Chemical Control of Breathing Flashcards
Define hypoxia
Fall in oxygen levels in tissue
Define hypercapnia and hypocapnia
- Hypercapnia - rise in pCO2
- Hypocapnia - fall in pCO2
Define hyperventilation and hypoventilation
- Hyperventilation - ventilation increase without change in metabolism
- pO2 will rise and pCO2 will fall
- Hypoventilation - ventilation decrease without change in metabolism
- pO2 will fall and pCO2 will rise
State the problems if pH changes beyond normal
- If pH falls below 7.0, enzymes become denatured
- If pH rises above 7.6, free calcium concentration drops leading to tetany - involuntary muscular contractions
Describe the effects on plasma pH of hyper and hypo ventilation
- Hypoventilation leads to an increase in pCO2
- Hypercapnia leads to fall in plasma pH
- Respiratory acidosis
- Hyperventilation leads to a decrease in pCO2
- Hypocapnia leads to rise in plasma pH
- Respiratory alkalosis
- Hypocapnia leads to rise in plasma pH
Define respiratory acidosis and respiratory alkalosis
- Respiratory acidosis - alveolar pCO2 rises, so [CO2] rises more than [HCO3], causing a fall in plasma pH
- Respiratory alkalosis - alveolar CO2 falls, so [CO2] falls more than [HCO3], causing an increase in plasma pH
Define compensated respiratory acidosis and compensatory respiratory alkalosis
- Compensated respiratory acidosis - persistence of respiratory acidosis causes kidneys to respond to lower pH by increasing excretion of HCO3
- Compensated respiratory alkalosis - persistence of respiratory alkalosis causes kidneys to respond to higher pH by reducing excretion of HCO3
Define metabolic acidosis and metabolic alkalosis
- Metabolic acidosis - production of acid from tissues binds to HCO3, therefore HCO3 buffering capacity decreases causing decrease in plasma pH
- Metabolic alkalosis - [HCO3] rise (eg. Vomiting) causes pH to rise
Define compensated metabolic acidosis and compensated metabolic alkalosis
- Compensated metabolic acidosis - decrease in plasma pH due to metabolic acid leads to increased ventilation to lower pCO2 and restore pH
- Compensated metabolic alkalosis - increase in plasma pH compensated by decreasing ventilation to increase pCO2
Describe the location and function of the peripheral chemoreceptors
- Carotid and aortic bodies
- Carotid bodies sit in carotid sinus where there is high blood flow (at bifurcation of carotid artery)
- Mainly detect changes in pO2 but can also detect pCO2 and pH secondarily
Describe how the body compensates for falls in pO2
Large falls in pO2 stimulate increased breathing, changes in heart rate and changes in blood flow distribution (increasing flow to brain and kidneys)
Describe the location and function of the central chemoreceptors
- Central chemoreceptors in the medulla of the brain are more sensitive to pCO2
- Small rises in pCO2 increase ventilation and small falls in pCO2 decrease ventilation
Explain the significance of the blood brain barrier in central chemoreceptors
- Blood brain barrier is only permeable to CO2 and not H+ and HCO3
- CSF [HCO3] controlled by choroid plexus cells
- Central chemoreceptors respond to changes in the pH of CSF - not pH changes in blood
Describe the short term response of the central chemoreceptors to an elevated pCO2
- Elevated pCO2 drives CO2 into CSF across blood brain barrier
- CSF [HCO3] initially constant so CSF pH falls
- Fall in CSF pH detected by central chemoreceptors
- Drives increased ventilation
- Lowers pCO2 and restores CSF pH
Describe the effect of chemoreceptors in persisting hypoxia
- Hypoxia detected by peripheral chemoreceptors - increases ventilation
- Causes pCO2 to fall further - decreases ventilation
- CSF composition compensates for the altered pCO2
- Choroid plexus cells selectively add H+ or HCO3 into CSF
- Central chemoreceptors accept the pCO2 as normal
