Integrated Control of Breathing Flashcards
What is the pH of arterial blood relative to?
→ Relative to the concentrations of bicarbonate ions and the partial pressure of CO2
What regulates bicarbonate ions and in what time frame?
→The renal system in hours to days
What regulates H+ ions and in what time frame?
→ The lungs in seconds to minutes
How does respiratory acidosis occur?
→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
What are the causes of hypoventilation?
→Asphyxia →Obstructive sleep apnoea →Increased airway resistance (COPD) →Drug overdose (inhibits brainstem) →Stroke →Neuromuscular problems
How does respiratory alkalosis occur?
→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.
What are the two causes of hyperventilation?
→ Emotional response
→ Altitude
How does altitude cause hyperventilation?
→ 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
What causes metabolic acidosis?
→ Sepsis
→ Diabetic ketoacidosis
→ Renal failure
→ Diarrhoea
How does sepsis cause hyperventilation?
→ Septic shock → Decreased O2 delivery to tissues → Lactic acid gets produced in large amounts → Decreased pH → Tachypnoea occurs
What causes metabolic alkalosis and how?
→ Diuretics
Changes to H+ and HCO3- reabsorption
→Vomiting
Loss of H+ in the stomach
→Antacids
What is blood pH proportional to?
the ratio of HCO3- to CO2,
When does respiratory acidosis occur and how is this dealt with?
when ventilation is insufficient relative to the metabolic demands of the body
→HCO3 excretion by kidney reduced
→increased chemoreceptor feedback
→increased respiratory rate
How does hyperventilation occur as a result of anxiety?
Anxiety trigger → panic attack
→Increased ventilation (tachypnoea) without increased metabolic demand
→Hyperventilation → Decreased PaCO2
→Respiratory alkalosis
Less chemoreceptor feedback so rate slows down
How is alkalosis as a result of increase ventilation prevented when ascending altitude?
try to ascend at a slow rate so that compensatory systems in the body can compensate for low pH
What are the effects of acidosis?
Tachypnoea Muscular weakness Headache Confusion, Coma Cardiac arrhythmia Hyperkalaemia
What are the compensatory mechanisms to acidosis?
Hyperventilation (↓PaCO2, respiratory compensation)
↓ HCO3- excretion (renal compensation)
What are the effects of alkalosis?
→ Bradypnoea → Muscular weakness, cramps, tetany Headache, Nausea Lightheadedness, confusion, coma Cardiac arrhythmia Hypokalaemia
What are the compensatory effects of alkalosis?
Hypoventilation (↑PaCO2, respiratory compensation)
↑ HCO3- excretion (renal compensation)
What is alkalosis-induced cerebral vasoconstriction?
→ 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
What causes acidosis-induced hyperkalaemia?
- Acidosis = ↑[H+]extracellular
2.↓H+ conc. gradient - ↓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
How is minute ventilation of the lungs increased rapidly after exercise begins?
→ 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
What is respiratory acidosis?
low pH and high PaCO2
due to hypoventilation
What is respiratory alkalosis?
high pH and low PaCO2
due to hyperventilation
What is metabolic acidosis?
low pH and low concentration of HCO3-
excessive metabolic acid production and/or increased excretion of HCO3-
What is metabolic alkalosis?
High pH accompanied by high [HCO3-] is termed metabolic alkalosis, as reduced metabolic acid production or reduced excretion of HCO3-
