Resp 4 - Gas transport and exchange Flashcards
State Dalton’s law
The partial pressure of a mixture of gases is equal to the sum of the partial pressures of the gases that make up the mixture.
Pgas mixture = Pgas1 + Pgas2 + … + Pgas n
State Fick’s law
Molecules diffuse from regions of high concentration to low concentration at a rate of diffusion is directly proportional to concentration gradient (P1-P2), the exchange surface area (A), the diffusion capacity (D) of the gas and inversely proportional to the thickness of the exchange surface (T).
Vgas= [ A x D x (P1-P2) ]/ T
State Henry’s law
At a constant temperature, the amount of a given gas that dissolves in a give type and amount of liquid is directly proportional to the partial pressure of the gas in equilibrium with the liquid.
State Boyle’s law
At a constant temperature, volume is inversely proportional to pressure.
Pgas proportional to 1/Vgas
State Charles’ law
At a constant pressure, volume is directly proportional to temperature.
Vgas proportional to Tgas
What is the proportion of O2, CO2 and N2 in the air?
O2 - 21%
CO2 - 0.04%
N2 - 78%
High altitude - same proportion of gases but smaller volumes
Describe how partial pressure of oxygen changes as it passes down the airways.
The partial pressure decreases from 21.3 kPa to 20 kPa to 13.5 kPa in the alveoli.
It is mixed to the air in the airways
How is the air modified in the airways?
Warmed
Humified (water pressure goes up to saturted to protect airways and improve conductivity)
Slowed
Mixed
How much oxygen can be dissolved in out bodies?
0.32mL/dL
= 16 mL/min
resting VO2 is approx 250mL/min so relying on oxygen alone is not viable so we have a more effective transport mechanism.
What is the normal oxygen consumption at rest?
250mL/min
What is the binding capacity of oxygen to haemoglobin?
1.34 mL/g
What is the solubility coefficient of oxygen in blood using mm Hg?
0.003 mL
What do we call a protein which changes structure depending on what it’s bound to, like haemoglobin?
Allosteric protein
–> cooperativity: the more O2 binds, the more prone it is to get other O2s
What change occurs in the middle of the haemoglobin tetramer when oxygen binds?
Oxygen binding changes the structure of the middle of the haemoglobin creating a binding site for 2,3-DPG (a glycolytic by-product) - 2,3-DPG production is reflective of metabolism and it binds to the haemoglobin and squeezes out the oxygen (lowers the affinity of haemoglobin for oxygen)
What is the name given to the phenomenon where oxygen binding to haemoglobin increases the affinity making more oxygen bind?
Cooperativity
What is Methaemoglobin?
It is the oxidised form of haemoglobin: Ferrous ion (Fe2+) transformed into ferric form fe3+. This does not bind to oxygen. Causes blue people and functional anaemia ie. normal HCL, PCV, but impaired O2 capacity
How is plotted an oxygen dissociation curve?
It is PO2 (kPa) against HbO2 saturation (%)
it shows that in the systemic circulation, O2 is more likely to unbind Hb (the smaller the O2 pressure, the more likely it unbinds (logic)) and in the pulmonary it is more likely to bind to O2 (on a wide range of partial pressures)
What is used to see if the ODC shifts right/left?
P50 (y axis) - partial pressure of oxygen when Hb sat is at 50%
What does a rightward shift of the ODC promote? a leftward shift? downward? upward?
- Rightward: promotes unloading - factors associated with exercise - Bohr effect - increased temp, acidosis, hypercapnia
- Leftward: promotes loading/affinity - all the contrary of rightward
- -> these can be seen with P50 - same total O2 in blood
- Downward: Anaemia - impaired oxygen carrying capacity
- Upward: Polycythaemia (abnormally high Hb conc) - increased oxygen-carrying capacity
- -> these will have the same P50 PO2 value, but the scale of the Hb is changed - squished - total O2 in blood is way lower - saturation doesn’t change
Downward AND leftwards - decreased capacity, increased affinity
When Hb binds to CO - less oxygen and less able to bind to it
What are the benefits of having a sigmoid ODC?
100% haemoglobin saturation can occur at a broad range of partial pressures - alveolar PO2
Large range and scope for unloading oxygen in the tissues - very high unloading capacity
What would the consequences be if the oxygen dissociation curve was linear?
A lower haemoglobin saturation would be achieved in the lungs when the partial pressure of oxygen in the lungs is at the lower end of normal. There is also reduced potential to unload oxygen at respiring tissues.
Describe the shape of the ODC of myoglobin and foetal haemoglobin and why this shape is needed for their function.
Myoglobin has much much greater affinity than HbA to ‘extract’ oxygen from circulating blood - it is the globin present in muscles - logic as they need great O2 supply
Foetal haemoglobin has greater affinity than adult to extract blood - logic because has to extract from mother’s blood in placenta
Why does the Hb saturation of the blood decrease from 100% at the respiratory exchange surface to 97% in the systemic circulation?
Because bronchial circulation drains into pulmonary vein
Why does O2 go in haemoglobin in red blood cells?
First diffuses into the blood - there the concentration of O2 is lower than in the RBC so it will diffuse quickly inside . When it comes in it occupies the final binding spot of haemoglobin - the blood doesn’t arrived deoxygenated it has a Hb sat of 75%.
