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Hey, you have a good grip on gas exchange occuring. Could you stepwise explain what exactly and how the pressures change in Lung to blood and Tissue to blood as O2 moves in and out.

Seem to have a problem with that
Can you confirm my thought process here?

So
Lung to Tissue
-What drives diffusion in normal Lung alveoli is Pressure gradient. (high to low)
-PAo2 is 100 and PVo2 (venous blood) is 40
now this is where i am having problems with

-When O2 enter the blood, some of it dissolves in blood (is this what creates the Pa02 or some dissolves and other molecules are undissolves and as the undissolved O2 (is this Po2) increase in amount the O2 starts moving into RBC and bind to Hb.
Or is it that once O2 dissolves in blodd and when the blood capacity is maxed the O2 now moves into Hb and that is what determines the PaO2 in blood.

I am basically having a difficult time with this Pao2 and what creates it in the first place

What are the steps at the tissue level? What makes O2 come of the Hb originally? Meaning what causes the Po2 to change so that O2 can be unloaded?

Your clarification would be greatly appreciated

I read this again and I think i understand it now, but would appreciate some confirmation
thanks

PaO2 is the oxygen dissolved in plasma not RBC,and not in Hb,and that's way it remains normal in CO toxicity.
blood O2 content is the O2 in the Hb plus the PaO2(which is very small fraction of the O2 content)

PaO2 , is a partial pressure of the Oxygen

molecules in blood that's all I can tell

you & how I get it .. exactly like when we

have a partial pressure of O2 in alveolar

air or in room air .
the process is ... when capillary blood

comes in contact with alveolar air , there

will be a kind of equilibrium between alveolar

air & between cap. blood cOzing the Pao2 to

rise , this is the first step .
then this rise in pao2, will cause the O2

Hb to rise first ,, Load Hb ..when Hb is

100% loaded ( no matter wt Hb concentration

we have ..O2 then shifts to get dissolved

in blood ( in fuild of blood )which

accounts only small fraction for total O2

content of blood .
Pao2 affect the content by affecting the Hb

satuartion ..& you can see that 100 Pao2

will coz almost 100% saturation i.e all 4

Molecules of Hb/RBC r loaded & this will

decrease with decreament of Pao2 ..
now you can calculate the total contect by

adding what Hb carry & what fluid carrys

Hb carrys 1.34 gm of O2 /one gram of Hb
1.34 * Hb concentration *Hb saturation

will give us the O2 with Hb

Dissovled = pao2 * 0.003 = very small

fraction & will not help to optimize

delivery if there is a defect in O2 Hb .

in Co poisoning ..well what happenes is the

change of Hb affinity ( which not related

to pao2 ) ..so what ever pao2 will be, Hb

sites will be first occupied by Co

molecules ..& the rest of Hb mol. will have

a very high affinity to o2 making unloading

at tissue level very difficult ..& of

course the dissovled pao2 willnot get

changed & will be nothelpful at all becz essentially it only contibute to 2% of total .
Hope I could help .
GL Ben

just one thing added .. I reviewed Goljian , you r rt , he says that Pa02 is the dissolved po2 , but itis ... on Kaplan & BRS .. said other thing like what I explained above ..
also one leak ..& sorry for that .. o2 solubility is 0.03