Control of Breathing

Question 1

How is breathing initiated and controlled?

What are the types of chemoreceptors?

Answer 1

• Initiated by motor neurons from the DRG (Dorsal respiratory group) and VRG (Ventral respiratory group) in the medulla. It is modulated by sensory receptors around the body.

DRG - initiates inspiration by innervating inspiratory muscles
VRG - initiates expiration by innervating expiratory muscles.

• Central chemoreceptors: found in medulla - detect changes in arterial CO2 and CSF PH
  Peripheral chemoreceptors: found in carotid/aortic bodies - detect changes in arterial O2, CO2, PH.

Question 2

What is sleep apnoea?

What are the types of sleep apnoea?

Answer 2

• The temporary cessation of breathing during sleep.
• Obstructive sleep apnoea: blockage of upper respiratory tract - due to tongue displacement, fat deposition (pressure on neck), relaxation of pharyngeal dilator muscles.
  Central sleep apnoea: dysfunction in the process that initiates breathing - due to stroke (damage to resp. centres), drugs, neonates (still developing), brainstem trauma.

Question 3

What is Respiratory Acidosis? Causes?

Answer 3

Due to hypoventilation, as there’s ↑pCO2 = ↓PH. This drop in PH will increase chemoreceptor feedback to ↑ventilation.

Hypoventilation caused by choking, obstructive sleep apnoea, asthma, COPD.

To maintain normal PH in the long term, ↓HCO3- excretion must occur. More CO2 will be made due to buffer system.

Question 4

What is Respiratory Alkalosis? Causes?

How do high altitudes cause respiratory alkalosis?

Answer 4

• Due to hyperventilation, as there’s ↓HCO3- = ↑PH. This rise in PH will decrease chemoreceptor feedback to ↓ventilation.

Hyperventilation caused by anxiety.

To maintain normal PH, ↑HCO3- must occur. Less CO2 will be made due to buffer system.

• At high altitudes, there’s less O2 present, so hyperventilation occurs to maintain pO2 (hypoxic drive). This will ↓pCO2 = ↑PH

Question 5

What is Metabolic Acidosis? Causes?

Answer 5

Due to the excessive acid production and HCO3- excretion.

This can be due to sepsis, diabetic ketoacidosis, renal dysfunction.

Respiratory compensation occurs to ↑pO2 and lactic acid conversion. Compensation may not be enough to prevent PH change.

Question 6

What is Metabolic Alkalosis? Causes?

Answer 6

Due to excessive acid excretion, HCO3- reabsorption, and deficient HCO3- GI absorption.

This can be due to diuretics, diarrhoea, vomiting, antacids, renal dysfunction.

Respiratory compensation occurs to ↓pO2. Compensation may not be enough to prevent PH change.

Question 7

What is acidosis-induced hyperkalaemia?

What is alkalosis-induced cerebral vasoconstriction?

Answer 7

• Acidosis = ↓H/Na exchange and Na/K exchange = ↓K+ absorption into cell = Hyperkalaemia (can cause arrhythmias)
• CO2 acts as vasodilator in cerebral artery. Alkalosis = vasoconstriction of cerebral arteries = ↓cerebral blood flow (causes headaches, confusion, seizures)