04 Gas Transport & Exchange

Question 1

Describe Fick’s Law

Answer 1

V Gas = 𝐴/𝑇∙𝐷∙[𝑃1−𝑃2]

Molecules diffuse from regions of high concentration to low concentration at a rate proportional to the concentration gradient (P1-P2), the exchange surface area (A) and the diffusion capacity (D) of the gas, and inversely proportional to the thickness of the exchange surface (T)

Question 2

Describe Dalton’s law

Answer 2

Pressure of a gas mixture is equal to the sum (Σ) of the partial pressures (P) of gases in that mixture (partial pressure)

Question 3

Describe Henry’s law

Answer 3

𝐶(𝐷 𝐺𝑎𝑠)=𝑎(𝐺𝑎𝑠) ∙ 𝑃(𝐺𝑎𝑠)
At a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid (how soluble the gas is)

Question 4

Describe Boyle’s law

Answer 4

At a constant temperature, the volume of a gas is inversely proportional to the pressure of that gas

Question 5

Describe Charle’s law

Answer 5

At a constant pressure, the volume of a gas is proportional to the temperature of that gas

Question 6

How can the composition of inspired air be altered

Answer 6

Smoke from fire
O2 therapy
High altitude

Question 7

Describe the changes to air as it passes from the atmosphere to the lungs

Answer 7

Warmed
Humidified
Mixed
Slowed

Question 8

Describe the changes of to the composition of air from atmosphere to conducting airway to respiratory airway in terms of O2, CO2 and H2O

Answer 8

Atmosphere:
- O2: 21 kPa
- H2O: 0
- CO2: 0
Conducting airway:
- O2: 20 kPa
- H2O: 6.3 kPa
- CO2: 0
Respiratory airway
- O2: 13.5 kPa
- H2O: 6.3 kPa
- CO2: 5.3 kPa

Question 9

Describe the structure of haemoglobin molecule

Answer 9

Monomer haemoglobin consists of a ferrous iron (Fe2+) at the centre of tetrapyrrole porphyrin ring connected to globin covalently at the proximal histamine residue. 4 haemoglobin monomers form a tetramer which is a Hb molecule capable of carrying 4 oxygen molecules

Question 10

Compare the structure between haemoglobin and foetal haemoglobin

Answer 10

Haemoglobin:
- HbA (2a and 2b)
- HbA2 (2a and 2d)
Foetal haemoglobin
- HbF (2a and 2g)

Question 11

Describe the properties of haemoglobin molecule when binding oxygen

Answer 11

Allosteric protein which allows cooperative binding (increasing affinity as oxygen occupies Hb molecule)

Question 12

Describe the condition methaemoglobin

Answer 12

It is when ferrous iron become oxidised to ferric iron (Fe3+) which cannot bind oxygen and cause functional anaemia (i.e. normal Hct, normal PCV, but impaired O2 capacity)

This can be due to excess oxidative stress (nitrites) or lack of NADH dependent methaemoglobin reductase

Question 13

Describe the effect of oxygen dissociation curve

Answer 13

This gives RBC the characteristics that:

• at high O2 content (alveoli), changes in oxygen content do not significantly change the oxygen saturation
• at low O2 content (respiring tissues), changes in oxygen content results in significant O2 unloading

Question 14

State the factors that can cause rightward shift of ODC

Answer 14

Hypercapnia
2,3 DPG (glycolytic by-product)
Low pH
Increased temperature

Question 15

What can cause upward and downward shift of ODC

Answer 15

Upward: polycythaemia (high RBC)
Downward: anaemia

Question 16

What are the effects of carbon monoxide on ODC

Answer 16

Leftward and downward shift as carbon monoxide has higher affinity binding to Hb than oxygen (therefore lower oxygen carrying ability) and it does not readily unload

Question 17

Describe the significance of foatal haemoglobin on ODC

Answer 17

It is shifted leftward relative to adult Hb. This indicates higher affinity to oxygen. Therefore the foetus can extract oxygen molecules from the mother’s haemoglobin

Question 18

Describe the structure of myoglobin and the significance of its ODC

Answer 18

One monomer; haem contains Fe2+; storage protein found in muscle; hyperbolic ODC

It has extremely high oxygen loading ability to extract oxygen from adult haemoglobin

Question 19

Describe the oxygen flux process with regard to the changes in oxygen content as blood passes respiring tissues

Answer 19

Oxygen flux:

• 5 ml/dl (Oxygen content from 20 ml/dl to 15 ml/dl)
• 250 ml of oxygen / min

PO2 from 12.7 to 5.3 kPa
Haemoglobin saturation 97% to 75%

Question 20

State the function of red blood cells

Answer 20

Oxygen transport
CO2 transport
Buffers acid

As CO2 binds to haemoglobin, it forms carbaminohaemoglobin which is negatively charged and has an effect on binding protons to neutralise blood. This is also strengthened by AE1 transporter (bicarbonate into blood and Cl- into haemoglobin)

Question 21

Describe the CO2 flux

Answer 21

+ 4 ml/dl (from 48 ml/dl to 52 ml/dl)
+ 200 ml of CO2 / min

PvCO2 from 5.3 to 6.3 kPa

Question 22

State the pulmonary transit time and time taken for complete gas exchange for oxygen

Answer 22

0.75s and 0.25s

Question 23

What is the idea V/Q

Answer 23

0.8

Question 24

Describe Haldane’s effect

Answer 24

• Hb binding O2 promotes CO2 unloading in the lungs

- Deoxyhaemoglobin will more readily form carbaminohaemoglobin and unload O2