gas transport and acid base balance Flashcards
what is oxygen transported by
haemoglobin
what chains is haemoglobin made from
alpha and beta
why is the relationship sigmoidal
-between % of Hb saturation & po2
affinity for oxygen increases as haem sites become occupied
in opposite direction, dissociation of O2 accelerates as haem sites freed
which was the does the bohr effect shift
right
O2 dissociation in tissues increases with metabolism - explain
rightward shift - bohr effect
O2 affinity of Hb decreases
O2 given up by blood more easily
results from increased PCOS, H+, temp, 2,3-DPG
describe Hb
2 x alpha chains
2 x beta chains
1 atom or iron per haem binds 1 x O2
4 x O2 per Hb
how much O2 binds to Hb in 1L of arterial blood
98.5% - 197mL
in 1L of arterial blood what % of O2 dissolves directly into blood
1.5% - 3mL
what is the total O2 content in 1L of arterial blood
200mL
what does O2 binding capacity depend on
Hb concentration
how is the saturation of O2 calculated by
O2 bound to Hb/ O2 binding capacity x100
where is there high PO2
lungs
what is dissociation like for O2 in tissues
easy
foetal haemoglobin
2 x alpha chains
2 x y chains
higher affinity for oxygen
low PO2 in placenta
where is there low PO2
tissues
what is the leftward shift caused by
decreases in the same factors in the lungs
O2 affinity of Hb decreases
why does foetal Hb have a high affinity for oxygen
oxygen has to pass from the mother to the foetus
myoglobin
oxygen store in muscles
high affinity for O2 at low PO2
50% saturated at 0.6kPa O2
90% saturated at 2.6kPa O2
carbon monoxide poisoning
- CO has ~240x greater affinity for Hb compared with O2
- 50% of haem occupied by CO at only 0.1% CO in the env
-huge decrease in oxygen content of blood
- increased affinity of remaining Hb for O2
-difficult to dissociate
- PaO2 normal as gaseous makeup of inspired air remain broadly normal (CO ONLY 0.1%)
transport of CO2 via Hb
CO2 reacts with amino groups of proteins, especially Hb
formation of carbamino compounds
free H+ ion released
first step of transport of CO2 via bicarbonate
CO2 recats with H2O to form carbonic acid
primarily in RBC
CA catalyses reaction
13,000 quicker than in plasma
CO2 + H2O -> H2CO3
2nd step of CO2 transport via bicarbonate
carbonic acid dissociates into bicarbonate + free H+ ion
H2CO3 -> H+ + HCO3-
chloride shift
HCO3- exchanged for Cl- ions
bicarbonate now in blood
prevents acidification of RBC
swapped -ve for -ve
bicarbonate reacts with Na in blood = NaHCO3
what is CA stand for
carbonic anhydrase
what does CA catalyse
reaction between CO2 + H2O to form carbonic acid
CO2 in 1L arterial blood
-30% of CO2 is bound to Hb and other proteins = 147mL
-10% of CO2 is dissolved in blood = 49mL
-60% of CO2 forms bicarbonate (HCO3-) = 294mL
-TOTAL CONTENT OF ARTERIAL BLOOD = 490mL
- TOTAL CO2 CONTENT OF VENOUS BLOOD INCREASES TO 540mL
bohr and haldane effect in lungs
low CO2 increases affinity of Hb for O2
high O2 increases oxy Hb - displaces CO2
O2 = held by RBC , CO2 removed
bohr and haldane effect in tissues
high CO2 decreases affinity of Hb for O2 - BOHR
low O2 decreased oxy Hb , dexoy Hb reacts with CO2 - HALDANE
O2 removed by RBC - CO2 kept
why should H+ ions be buffered
maintain acid - base balance
pH of aterial blood = 7.4 - opt for enzyme function
held within 0.15 pH units
pH determined by H+ ion conc
tight regulation of H+ ions required
3 key mechanisms
what are the 3 key mechanisms for buffering H+ ions
reaction with Hb
reverse formation of carbonic acid
reaction with plasma proteins
what is HA
weak acid is an unionised form
what is A-
weak acid in ionised form
what is pH dependent on
conc of CO2
conc of bicarbonate/H+
conc of CO2 - pH dependency explain
determined by respiratory system
compensates for metabolic disturbances
conc of bicarbonate/H+ - pH dependency explain
determined by kidneys
compensate for respiratory disturbances
metabolic disturbances types
metabolic acidosis
metabolic alkalosis
metabolic acidosis
too much H+
- reverse bicarbonate reaction uses up H+ ions - DECREASE
- respiration increases to remove excess CO2
- pH returns to normal
CO2 + H2O <- H2CO3 -> HCO3- + H+
metabolic alkalosis
too little H+
- respiration decreases to retain CO2
- drives forward reaction, producing H+ ions (INCREASE)
- pH returns to normal
respiratory acidosis
too much CO2
- forward bicarbonate reaction uses up CO2 (DECREASES)
- bicarbonate and H+ production INCREASES
- HCO3- reabsorbed by kidneys, H+ secreted by kidneys
- pH returns to normal
CO2 + H2O -> H2CO3 -> HCO3- + H+
respiratory alkalosis
too little CO2
- kidneys retain H+
- pH returns to normal
metabolic acidosis examples
diarrhoea (HCO3- loss)
diabetic ketoacidosis
renal failure
lactic acidosis
metabolic alkalosis examples
vomiting (H+ loss0
diuretics
hypokalemia
respiratory acidosis examples
hypoventilation (COPD, airway obstruction, sedative overdose, respiratory failure
respiratory alkalosis examples
hyperventilation (in response to hypoxia, anxiety)
chloride shift
- bicarbonate (HCO3-) exchanged for chloride ions (Cl-)
-bicarbonate now in blood
- prevents acidification of RBC
-swapped a negative for a negative
- bicarbonate reacts with sodium in the blood to form sodium bicarbonate (NaHCO3)
- H+ ions?? - mopped up by deoxy Hb
- Hb reacts with H+ ions to form HHb
-favours formation of bicarbonate
-prevents the reverse reaction to CO2 + H2O
- HHb favours oxygen dissocation
-can now react with CO2
-more carbamino compounds form
- CO2 content of the blood increases
chloride shift
bicarbonate (HCO3-) exchanged for
chloride ions (Cl-)
* Bicarbonate now in blood
* Prevents acidification of RBC
* Swapped a negative for a negative!
* Bicarbonate reacts with sodium in the
blood to form sodium bicarbonate (NaHCO3)
H+ ions???
H+ ions mopped up by deoxy Hbb - chloride shift
Hb reacts with H+ ions to form HHb
* Favours formation of bicarbonate
* Prevents the reverse reaction to CO2 and H2O
* HHb favours oxygen dissociation
* Can now react with CO2
* More carbamino compounds formed
* CO2 content of the blood increases
