5

When a change in respiratory function causes a disturbance in pH

Question 6

How does respiratory acidosis occur?

Answer 6

Hypoventilation due to an increased respiratory rate

• increases PaCO₂ (hypercapnia)
• increased [H⁺] (acidosis)

Question 7

What needs to occur to maintain blood pH during acidosis?

Answer 7

Need to decrease rate of HCO₃⁻ excretion to maintain pH balance

Question 8

What is hyperventilation caused by?

Answer 8

• asphyxia, choking etc.
• obstructive sleep apnoea
• increased airway resistance; COPD, asthma

Question 9

What is hypoventilation caused by?

Answer 9

Due to problems with initiating breathing

• drug overdose (typically opioids)
• stroke
• neuromuscular problems (motor neuron disease)
• respiratory muscle

Question 10

What causes respiratory alkalosis?

Answer 10

Alkalosis:
Due to a decreased respiratory rate; increased ventilation decreasing PaCO₂ (hypocapnia)
decreased [H⁺] (alkalosis)

Question 11

How does metabolic acidosis occur?

Answer 11

• Addition of H⁺ (reacts with available HCO₃⁻

- ↓HCO₃⁻ absorption or ↑excretion

Question 12

How does PaCO₂ affect metabolic alkalosis/ acidosis?

Answer 12

Unless PaCO₂ changes in proportion with [HCO₃⁻] in the opposite direction, acidosis will occur

Question 13

When does the respiratory system start to compensate for acidosis / alkalosis?

Answer 13

Respiratory compensation typically occurs almost instantly, but may not be enough to prevent disturbances in pH

Question 14

What are the causes of metabolic acidosis?

Answer 14

Diabetic ketoacidosis:

• increased FA release from liver due to insulin deficiency
• increases ketone body production

Renal failure
- e.g. decreased HCO₃⁻ reabsorption in proximal convoluted tubule

Diarrhoea
- e.g. decreased HCO₃⁻ absorption in colon

Question 15

What is lactic acidosis?

Answer 15

sepsis

Question 16

How does sepsis / lactic acidosis occur?

Answer 16

infection causes a pathological immune response

Causes septic shock - increasing O₂ delivery and lactate conversion

Question 17

How does metabolic alkalosis occur?

Answer 17

• removal of H⁺ so less reacts with available HCO₃⁻

- ↑HCO₃⁻ absorption or ↓excretion

Question 18

What are the causes of metabolic alkalosis?

Answer 18

Vomiting
- loss of H⁺ in stomach acid

Antacids
- increased HCO₃⁻ consumption

Diuretics
- Changes to HCO₃⁻ and H⁺ reabsorption

Question 19

What is the respiratory response to exercise?

Answer 19

In healthy individuals PaCO₂ may decrease slightly during exercise, because ventilation increases before the extra CO₂ produced by muscles can increase PaCO₂