Chemical Control of Breathing Flashcards
What is HYPERCAPNIA?
A rise in pCO2
What is HYPOCAPNIA?
A fall in pCO2
What is HYPOXIA?
A fall in pO2
In exercise, how are changes in pO2 and pCO2 controlled?
In exercise, pCO2 increases and pO2 decreases
Both will be restored by increased breathing
What happens in hyperventilation?
Hyperventilation= extra breathing
- pO2 will rise
- pCO2 fall
There is no change in metabolism
What happens in hypoventilation?
A decrease in hypoventilation
- pCO2 will rise
- pO2 will fall
There is no change in metabolism
Explain why pO2 is able to fall considerably before it cause hypoxia
Oxygen binding to Hb curve is sigmoidal
meaning pO2 can drop but Hb remains saturated to an extent
What is the normal range of plasma pH and what happens if pH goes beyond these limits?
Normal plasma pH = 7.38 - 7.46
Fall below 7.0 → enzymes denature
Rise above 7.6 → concentration of [Ca2+] drops causing tetany
Explain what happens in to plasma pH in hypoventilation
Hypoventilation increases dissolved CO2 shifting the reaction to the right → increase in H+ ions causes respiratory acidosis
Explain what happens in to plasma pH in hyperventilation
Decrease in pCO2 shifts equilibrium to the left → less H+ causes pH to rise
Causes respiratory alkalosis
How do the kidneys respond to respiratory acidosis and respiratory alkalosis?
Response to respiratory acidosis= kidneys increase [HCO3-] (retain)
Response to respiratory alkalosis= kidneys decrease [HCO3-] (excrete)
How long does it take for the kidneys to respond to changes in plasma pH?
2-3 days
Explain how metabolic acidosis occurs?
Tissues producing acid react with HCO3-
Fall in HCO3- causes a drop in pH→ more acidic
Explain how metabolic alkalosis occurs?
Plasma [HCO3-] can rise after extreme vomiting → vomiting causes a rapid loss of H+ ions
Plasma HCO3- rises
How can metabolic acidosis and metabolic alkalosis be restored?
Changes in breathing
Metabolic acidosis= resolved by increased breathing
Metabolic alkalosis = resolved by decreased breathing
What do peripheral chemoreceptors detect and where are they located?
Sense changes in O2, CO2, and H+
Located in the carotid and aortic bodies
Where are central chemoreceptors located? And what do they detect?
Located in the medulla
Detect changes in H+ and increased pCO2
Explain how peripheral chemoreceptors respond to large falls in pO2
- Fall in pO2 detected by peripheral chemoreceptors
- Impulses carries by glossopharangeal and vagus nerves to the respiratory centre in the brain stem
- Increase in breathing and blood flow distribution
Explain how central chemoreceptors respond to changes in pCO2
- Increase CO2 causes increased H+ ions in CSF
- low pH detected by central chemoreceptors in medulla of brain
- Stimulates increased breathing to blow of CO2
- CO2 levels return to normal feeding back on the central chemoreceptors to return resp rate to normal
How are pCO2 and [HCO3-] levels controlled in the CSF?
- pCO2 determined by arterial pCO2
- [HCO3-] controlled by choroid plexus cells (cells that line the ventricles of the brain and produce CSF) as HCO3- cannot cross the BBB
What determines the pH of CSF?
The ratio of pCO2 : [HCO3-]
Explain how CSF pH is determines in the short vs long term
Short term: CSF pH determined by cahnges in pCO2 as the [HCO3-] is fixed due to impermeability of BBB
Long term: Choroid plexus cells respond to changes in pH to change [HCO3-]
What happens to central chemoreceptors in persisting hypoxia
Initially … Hypoxia detected by peripheral chemoreceptors to increase ventilation → pCO2 falls
If hypoxia is persistant the negative feedback doesn’t occur so the choroid plexus cells selectively add H+ or HCO3- to CSF to correct pH
As CSF pH is corrected, changes in ventilation driven by altered pCO2 dissapear and the system is set to a new normal
What do central chemoreceptors do in response to peristing hypercapnia?
- Hypercapnia causes respiratory acidosis, lowering pH of CSF
- Decrease in pH stimulates peripheral chemoreceptors in stimulate breathing
- Choroid plexus cells need to adjust to low pH to keep neurones healthy so add HCO3-
- Central chemoreceptors accept high pCO2 as the new normal
