3- Gas Transport And Exchange Flashcards
What are the 5 gas laws
DFCBH
Dalton: Pressure of a gas mixture is equal to the sum (Σ) of the partial pressures (P) of gases in that mixture
Fick: molecules diffuse from regions of high concentration to low concentration at a rate proportional to the CONCENTRATION GRADIENT, the exchange SURFACE AREA and the DIFFUSION CAPACITY of the gas, and inversely proportional to the THICKNESS of the exchange surface
Charles:v=kT
Boyle: P=k/V
Henry: 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
Differentiate between the structure and function of gas-binding proteins; adult haemoglobin, foetal haemoglobin, methaemoglobin and myoglobin
- HbA: 4 monomers (2α2β); haem contains Fe2+; each binds 4O2; sigmoid shaped ODC; binds 2,3-DPG
- HbF: 4 monomers (2α2γ); haem contains Fe2+; each binds 4O2; greater affinity than HbA
- MetHb: same as HbA but Fe2+ is oxidised to Fe3+; does not bind O2; occurs naturally <1%
- Mb: One monomer; haem contains Fe2+; storage protein found in muscle; hyperbolic ODC
What happens to air as it passes through the lungs
- In dry air, you have 21.3 kPa of oxygen
- Through the conducting airways there is a slight reduction in PO2 and an increase in PH20
- The increase in PH20 is because the dry air gets warmed, humidified, slowed and mixed as it passes down the respiratory tree
- By the time you get to the respiratory airways, you have about 13.5 kPa of oxygen
What is 2,3- DPG
When ATP is being produced in large amounts, more 2,3-DPG is produced so it is reflective of metabolism
• When metabolism is higher you want more oxygen so the 2,3-DPG will bind to the haemoglobin and squeeze OUT the oxygen so there is more available for the respiring tissue
• 2,3-DPG DECREASES the affinity of haemoglobin for oxygen
What can cause the ODC to shift right (less o2 affinity)
Increase in temperature
Acidosis (due to production of lactic acid and excess CO2)
Hypercapnia (elevated CO2 because there is more cellular metabolism) Increase in 2,3-DPG
What can cause ODC to shift left - greater o2 affinity
Decrease in temperature Alkalosis
Hypocapnia
Decrease in 2,3-DPG
What causes theODC to move up or down
Anaemia shifts down
Polycythaemia up
What does CO poisoning do to the ODC
Downward and Leftward Shift
Why When the blood reaches the tissues will it be around 97% saturated not 100%
• THE BLOOD WILL BE DILUTED BY THE BRONCHIAL CIRCULATION
• The pulmonary system has two circulations - it has it’s own blood supply to
keep it alive and it has the pulmonary blood supply for oxygenation of blood
• The circulation keeping the lung tissue alive drains back into the pulmonary
circulation before returning to the left atrium
How is CO2 transported
Carbaminohaemooglobin
H2CO3
HCO3- in plasma mostly
What is the pulmonary transit time
The pulmonary transit time is around 0.75 s - the blood cells are only in contact with the respiratory membrane for this short time
• By 0.25 s, all of the gas exchange is complete (at rest)
• When exercising, cardiac output increases and pulmonary blood flow increases
and the lines get stretched rightwards - however, there is still time to
reoxygenate the blood
• CO2 is much more willing to cross through the membranes so it exchanges
much faster
What is the Haldane Effect
Haldane Effect = describes how the amount of carbon dioxide that binds to the amine end of the haemoglobin protein chains changes depending on how much oxygen is bound - this is another allosteric behaviour
• Usually when the oxygen saturation is 100% (immediately after the alveoli) we don’t want to be binding CO2 and so at this point, carbon dioxide will not bind to the amine end of the proteins. But will bind at tissues
Describe perfusion and ventilation in the 3 lung zones
od perfuses the apex of the lung because of the RESISTANCE OF GRAVITY
• Regarding ALVEOLI - there is a similar relationship - there is better ventilation at the BOTTOM compared to the top
What is resting 02 consumption
250mL/min
What is normal arterial O2 conc
20ml/Dl
