Oxygen and carbon dioxide carriage in blood

Question 1

What is the law of mass action?

Answer 1

When a reaction is at equilibrium, the ratio of the products and substrates will remain constant

Question 2

What is the arterial content of dissolved oxygen in blood?

Answer 2

~3ml/l –> supplies 15ml/min

Question 3

What is the resting rate of O2 consumption?

Answer 3

250ml/min

Question 4

What is each Hb molecule comprised of?

Answer 4

4 polypeptide chains (globins), each with a haeme group with Fe2+ to bind to O2

Question 5

What does the arterial point of the oxyhaemoglobin dissociation curve show?

Answer 5

Has high affinity at alveoli; a large drop in P(O2) is needed before affinity starts lowering (shown by long plateau); prevents the carrying capacity of O2 from being compromised

Question 6

What does the venous point of the oxyhaemoglobin dissociation curve show?

Answer 6

Still quite high affinity with O2, but rapid drop reduces affinity rapidly

Question 7

What is P50 on the oxyhaemoglobin dissociation curve?

Answer 7

Partial pressure at which Hb is 50% saturated; ~28mmHg of O2

Question 8

What is the effect of higher P(CO2) on the oxyhaemoglobin dissociation curve?

Answer 8

Shifts right (Bohr shift)

Question 9

What is the effect of lower P(CO2) on the oxyhaemoglobin dissociation curve?

Answer 9

Shifts left

Question 10

What is the effect of higher pH on the oxyhaemoglobin dissociation curve?

Answer 10

Shifts left

Question 11

What is the effect of lower pH on the oxyhaemoglobin dissociation curve?

Answer 11

Shifts right

Question 12

What is the effect of no 2,3-DPG being present on the oxyhaemoglobin dissociation curve?

Answer 12

Shifts left; increases affinity to the extent that we can suffocate as O2 will not dissociate in tissues

Question 13

What is the effect of higher 2,3-DPG being present on the oxyhaemoglobin dissociation curve?

Answer 13

Shifts right; allows easier dissociation when at higher altitudes

Question 14

What is the effect of higher temperature on the oxyhaemoglobin dissociation curve?

Answer 14

Shifts right

Question 15

What is the effect of lower temperature on the oxyhaemoglobin dissociation curve?

Answer 15

Shifts right

Question 16

What is a useful way of determining how the oxyhaemoglobin dissociation curve will shift?

Answer 16

Think of what will happen during exercise (e.g. increased CO2, increased pH, temperature all enable easier dissociation)

Question 17

How does reduced P(O2) affect content of O2 in blood?

Answer 17

P(O2) of 28mmHg almost halves content in blood (~100.3ml/l)

Question 18

How does anaemia affect content of O2 in blood?

Answer 18

Reduced Hb almost halves content in blood (~100.3ml/l)

Question 19

How does dissolved CO2 compare to dissolved O2 in the plasma?

Answer 19

O2 ~3ml/l; CO2 ~27ml/l

Question 20

How much of the CO2 is carried dissolved in plasma?

Answer 20

~7%

Question 21

How much of the CO2 in bicarbonate ions?

Answer 21

~70%

Question 22

How much of the CO2 in Hb?

Answer 22

~23%

Question 23

What is the process of CO2 being carried in bicarbonate ion?

Answer 23

CO2 + H2O (with carbonic anhydrase as enzyme) –> carbonic acid (H2CO3). Carbonic acid quickly dissociates –> H+ and HCO3-. H+ combines with Hb –> haemoglobonic acid (HbH)

Question 24

Why is HbH important?

Answer 24

Is an important buffering action; prevents acidosis in normal conditions; when CO2 is too elevated, H+ accumulates and respiratory acidosis occurs

Question 25

How is CO2 carried in Hb?

Answer 25

Hb + CO2 –> carbaminohaemoglobin (HbCO2)