carriage of O2 and CO2 in the blood Flashcards
what are the two ways o2 is carried in the body
dissolved in blood
with haem in RBC
what is the volume of O2 in 100 ml of blood
0.29 ml
ie 0.29 ml/dl
what happens to gas in solution at low pressure
more gas dissolves in lower temperature solution
what is the equation for oxygen saturation with Haem
HbO2
HHb + HbO2
dexoy oxy
what is the volume of O2 combined with haem
So2 (saturation) x concentration of hb x huffner constant 1.39
volume of O2 combined with haem is 0.19
compared to 0.29 in the blood
what is the structure of haemo
Primary – 141-146 amino acids per chain
Secondary – globular structure
Tertiary – ‘crevice’ for haem and O2 binding
Quaternary – 4 chains (HbA = 2 x a and 2 x b)
what substances are within one Hb molecule
4 globing chains
4 haem groups
4 iron atoms
4 o2 molecules
what is the molecular basis of O2 binding
O2 binding site to haem is in a crevice
In R ‘relaxed’ form O2 can access binding site
In T ‘tense’ form O2 pushed out
difference in oxygenation in tense vs relaxed state
tense - deoxygenated
relaxed - oxygenated
describe why the Hb-O2 dissociation curve is sigmoidal
due to cooperativity between chains
at the top of the curve the haem is fully saturated
what is the difference in PO2 and SO2 of arterial and venous blood
arterial - PO2 - 12.5 kPa, SO2, 97%
venous - PO2 - 6.3 kPa, SO2 75%
how does temperature, pH and 2,3DPG affect the dissociation curve
increase in temp moves curve to the right
lower pH (more acidic) moves to the right
increase in DPG shift to the right
what does a right or left shift mean
right = decreased affinity for O2 and more unloading
what happens to DPG at high levels
increases
what are the 4 types of abnormal haem
absent globin chain (thalassaemia)
defective globin chain (HbS (sickle cells)
defective Fe atom - methaemoglobin
wrong ligand - CO
what does thalaessaemia do
alpha more severe - loss of chains - unsurvivable
what does HbS do
single amino acid defect - red cells sickle at low PO2 - haem sticks together and block passages
what is methaemoglobin
drug induced - metHb does not carry oxygen
what is the definition of a buffer
Definition: a buffer is a solution that can minimise changes in the free H+ concentration
and therefore in pH ( pH= - log10 [H+] )
what are the 4 types of buffer system and what is their capacity
bicarbonate - 18 mmol H+ per L plasma proteins 1.7 haemoglobin 8 phosphate - 0.3 total is 28
what are the three forms CO2 is carried in the blood
dissolve in the blood - temperature dependant - at 37 degrees - 3ml CO2 per dl of blood
carbamino compounds - bound to NH2-R groups on proteins on lysine and arginine = 4ml CO2 per dl of blood
as carbonic acid / bicarbonate = 45 ml CO2 per dl of blood
what catalyses the carbonic acid / bicarbonate reaction
co2 and H20 are reversible with H2CO3 via carbonic anhydrase which then goes to H+ and bicarbonate
what is the hamburger effect
HCO3- pumped out of the RBC in exchange for Cl- ion
what is the haldane effect
Oxygenation of blood in the lungs displaces carbon dioxide from hemoglobin which increases the removal of carbon dioxide
what is the H-H equation
pH = pK + log10[HCO3-]
[CO2]
pk = about 6.1
what are the two compensation systems of acid base balance
respiratory - blood pH regulates ventilation and so control PCO2 which is a rapid response
renal - excretion of H+ in urine controlled by pH - slow response
what happens during reparatory alkalosis
low PCO2 - normal HCO3 - hyperventilation (anxiety, iatrogenic)
means blood is more alkaline and PCO2 is lower than the normal patient range
higher than 7.45
what is metabolic alkalosis
normal PCO2, high HCO3- loss of H+ eg vomiting - abuse of antacid remedies blood is more alkaline and lots of HCO3- higher than 7.45
what is a respiratory acidosis
high PCO2 and high HCO3 - due to ventilatory failure = requires renal compensation
blood is more acidic
less than 7.35
what is metabolic acidosis
low HCO3 and low PCO2 = reparatory compensation - renal failure, diabetic ketoacidosis (shock)
pH less than 7.35
