Lecture 12: Gas transport in blood

Question 1

how is oxygen transported in blood?

Answer 1

98. 5% oxygen transported bound to Hb - 4 molecules of oxygen per Hb molecule.
99. 5% dissolved in plasma

Question 2

what does the oxygen-haemoglobin saturation curve describe?

Answer 2

saturation of Hb - amount of O2 bound to Hb

Question 3

is the relationship between % saturation of Hb and PO2 linear or non linear and why?

Answer 3

non-linear –> sigmoid curve

because affinity of Hb for O2 changes with number of O2 bound molecules

Question 4

does Hb load or unload when PO2 is high?

Answer 4

Hb loads with O2 when PO2 high, unloads where O2 is low

Question 5

does increasing PO2 result in an increase in binding to Hb, why?

Answer 5

no it does not

Hb already almost 100% saturated at PO2 = 100mmHg

Question 6

the bohr describes a left or right shift of the oxygen-haemoglobin saturation curve?

Answer 6

RIGHT

Question 7

what 3 instances does the bohr effect occur?

Answer 7

• increased blood PCO2 or H+ - binding of CO2 reduces affinity of Hb for O2, increase in H+ during exercise, results from both increase in PCO2 and lactic acid
• increase blood temperature (high in tissues/lower in lung during exercise)
• DPG: present in RBC at varying levels depending on physiological status of individual

Question 8

what does the bohr effect result in?

Answer 8

a readier dissociation of O2 from haemoglobin at mid-range PO2 levels = advantageous in exercising muscle

Question 9

how is carbon dioxide transported around the body?

Answer 9

60% as HCO3- , 30% bound to Hb, 10% dissolved in plasma

Question 10

how and where is carbonic acid from CO2 produced?

Answer 10

catalysed by carbonic anhydrase within RBC
CO2 + H2O H2CO2 H+ + HCO3-
Reaction driven to left in lungs, driven to right in peripheral circulation

Question 11

what is the chloride shift?

Answer 11

in peripheral circulation HCO3- removed by diffusion out of the RBC in exchange for Cl to maintain electrical neutrality

Question 12

does reduced Hb have a greater affinity for CO2 or for O2? what is this known as

Answer 12

greater affinity for both CO2 and H+ than does HbO2

known as the haldane effect

Question 13

what is the haldane effect

Answer 13

Haldane effect describes the influence of O2 to affect the affinity of Hb for CO2 and H+

When O2 bound to Hb, decreases affinity for CO2 and H+ to HB

Question 14

describe the bonging of oxygen to Hb within the lung

Answer 14

in lungs have high PaO2
this decreases Hb unloading/increases O2 loading to Hb
via the Haldane effects decreases the CO2 and H+ update
via the Bohr effect increasing the amount of O2 bound

Question 15

describe the bonging of oxygen to Hb within the tissue

Answer 15

in tissue have decreases PaO2, therefore there is increased unloading of O2 from Hb
via the haldane effect increasing CO2 and H+ uptake by Hb because less O2 on Hb, amplifies the O2 unload
via the Bohr effect more CO2 and H+ bound, amplifies unloading of O2

Question 16

what is the Bohr effect?

Answer 16

Bohr effect describes influence of CO2 and H+ to affinity of Hb affinity for O2

when CO2 and H+ bound, decreases Hb affinity for O2

Question 17

what is normal blood pH

Answer 17

around 7.4

Question 18

how does respiratory acidosis arise?

Answer 18

can result from increased PCO2 in blood, resulting from inadequate ventilation, carbonic anhydrase located in RBD and H+ can’t diffuse out readily

Question 19

what is metabolic (non-respiratory) acidosis, how does it arise?

Answer 19

increase in [H+] of blood relative to [HCO3-]
occurs: during heavy exercises lactic acid accumulates due to shift in anaerobic metab
occurs as a result of ketoacidosis, in diabetes or any physiological stress e.g. pregnancy
or when HCO3- lost from body e.g. in severe diarrhoea

Question 20

how does respiratory alkalosis arise?

Answer 20

decreased PCO2 in blood resulting from hyperventilation

Question 21

what is metabolic (non-resp) alkalosis, how does it arise?

Answer 21

repeated vomiting over an extended period, loss of H+

Question 22

how do you distinguish between respiratory and metabolic acidosis/alkalosis

Answer 22

measurement of pH and partial pressures of gases in the blood, measure ARTERIAL PCO2, PO2

Question 23

if the change is metabolic in origin (acidosis or alkalosis) what indication would you be looking for?

Answer 23

both pH and HCO3- moving in the SAME direction

eg/ increase in pH and in HCO3- = alkalosis, decrease in pH and in HCO3- = acidosis

Question 24

if the change is respiratory in origin (acidosis or alkalosis) what indication would you be looking for?

Answer 24

pH and HCO3- moving in OPPOSITE direction
e.g. increase in pH, decrease in HCO3- = respiratory alkalosis
decrease in pH, increase in HCO3- = respiratory acidosis