Integrated Control of Breathing

Question 1

What is the pH of arterial blood relative to?

Answer 1

→ Relative to the concentrations of bicarbonate ions and the partial pressure of CO2

Question 2

What regulates bicarbonate ions and in what time frame?

Answer 2

→The renal system in hours to days

Question 3

What regulates H+ ions and in what time frame?

Answer 3

→ The lungs in seconds to minutes

Question 4

How does respiratory acidosis occur?

Answer 4

→Hypoventilation because the respiratory system is not meeting the demands of the body
→pH changes because CO2 increases
→Ventilation is insufficient
→CO2 increases in the alveolar space and arterial blood (hypercapnia)
→Decrease in pH and acidosis
→ Activation of central chemoreceptors (increase ventilation rate)
→Kidneys decrease excretion of HCO3- to maintain normal pH

Question 5

What are the causes of hypoventilation?

Answer 5

→Asphyxia
→Obstructive sleep apnoea
→Increased airway resistance (COPD)
→Drug overdose (inhibits brainstem)
→Stroke
→Neuromuscular problems

Question 6

How does respiratory alkalosis occur?

Answer 6

→Hyperventilation
→pH changes because less CO2
→Increase in pH and alkalosis
→Chemoreceptors slow down breathing rate so ventilation decreases
→kidneys respond in response by excreting more bicarbonate
→pH decreases.

Question 7

What are the two causes of hyperventilation?

Answer 7

→ Emotional response

→ Altitude

Question 8

How does altitude cause hyperventilation?

Answer 8

→ The pressure of the atmosphere decreases
→ fraction of the gases stay the same.
→ The partial pressure of O2 decreases.
→ Less O2 going into the alveoli
→ Ventilation increases
→ CO2 decreases
→ pH increases

Question 9

What causes metabolic acidosis?

Answer 9

→ Sepsis
→ Diabetic ketoacidosis
→ Renal failure
→ Diarrhoea

Question 10

How does sepsis cause hyperventilation?

Answer 10

→ Septic shock
→ Decreased O2 delivery to tissues
→ Lactic acid gets produced in large amounts
→ Decreased pH
→ Tachypnoea occurs

Question 11

What causes metabolic alkalosis and how?

Answer 11

→ Diuretics
Changes to H+ and HCO3- reabsorption

→Vomiting
Loss of H+ in the stomach

→Antacids

Question 12

What is blood pH proportional to?

Answer 12

the ratio of HCO3- to CO2,

Question 13

When does respiratory acidosis occur and how is this dealt with?

Answer 13

when ventilation is insufficient relative to the metabolic demands of the body
→HCO3 excretion by kidney reduced
→increased chemoreceptor feedback
→increased respiratory rate

Question 14

How does hyperventilation occur as a result of anxiety?

Answer 14

Anxiety trigger → panic attack
→Increased ventilation (tachypnoea) without increased metabolic demand
→Hyperventilation → Decreased PaCO2
→Respiratory alkalosis
Less chemoreceptor feedback so rate slows down

Question 15

How is alkalosis as a result of increase ventilation prevented when ascending altitude?

Answer 15

try to ascend at a slow rate so that compensatory systems in the body can compensate for low pH

Question 16

What are the effects of acidosis?

Answer 16

Tachypnoea
Muscular weakness
Headache
Confusion, Coma
Cardiac arrhythmia
Hyperkalaemia

Question 17

What are the compensatory mechanisms to acidosis?

Answer 17

Hyperventilation (↓PaCO2, respiratory compensation)

↓ HCO3- excretion (renal compensation)

Question 18

What are the effects of alkalosis?

Answer 18

→ Bradypnoea
 → Muscular weakness, cramps, tetany
Headache, Nausea
Lightheadedness, confusion, coma
Cardiac arrhythmia
Hypokalaemia

Question 19

What are the compensatory effects of alkalosis?

Answer 19

Hypoventilation (↑PaCO2, respiratory compensation)

↑ HCO3- excretion (renal compensation)

Question 20

What is alkalosis-induced cerebral vasoconstriction?

Answer 20

→ CO2 (via H+) acts as a vasodilator in blood vessels (cerebral arteries particularly sensitive)
→ Hyperventilation = ↓CO2 and ↓H+ (alkalosis)
→ Alkalosis causes vasoconstriction of cerebral arteries

↓ cerebral blood flow = headache, light-headedness, confusion, seizures

Question 21

What causes acidosis-induced hyperkalaemia?

Answer 21

1. Acidosis = ↑[H+]extracellular
   2.↓H+ conc. gradient
2. ↓H+ excretion =↓H+ - Na+ exchange = ↓Na+ - K+ exchange
   4.↓Na+ - K+ exchange = ↓K+ absorption
   5.K+ accumulation in serum = hyperkalaemia
   6.Cardiac arrhythmias
   Muscle weakness

Question 22

How is minute ventilation of the lungs increased rapidly after exercise begins?

Answer 22

→ In healthy individuals, PaCO2 does not increase during exercise (in fact it may decrease slightly).

→This is because ventilation increases before the extra CO2 produced by muscles can increase PaCO2

Question 23

What is respiratory acidosis?

Answer 23

low pH and high PaCO2

due to hypoventilation

Question 24

What is respiratory alkalosis?

Answer 24

high pH and low PaCO2

due to hyperventilation

Question 25

What is metabolic acidosis?

Answer 25

low pH and low concentration of HCO3-

excessive metabolic acid production and/or increased excretion of HCO3-

Question 26

What is metabolic alkalosis?

Answer 26

High pH accompanied by high [HCO3-] is termed metabolic alkalosis, as reduced metabolic acid production or reduced excretion of HCO3-