Oxygen Transport in the Blood

Question 1

Is O2 soluble in water?

Answer 1

Not very

Question 2

What are respiratory pigments?

Answer 2

A coloured compound that is capable of reversible binding with oxygen at high oxygen concentrations & releasing it at low oxygen concentrations

Question 3

What 4 groups do respiratory pigments fall into?

Answer 3

Haemerythrins
Haemocyanins
Chlorocruorins
Haemoglobins

Question 4

What is the structure of haemoglobin?

Answer 4

• 4 haeme groups (porphyrin rings), each with an iron (Fe2+) atom at the centre
• Each haeme group is surrounded by a protein chain (globin)
• Oxygen is transported bound to iron atom at centre of haeme

Question 5

How many oxygen molecules can each haemoglobin molecule carry?

Answer 5

4

Question 6

What determines whether haemoglobin will bind oxygen or release it?

Answer 6

PO2
Haemoglobin will bind oxygen at high PO2
Hb + O2 —> HbO2
Haemoglobin will release oxygen at low PO2
Hb + O2 <— HbO2

Question 7

What is the PO2 in the atmosphere at sea level?

Answer 7

160 mmHg

Question 8

Where does Hb load and offload O2 in the body?

Answer 8

Loads O2 in lungs
Offloads O2 in tissues

Question 9

What model shows the saturation of haemoglobin at different partial pressures?

Answer 9

The oxygen disassociation curve

Question 10

Describe oxygen dissociation curve

Answer 10

• Pigments that load fully only at high PO2 have
  low affinities whereas those that are saturated
  at low PO2 have high affinities (i.e. as the curve
  shifts to the right, affinity decreases)
• A steeper curve shows a higher affinity for O2 (loads it at lower PO2)
• Fish have steeper curve than mammal as water has a lower PO2 than air

Question 11

Name 4 physical factors that affect the
oxygen dissociation curve

Answer 11

• CO2 and pH
• Temperature
• Inorganic ions
• Organophosphates

Question 12

How does CO2 & pH affect the oxygen dissociation curve?

Answer 12

• Increase in PCO2 in the blood results in a
  decrease in the affinity of haemoglobin, shifting
  the oxygen dissociation curve to the right
• This effect is known as the Bohr shift or Bohr effect
• Hb shifts to a lower affinity as it
  enters tissues where the PCO2 is high &
  reverts to normal when it returns to lungs
• Low affinity in tissues promotes
  release of O2 & change back promotes
  O2 loading in lungs

Question 13

What is the Bohr effect?

Answer 13

Increase in PCO2 in the blood results in a
decrease in the affinity of haemoglobin, shifting
the oxygen dissociation curve to the right

Question 14

How does body size affect the oxygen dissociation curve?

Answer 14

• Small animals have higher mass-specific
  metabolic rates than do large animals
• They have haemoglobin with a lower affinity for O2, which facilitates the release of oxygen to the
  tissues

Question 15

How does temperature affect the oxygen dissociation curve?

Answer 15

• Increase in temperature weakens the Hb-O2
  bond & haemoglobin then gives up oxygen
  more readily (the curve shifts to the right)

Question 16

Where are organophosphates found?

Answer 16

• RBC of vertebrates

Question 17

What can organophosphates affect?

Answer 17

O2 binding properties of Hb

Question 18

What are the most important organophosphates?

Answer 18

• Mammals = DPG
• Birds = IPP
• Fish/amphibians/reptiles = ATP/GTP

Question 19

How do higher levels of DPG affect the dissociation curve?

Answer 19

• Shift it to the right
• Reduced affinity
• O2 released at relatively high PO2

Question 20

What mammals experience high levels of DPG?

Answer 20

Those that live at high altitudes, where ambient PO2 is less

Question 21

Give an example of an animal that has respiratory pigments with a high O2 affinity but live in environments where PO2 is low

Answer 21

Prairie dogs