Control of Breathing

Question 1

Role of respiratory system (x3)

Answer 1

1. Plenish pulmonary capillary blood with O2
2. Remove CO2 from pulmonary capillary blood
3. Help maintain pH

Question 2

Consequences of respiratory impairment (x2)

Answer 2

1. Hypoxaemia: low blood O2
2. Hypercapnoae: increased blood CO2 = respiratory acidosis

Question 3

Controllers, pump and gas exchange of respiratory system

Answer 3

Controllers = respiratory centre, peripheral chemoreceptors

Pump = respiratory muscles, chest wall and airways

Gas exchange = A-C membrane

Question 4

Central Controllers: Brainstem and Cortex

Answer 4

Brainstem
- Autonomic inspiratory stimuli
- Can be overridden by cortex (e.g. holding breath)

Cortex
- Voluntary hyperventilation for hypocapnia (low blood CO2)

Question 5

Central Controllers: Sensors

• Central chemoreceptors
• Peripheral cehmoreceptors

Answer 5

CENTRAL
- Midbrain (medulla)
- Surrounded by CSF
- Respond to increase in CSF [H+] - not sensitive to decrease

PERIPHERAL
- Carotid and aortic bodies
- Respond to decreased PO2, increased PCO2 and decreased pH

Question 6

Why does increased PCO2 cause reduced blood pH?

Answer 6

1. CO2 dissolves (in blood) into carbonic acid
2. Carbonic acid dissociates into H+ and bicarbonate
3. Increased [H+] = more acidic

= reduced serum pH

Question 7

Process of increased PCO2 causing increased ventilation

Answer 7

1. Increased PCO2 = reduced blood pH
2. Reduced pH stimulates central + peripheral chemoreceptors
3. Chemoreceptors stimulate medulla to increase RR / hyperventilation

= more CO2 expelled
= reduced PCO2
= increased serum pH (return to normal)

Question 8

Ventilatory Response to Exercise

Answer 8

• Initial increase in ventilation to maintain PO2 and PCO2
• After anaerobic threshold is reached, lactic acid is produced (due to uptake limitation of glycolysis products by mitochondria)
• Lactic acid increases blood acidity:

= reduced pH
= chemoreceptor stimulation
= increased ventilation

Question 9

Type 1 vs Type 2 Respiratory Failure (Hypoventilation)

Answer 9

Type 1: Hypoxia

• Low CO2 levels is TISSUES
• Adequate ventilation but CO2 not being accumulated

Type 2: Hypoventilation

• Inadequate ventilation for metabolic demands
  = reduced breathing rate
  = reduced blood CO2 (Hypoxaemia)
  = reduced tissues CO2 (HYPOXIA)

Question 10

Respiratory Acidosis vs Metabolic Acidosis

Answer 10

RESPIRATORY ACIDOSIS:
- Hypoventilation causing failure to excrete CO2

= reduced ventilation
= increased blood CO2
= reduced blood pH (acidosis)

METABOLIC ACIDOSIS
- Excessive production or loss (consumption) of HCO3 (base)

= reduced pH (acidosis)