s4. CO2 in blood Flashcards
what range should arterial blood pH be kept in?
7.35-7.45
what is a buffer
compounds which are able to bind or release H+> accept/ donate > to maintain pH in narrow range
what is the reaction for the bicarbonate buffer system?
CO2 + H20 H2CO3 H+ + HCO3-
Equation to work out dissolved conc of CO2
solubility constant x pCO2
solubility constant= 0.23mmol/L/kPa
what is the law of mass action?
the rate of the reaction depends on the amounts of reactants and products
(reversible reaction)
apply the Henderson-Hasselbalch eq to the /co2-Bicarb buffer system
pH= pKa + log ([HCO3-] /[pCO2] x 0.23)
what is the ideal ratio of bicarbonate to dissolved CO2
21 (20:1)
plasma pH depends on?
- conc dissolved CO2 (controlled by breathing rate)
- conc of bicarbonate (controlled by kidneys)
- ratio of [HCO3-]:[CO2]
why is out body pH slightly alkaline?
7.4
bicarb co2 buffer is favoured slightly to producing H+ and HCO3-
what is the relationship between CO2 and pH
when CO2 inc, pH dec
which enzyme is involved in bicarbonate production in RBC?
what happens to the products?
Carbonic Anhydrase
CO2+H20–> HCO3- + H+
produced HCO3- is transported out of RBC by chloride:bicarbonate exchanger
the H+ that is also produced by the reaction is bound to haemoglobin
what is the importance of H+ binding to haemoglobin when produced in RBCs from bicarbonate production reaction?
if H+ did not bind to Hb, the reaction you;d be pushed in the opposite direction, meaning bicarbonate is used up NOT produced.
> Hb acts as a buffer
- deoxy haemorrhage is the best at binding H+!!
what controls HCO3- concentration?
kidney
made in RBC, CONTROLLEd by kidney
what happens in regards to bicarbonate buffer system when extra acid is produced as part of normal metabolism?
- acids react with HCO3- to produce CO2
- CO2 levels inc, pH dec > acidotic
- plasma bicarbonate store falls
> extra CO2 produced is removed by breathing and pH changes are buffered.
more bicarb produced to replenish buffers
compare the amount of H+ ions that bind to Hb at lungs vs at tissues
- relate this to CO2 and carbamino compounds
at lungs:
Relaxed state Hb (more O2 binds Hb) > less H+ bind
tissues:
Tense state Hb (less O2 binds Hb) > more H+ bind
*same principal with CO2 in carbamino compounds
what happens chemically when venous blood arrives at the lungs?
Hb picks up O2 > turns to R state
> Hb gives up the extra H+ that it took from the tissues
- H+ reacts with HCO3- to form CO2
> CO2 breathed out
how are carbamino compounds formed?
CO2 bind directly to Hb
at amine groups on globin of Hb
> contributes to CO2 transport
pH ranges
acidotic part of normal range is?
alkalotic?
acidotic part of normal range:
7.35-7.40
<7.35= acidotic
alkalotic part of normal range:
7.40-7.45
> 7.45= alkalotic
how to determine type of acidosis from ABG
- pCO2 elevated= respiratory acidosis
- pCO2 normal/low= NOT respiratory acidosis
- HCO3- decreased = metabolic acidosis
how to determine if there’s been any compensation for acidosis? on ABG
respiratory acidosis:
- if HCO3- elevated = compensation
full if within acidotic part of normal pH range
partial if pH<7.35
metabolic acidosis:
-pCO2 decreased= compensation
full/partial determine like above
how to determine type of alkalosis from ABG?
- pCO2 dec= respiratory alkalosis
- pCO2 normal/high= NOT respiratory alkalosis
- HCO3- inc = metabolic alkalosis
how to determine if there’s been any compensation for alkalosis? on ABG
respiratory alkalosis:
- if HCO3- dec = compensation
full if within acidotic part of normal pH range
partial if pH<7.35
metabolic alkalosis:
-pCO2 inc= compensation
full/partial determine like above
what is kyphoscoliosis? RESP implication?
Abnormal curvature of spine
Cant expand lungs
inadequate ventilation > higher pCO2
why is compensation always limited for metabolic alkalosis?
in order to compensate, pCO2 needs to inc (HYPOventilate) BUT this is problematic as it means O2 also dec and then we don’t meet our O2 demand.
