L16 (pk6) - Carriage of O2

Question 1

How is oxygen carried in the blood?

Answer 1

1. Physically dissolved in plasma solution (only this exerts a partial pressure)
2. Chemically bound to globular proteins (Hb in RBC)

Question 2

What is the formula for Henry’s law?

Answer 2

Dissolved O2 = P x solubility coefficient (a)

Question 3

What would the graph for O2 content and O2 partial pressure look like?

Answer 3

Linear

- At normal PaO2 (13kPa) there would be approx. (just under) 3ml/L

Question 4

What ppc are found in adult Hb?

Answer 4

• 2 alpha subunits

- 2 beta subunits

Question 5

What ppc are found in fetal Hb?

Answer 5

• 2 alpha subunits

- 2 gamma subunits

Question 6

Describe the structure of haemoglobin

Answer 6

• Each of the 4 haem groups binds to one of 4 ppc (globin) to make 1 Hb
• 4 chains
• 4 haem groups
• 1 haem group has 1 Fe2+ in middle of porphyrin ring

Question 7

What does the haemoglobin diss curve look like?

Answer 7

Sigmoidal
Y-axis = O2 content (ml/L)
X-axis = PO2 (kPa)

Question 8

What is oxygen content?

Answer 8

Quantity in a given sample of blood

- It is the amount of O2 combined with Hb PLUS the amount dissolved

Question 9

What is oxygen capacity?

Answer 9

The maximum quantity of O2 that can combine with Hb in a sample of blood (ie. content -dissolved)
- Dependent only upon the [Hb] and is independent of the partial pressure

Question 10

What is Hb saturation?

Answer 10

Ratio of quantity of O2 combined with Hb in a given sample to the O2 capacity of that sample
- Expressed as a %

Question 11

What equation can be used to determine oxygen capacity?

Answer 11

[Hb] x 1.34 (ml/O2/g/Hb)

Question 12

Where/ what is the ‘association’ part of the Hb dissociation curve?

Answer 12

• Flat part of curve (after diss)
• Part of curve ensures almost complete loading of Hb despite potential small fluctuations in level of PO2 in lungs, e.g. still 90% saturation at 8kPa PO2

Question 13

Where/ what is the ‘dissociation’ part of the Hb dissociation curve?

Answer 13

• Steepest part of curve (before assoc)
• Ensurse adequate delivery of O2 to tissues whilst still maintaining arterial PO2 levels high (important for diffusion), e.g. 60% desat from 8-3kPa PO2

Question 14

What causes the Hb dissociation curve to shift to the RIGHT?

Answer 14

1. Increasing PCO2 [BOHR EFFECT]
2. Decreasing pH [BOHR EFFECT]
3. Increasing temperature
4. Increasing 2,3-DPG concentration

Question 15

What causes the Hb dissociation curve to shift to the LEFT?

Answer 15

1. Decreasing PCO2 [BOHR EFFECT]
2. Increasing pH [BOHR EFFECT]
3. Decreasing temperature
4. Decreasing 2,3-DPG concentration