Explain why the gas values from the alveolar air to the blood change during pulmonary gas exchange. For example: Alveolar air for CO2 has a value of 40mmHg then when entering the blood shifts to 45mmHg
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Ans :
FROM ATMOSPHERIC AIR UPTO BLOOD
USING LAW OF PARTIAL PRESSURE OF GASES
1. In A Mixture Of gases (>2), not reacting with each other, each gas exerts pressure on Other gases - i.e PARTIAL Pressure.
2. Addition of all partial pressures is the total pressure.
3. Partial pressure of individual gas corresponds with its relative concentration in the mixture.
760mmHg Is Total Gas Pressure In Atmospheric Air, Out Of Which 80% is Contributed By Nitrogen. While, 20% is contributed by Oxygen.
PO2 = 20% Of 760mmHg
PO2 = 154 - 159mmHg At Sea Level.
2. PO2, IN THE DEAD SPACE (Inspired air)
. Humidification Occurs.
. Addition of water vapour occurs
PH₂0 = 47mm of Hg
Total Pressure = 760 mm Hg - 47mmHg = 713mm of Hg
PO2= 20% of 713 = 149 mm of Hg
3.PO2, IN THE ALVEOLI
-Oxygen conc Decreases
-Oxygen replaced by CO₂ gradually
→ PCO2 = 45mm of Hg
→PO2, in alveolar air= 149-45 = 104 mm of Hg
ALVEOLAR AIR EQUATION
PA0₂= [Fraction Of Inspired Air(Atmospheric Air Pressure- PH2O)] - [PACo₂]/Respiratory Quotient
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