Lecture 4.1: Oxygen in Blood

Question 1

What gases are carried in the blood and where to?

Answer 1

• Blood carries oxygen to tissues
• Carbon dioxide away from tissues

Question 2

How many mmol of oxygen do we need per minute?

Answer 2

12

Question 3

Which pigment in the blood binds reversibly to oxygen? What is this process called?

Answer 3

• Haemoglobin
• This is oxygenation not oxidation

Question 4

How are dissociation curves normally expressed?

Answer 4

• As percentage of amount of oxygen bound at saturation
• Are independent of pigment concentration

Question 5

What do Dissociation Curves tell you?

Answer 5

• Tells you how much oxygen will be bound or given up
• When blood is moved from one pO2 to another

Question 6

Application of Dissociation Curves

Answer 6

• Work out the difference in fractional saturations between the two pO2s
• Multiply it by the amount bound at full saturation
• Tells you how much oxygen is taken or given up

Question 7

Structure of Haemoglobin?

Answer 7

• A tetramer - 2 alpha & 2 beta subunits
• Each subunit has one haem + globin

Question 8

Tense vs Relaxed Haemoglobin

Answer 8

• Tense haemoglobin (T-state) is uptight and does not bind oxygen well
• Relaxed haemoglobin (R-state) is laid back and loves to bind oxygen

Question 9

When does haemoglobin get ‘Tense’?

Answer 9

• When pO2 is low
• So it is hard to bind the first oxygen as most molecules are in the tense form

Question 10

What is the shape of the Haemoglobin Dissociation Curve?

Answer 10

Sigmoidal

Question 11

At what kPa is Haemoglobin saturated?

Answer 11

Above 8.5kPa

Question 12

At what kPa is Haemoglobin virtually unsaturated?

Answer 12

Below 1.0kPa

Question 13

At what kPa is Haemoglobin half saturated?

Answer 13

Around 3.5-4kPa

Question 14

How much Hb is there in blood in mmol/L and in g/L?

Answer 14

• 2.2 mmol/L
• 140 g/L

Question 15

How many mmol/L of oxygen in 1 molecule of Hb?

Answer 15

• Each molecule binds 4 oxygen = 8.8 mmol/L

Question 16

What is the lowest possible kPa of oxygen in (most) tissues?

Answer 16

• Must be high enough to drive oxygen out to cells
• Cannot fall below 3 kPa in most tissues

Question 17

What does the mood of Hb depend on? When is it in the R-State?

Answer 17

• The mood of haemoglobin also depends on pH
• The molecule is more relaxed in alkaline conditions
• More tense in acid

Question 18

What is the Bohr Shift?

Answer 18

• Describes haemoglobin’s lower affinity for oxygen secondary to increases in
the partial pressure of carbon dioxide and/or decreased blood pH
• Higher temperature has similar effect

Question 19

What percentage of bound oxygen is given up?

Answer 19

c.70%