carriage of O2 and CO2 in the blood

Question 1

what are the two ways o2 is carried in the body

Answer 1

dissolved in blood

with haem in RBC

Question 2

what is the volume of O2 in 100 ml of blood

Answer 2

0.29 ml

ie 0.29 ml/dl

Question 3

what happens to gas in solution at low pressure

Answer 3

more gas dissolves in lower temperature solution

Question 4

what is the equation for oxygen saturation with Haem

Answer 4

HbO2
HHb + HbO2

dexoy oxy

Question 5

what is the volume of O2 combined with haem

Answer 5

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

Question 6

what is the structure of haemo

Answer 6

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)

Question 7

what substances are within one Hb molecule

Answer 7

4 globing chains
4 haem groups
4 iron atoms
4 o2 molecules

Question 8

what is the molecular basis of O2 binding

Answer 8

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

Question 9

difference in oxygenation in tense vs relaxed state

Answer 9

tense - deoxygenated

relaxed - oxygenated

Question 10

describe why the Hb-O2 dissociation curve is sigmoidal

Answer 10

due to cooperativity between chains

at the top of the curve the haem is fully saturated

Question 11

what is the difference in PO2 and SO2 of arterial and venous blood

Answer 11

arterial - PO2 - 12.5 kPa, SO2, 97%

venous - PO2 - 6.3 kPa, SO2 75%

Question 12

how does temperature, pH and 2,3DPG affect the dissociation curve

Answer 12

increase in temp moves curve to the right
lower pH (more acidic) moves to the right
increase in DPG shift to the right

Question 13

what does a right or left shift mean

Answer 13

right = decreased affinity for O2 and more unloading

Question 14

what happens to DPG at high levels

Answer 14

increases

Question 15

what are the 4 types of abnormal haem

Answer 15

absent globin chain (thalassaemia)
defective globin chain (HbS (sickle cells)
defective Fe atom - methaemoglobin
wrong ligand - CO

Question 16

what does thalaessaemia do

Answer 16

alpha more severe - loss of chains - unsurvivable

Question 17

what does HbS do

Answer 17

single amino acid defect - red cells sickle at low PO2 - haem sticks together and block passages

Question 18

what is methaemoglobin

Answer 18

drug induced - metHb does not carry oxygen

Question 19

what is the definition of a buffer

Answer 19

Definition: a buffer is a solution that can minimise changes in the free H+ concentration
and therefore in pH ( pH= - log10 [H+] )

Question 20

what are the 4 types of buffer system and what is their capacity

Answer 20

bicarbonate - 18 mmol  H+ per L
plasma proteins 1.7 
haemoglobin 8 
phosphate - 0.3
total is 28

Question 21

what are the three forms CO2 is carried in the blood

Answer 21

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

Question 22

what catalyses the carbonic acid / bicarbonate reaction

Answer 22

co2 and H20 are reversible with H2CO3 via carbonic anhydrase which then goes to H+ and bicarbonate

Question 23

what is the hamburger effect

Answer 23

HCO3- pumped out of the RBC in exchange for Cl- ion

Question 24

what is the haldane effect

Answer 24

Oxygenation of blood in the lungs displaces carbon dioxide from hemoglobin which increases the removal of carbon dioxide

Question 25

what is the H-H equation

Answer 25

pH = pK + log10[HCO3-]
[CO2]
pk = about 6.1

Question 26

what are the two compensation systems of acid base balance

Answer 26

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

Question 27

what happens during reparatory alkalosis

Answer 27

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

Question 28

what is metabolic alkalosis

Answer 28

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

Question 29

what is a respiratory acidosis

Answer 29

high PCO2 and high HCO3 - due to ventilatory failure = requires renal compensation
blood is more acidic
less than 7.35

Question 30

what is metabolic acidosis

Answer 30

low HCO3 and low PCO2 = reparatory compensation - renal failure, diabetic ketoacidosis (shock)
pH less than 7.35