Question

What could account for the small difference in pO2 between the pulmonary capillaries and systemic arterial blood?

Answer 1

• partial pressure is the pressure exerted by a specific gas in a mixture of gases and the pressure exerted by each individual gas is independent of the other. All the gas can passively diffuse from th area of high conccentration to an area of low concentration
• partial pressure is calculted by multiplying concentration of the given gas with total pressure
• pO2 of the dry air = 0.2094 x 760 = 159mmHg
• oxygen is transported across by two ways

1. physically dissolved oxygen - this type of transpot is occuring in th respiratory membrane ie in the pulmonary capillaries , where it dissolve on the basis of solubility coefficient and partial pressure. 0,003ml of oxygen is dissolved in 100ml of plasma at a pO2 of 1mmHg. At pO2 of 100mmHg in the arterial blood , 0.3ml of oxygen get dissolves in each 100ml of blood
2. chemical combination with Hb - O2 after enter into plasma get into RBC, in it carried as association with Hb ie, each Hb carry 4 mplocules of oxygenthe affinity of oxygen binding increase with increase in addition ie the first oxygen have less affinity than the fourth oxygen. At a pO2 100mmhg (arterial blood) 97.5% Hb get saturated with oxygen and the maximum oxygen carry by 1g of Hb is 1.34ml

• the partial pressure of O2 in the capillary is reduced by cooling effect ie , the water vapour is added to it causing reduction in the partial pressure of oxygen along with other gases but te reduction is more profound in case of O2 . this cause diffusion of O2 into the pulmonary capillaries
• But in case of artery the demand of O2 by various tissues are different based on their metabolic processes causing the reduced diffusion of O2