Oxygen and Carbon Dioxide Transport

Question 1

What is haemoglobin? What does it become when it takes up oxygen?

Answer 1

protein RBCs, oxyhaemoglobin

Question 2

What is the structure of haemoglobin?

Answer 2

4 subunits, each unit has a polypeptide chain and a haem group containing an iron atom (Fe2+) which attracts and holds O2: affinity for O2

Question 3

What is dissociation?

Answer 3

when oxyhaemoglobin releases the O2 for the cells for aerobic respiration

Question 4

How is oxygen measured?

Answer 4

amount of O2 = relative pressure that it contributes to a mixture of gases: partial pressure/pO2 or oxygen tension (kPa)

Question 5

How do describe the take up of oxygen by haemoglobin on a graph?

Answer 5

S-shaped curve, oxyhaemoglobin dissociation curve, low O2 tension = haemoglobin doesn’t readily take up O2 mols, haem group in middle of mol so hard for O2 to associate with it = low saturation level

Question 6

What happens to the diffusion gradient as oxygen tension rises?

Answer 6

increases, eventually one O2 mol diffuses into haemoglobin and associated with a haem group

Question 7

What is the change of shape of a haemoglobin mol called when the first oxygen mol associates with a haem group?

Answer 7

Conformational change: allows more O2 mols to diffuse into haemoglobin = steepness of curve as O2 tension rises

Question 8

What happens once the haemoglobin contains 3 oxygen mols?

Answer 8

more difficult for the 4th one to diffuse in and associate, difficult to get 100% O2 saturation so curve levels off as graph approaches 100% saturation

Question 9

How does fetal haemoglobin differ from adult haemoglobin? Why is this?

Answer 9

Higher affinity for O2, must absorb O2 from fluid in mother’s blood which lowers O2 tension which makes maternal haemoglobin release O2 = fetal curve left of adult curve

Question 10

What is the Bohr shift?

Answer 10

change in shape of oxyhaemoglobin dissociation curve when CO2 present - causes release of O2 more readily

Question 11

How is carbon dioxide transported in the blood? (3 ways)

Answer 11

5% dissolved in plasma, 10% combined with haemoglobin to form carbaminohaemoglobin, 85% transported in form of hydrogencarbonate ions (HCO3-)

Question 12

What happens when some of the carbon dioxide in the blood enters red blood cells?

Answer 12

Combines with water to weak acid: carbonic acid, catalysed by carbonic anhydrase

Question 13

What happens to the carbonic acid?

Answer 13

dissociates to release H ions and hydrogencarbonate ions

Question 14

What happens to the hydrogencarbonate ions in the red blood cells?

Answer 14

diffuse out into plasma, charge inside RBC maintained by chloride ion movement from plasma into red blood cell: chloride shift

Question 15

What do the hydrogen ions in the red blood cell do?

Answer 15

cause contents to become very acidic, to prevent this H ions are taken up by haemoglobin (acting as a buffer) = haemoglobinic acid

Question 16

What causes oxyhaemoglobin to dissociate and release oxygen into respiring tissues?

Answer 16

O2 tension of respiring tissues is lower than in the lungs because O2 has been used in respiration

Question 17

What do the hydrogen ion released from the dissociation of carbonic acid do?

Answer 17

compete for space taken up by O2 on the haemoglobin mol, when CO2 present, H ions displace the O2 on the haemoglobin, so oxyhaemoglobin releases more O2 to tissues

Question 18

What does the Bohr shift do the oxyhaemoglobin dissociation curve?

Answer 18

more CO2 present haemoglobin = less saturated with O2 so curve shifts downwards and to the right