Chemical control of pH & acid base balance Flashcards
What is the bodies response to metabolic acidosis?
hyperventilation to blow of more co2 so decrease pCO2 and so decrease pH
What pneumonic can be used to be able to interpret acid- base status?
ROME - respiratory opposite (if pH high and CO2 low or pH low and CO2 high then its a respiratory cause) Metabolic equal (if pH low and HCO3- low or pH high and HCO3- high then metabolic cause?
What is the interpretation for these ABG and blood results: - pH low - CO2 high - HCO3- normal Give a likely cause
Uncompensated respiratory acidosis
Hypoventilation due to drug OD, type 2 resp failure
Why are respiratory acidosis and metabolic alkalosis hard to compensate for?
Respiratory acidosis compensation requires the kidneys to increase HCO3 recovery and produce more HCO3, this takes time.
Metabolic alkalosis compensation requires hypoventilation, which can only be done to an extent and doesn’t decrease CO2 very significantly
Interpret these results:
- pH low end of normal
- pCO2 low
- HCO3- low
compensated metabolic acidosis
- Metabolic acidosis eg due to anaerobic respiration has decreased HCO3-, but body has compensated by increasing ventilation rate to decrease pCO2 and bring the pH to normal again
What to the peripheral chemoreceptors detect? where are they found? what do they do when stimulated?
- they detect large falls in O2
- theyre found in the carotid body and aortic arch
- they increase breathing rate, increase heart rate, change blood flow distribution (more to brain, heart and kidneys)
Where are central chemoreceptors found?
the CSF of the medulla of the brain
What do central chemoreceptors detect and how?
They detect pH but only pH changes due to plasma pCO2 changes. This is because H+ and HCO3- cannot enter the CSF but pCO2 can. Therefor increases in blood pCO2= decreases in blood and CSF ph= detection by central chemoreceptors= hyperventilation to blow excess co2 off.
How will persistant increases in pCO2 (COPD) affect the central chemoreceptors?
The choroid plexus cells will increase HCO3- production to ensure the CSF pH remains within normal range. The chemoreceptors will therefor reset as pH is normal- pCO2 is still high but accepted as normal and ventilation rate will remain the same.
How much more CO2 is in blood than O2?
2.5x more
What happens when you add more CO2 to blood?
It reacts with H20 forming carbonic acid, which quickly dissociates to form H+ making the blood more acidic (pushes equilibrium to the right)
How can henderson hasselbalch equation be used to calculate blood pH?
pH= pK + log( [hco3-]/ (pCO2 x 0.23))
0.23 is solubility coefficient of CO2, so gives us [CO2]
pK is 6.1 for this reaction at 37 degrees
How much greater is the concentration of HCO3- in the blood than CO2 in the blood?
20x
How can RBCs create HCO3- when pCO2 increases?
CO2 increases in blood and so also RBCs, this drives production of HCO3 and H+ by reaction with water (catalysed by carbonic anhydrase). The RBC binds the H+ produced to negatively charged H+.
The HCO3- produced is expelled from the RBC via the chloride/ bicarbonate exchanger. Therefor increase in pCO2= increase in HCO3- production from RBCs.
In what state is Hb able to bind with H+?
In T state- low O2- at tissues. This is also where pCO2 is highest, and so RBCs are able to produce more HCO3- in response to this.
At lungs, it goes back to R state as O2 binds, the H+ is released, which reforms CO2 again which is blown off.
