Lecture 19 - Blood gas transport

Question 1

Gas percentage in the atmosphere

Answer 1

Nitrogen: 78.6%
Oxygen: 20.9%
Carbon dioxide: 0.04%
Water vapour: 0.46%

Question 2

Gas percentage in the atmosphere

Answer 2

Nitrogen: 75.4%
Oxygen: 13.2%
Carbon dioxide: 5.2%
Water vapour: 6.2%

Question 3

Dalton’s law of partial pressure: what is it and how is it worked out

Answer 3

“the total pressure exerted by a mixture of gases is the sum of the pressures exerted independently by each gas in the mixture”

Units are millimetres of mercury

% in atmosphere x atmospheric pressure

Question 4

Henry’s law of pressure

Answer 4

“amount of gas that dissolves in water is determined by its solubility in water and its partial pressure in the air”

At equilibrium, the amount of dissolved gas in a solution is proportional to its partial pressure

Question 5

Solubility in capillaries

Answer 5

Although it is dependent on partial pressure, solubility is also quite important:

CO₂ = 5.2% in alveoli, but = 26ml/L
O₂ = 13.2% in alveoli, but = 3ml/L

Question 6

How does the blood transport oxygen if solubility is so low?

Answer 6

Haemoglobin: 97% of oxygen in plasma is in haemoglobin, composed of 4 globins (2α and 2β subunits) and 4 haem non-protein groups

Question 7

What affects the binding of oxygen to haemoglobin?

Answer 7

• Pressure of O₂ (higher, saturation higher)
• Blood pH (lower, more O₂ given to tissues)
• Temperature (higher, more O₂ given to tissues)
• State of O2 binding of the Hb molecule

Question 8

Carboxyhaemoglobin

Answer 8

CO binds tighter than O₂ (200x greater) and it dramatically reduces the ability of O₂ to bind to Hb

Question 9

Methaemoglobin

Answer 9

Forms when Fe²⁺ is oxidised to Fe³⁺ by drugs etc.

This haemoglobin is unable to carry O₂ but it is slowly converted back to normal over time

Question 10

Fetal haemoglobin

Answer 10

Haemoglobin composed of 2α and 2γ globin subunits, causing it to have a higher affinity for O₂

Important in transferring O₂ across the placenta

Question 11

Three ways that carbon dioxide is transported through the plasma

Answer 11

Carbonic acid formation, H₂CO₃⁻ and then transport through plasma as bicarbonate ion HCO₃⁻ (70%)

Haemoglobin: carbaminohaemoglobin (23%)

Dissolving in plasma (7%)

Question 12

Carbonic acid formation

Answer 12

CO₂ + H₂O + carbonic anhydrase -> H₂CO₃

H₂CO₃ then dissociates into HCO₃⁻ + H⁺

This process occurs in the red blood cell and HCO₃⁻ is removed through a chloride shift (Cl⁻ moving in and HCO₃⁻ moving out of the cell simultaneously)

Question 13

Why isn’t blood acidic despite the large production of H⁺?

Answer 13

Imidazole groups of histidine are in haemoglobin and they bind to H⁺, turning NH into NH₂⁺

Deoxygenated haemoglobin has the strongest affinity for H⁺