Question

What are the partial pressures of O₂ and CO₂ within the alveolar air, arteries, and veins of mammals? How do these changes during a cardiorespiratory cycle?

Answer 1

Partial pressure- Pressure contributed by an individual gas in a mixture of gases is called partial pressure and represented as pO2 for oxygen and pCO2 for carbon-dioxide.

Partial pressure of O2 –

In Alveoli – 104 mm Hg

In Arteries- 95 mmHg

In Vein – 40 mmHg

At tissue – 40 mmHg

Partial pressure of Co2-

In Alveoli – 40 mm Hg

In Arteries- 40 mmHg

In Vein – 45 mmHg

At tissue – 45 mmHg

Cardiovascular cycle- During breathing process alveoli in the lungs are the prime site of exchange of gases but gaseous exchanges also occur between blood and tissue. Gas exchanged at all this site by simple diffusion based on the pressure gradient. Thickness of cell membrane involved in diffusion and solubility of gases are also some important factor that can affect the rate of diffusion.

Exchange of O2 at alveoli- Here pO2 is high (104) in alveoli compared to pO2 in deoxygenated blood (40) so oxygen diffuse into blood from the alveoli and fresh oxygenated blood travel through pulmonary vein to systemic arteries where pO2 is 95 mmHg and pCO2 is 40 mmHg.

In body tissue- Here pO2 is 40 which is less than pO2 of 95 in systemic arteries so oxygen get diffused in tissue and CO2 in tissue with pCO2 45 is greater than pCO2 of fresh blood (pCO2= 40) get diffused back in vein.

Exchange of CO2 at alveoli- in deoxygenated blood pCO2 (45) which is higher than pCO2 (40) of alveoli so CO2 diffused into alveoli.

As the solubility of CO2 is 20-52 times higher than O2, the amount of CO2 that can diffuse through the diffusion membrane per unit difference in partial pressure is much higher compared to that of O2. The diffusion layer made up of three layer thin squamous epithelium of alveoli, the endothelium of alveolar capillaries and basement substance between them. Hence the entire factor in body is favorable in for the diffusion of O2 from alveoli to tissue and of CO2 from tissue to alveoli.

Alveglos air (po 104 Afto=40 Pulmonary pulmonary rein artery To Heart Esystemic arteries | Cóxygenated blood veins (Dezsegerate blood) - Po=40 PCO2=45 PO2-95 marty pO2 = 40 mmity hok - Tissue

Hope this help you, good luck