Chemical Control of Ventilation Flashcards
Chemoreceptors
Sensors that detect changes in pCO2, pO2, and [H+]
Central Chemoreceptors
CCRs
Found on the medulla on the brain
Sensitive to changes in H+ and pCO2
Peripheral Chemoreceptors
PCRs
Found within the aortic arch and carotid arteries
Sensitive to changes in arterial pO2
Permeability of Blood Brain Barrier
BBB is impermeable to H+ and HCO3- but permeable to CO2
How are H+ ions formed from CO2
CO2 + H2O H2CO3 HCO3- + H+
Effect of increase of pCO2 in ECF and CSF (brain) on CCRs
This increase is detected and leads to hyperventilation to decrease CO2
How do CCRs work
BBB is impermeable to H+ and HCO3-, so CO2 can diffuse and gain access to ECF and CSF, this increases pCO2. Increase in CO2 reacts with water and forms H+ and HCO3-, triggering the CCRs and causing hyperventilation for homeostasis
(Vice versa in decrease)
Effect of hyper- and hypo- ventilation on pCO2 & pO2
Hyperventilation causes an increase in pO2 and decrease in pCO2
Hypoventilation causes an increase in pCO2 and decrease in pO2
How do PCRs work
They are activated and send a signal when they detect an DECREASE in pO2
When decreased pO2 is detected, signals are sent to CNS, causing hyperventilation
What are the chemical changes if someone is exposed to a hypoventilation situation and how does the body compensate chemically
Increase in [CO2] & [H+] and decrease in pH, causing respiratory acidosis
The body compensates via the renal system where H+ excretion is INCREASED while INCREASING [HCO3-] reabsorption to maintain its buffer properties
What happens if someone is exposed to a hyperventilation situation chemically and how does the body compensate chemically
Decrease in [CO2] & [H+] and Increase in pH, causing respiratory alkalosis
The body compensates via the renal system where H+ excretion is DECREASED while DECREASING [HCO3-] reabsorption to reduce its buffer properties
What happens to respiration/ventilation during uncontrolled diabetes and how does the body compensate
The body uses ketone bodies for energy instead of fat
Ketone bodies are acidic and cause metabolic acidosis
Body compensates by hyperventilating to decrease pCO2 and increasing pH
What happens to ventilation/blood chemistry during vomiting and how does the body compensate
The body is put into alkalosis as it is ejecting an acid
The body compensates via hypoventilation to increase pCO2
Ventilation stimulus - priority of responses
pCO2 changes are the most important as CCRs are most sensitive to pCO2 changes
pH changes are next as they are usually an extension of pCO2
Then comes pO2 as the least affective since they have a wide control margin
How would the body respond to mild hypoxia at altitude and what are the consequences
Altitude causes mild hypoxia and thus body increases ventilation, decreasing pCO2. This increases CSF pH and HCO3-
Choroid plexus cells export HCO3- from CSF for pH balance
Body decides to deal with O2 decrease over caring about pH. Eventually, HCO3- is just excreted in urine to correct alkalinity
Cheyne-Stokes
Seen in individuals with CNS diseases, head trauma or heart failure
Change in breathing pattern. Patient experiences rapid breathing then the chemoreceptors detect too much CO2 so causes apnoea but then brain realises oh shit we now need CO2 so more rapid breathing as brain signal has to take over from chemoreceptors (delay)
