what is the partial pressure of oxygen in blood? & what maintains this pressure?

Oxygen Transport

In the lungs, oxygen diffuses from alveolar air into the blood because the venous blood has a lower partial pressure. The oxygen dissolves in the blood. Only a small amount is carried as a physical solution (0.31 ml per 100 ml). The remainder of the oxygen is carried in chemical combination with the hemoglobin in red blood cells (erthrocytes).

from http://www.elmhurst.edu/~chm/vchembook/260acidbase...

Normal analysis results

Normal blood gas values are as follows:

 partial pressure of oxygen (PaO2): 75-100 mm Hg

from http://www.healthatoz.com/healthatoz/Atoz/ency/blo...

Arterial and venous blood have different partial pressure values the former being higher rthan the latter as trhe latter is the result of OXgen being drawn by tissues for consumption. The atmosphereic pressure anbd the Percentage of O2 in the atmosphere, The Respiratory rate, tidal volume, the Surface area of the lung (Almost the size of a football field if you really spread it out) and the bloof flow rate all determine the Partial pressure of O2 in Arteries and veins.

Arterial PaO2 is usually higer than 75 mm Hgand under normal atmospheric conditions in a healthy adult who is physiologically at res can go as high as 110 though it can be made to achieve higher values under laboratory atmosphereic conditions - higher atmosphereic pressure and higher o2 percentage in the environment or Physiological alterations such as hyperventialtion. Venous Partial pressure is ususlaly around 60 mm Hg and this depemnds on the amount of oxygen being drawn by the tissues and blood flow rate - sluggish flow means more o2 will be drawn and lower Po2. cell Respiratoiiry poisons - eg :- cyanide will result in higher venous P02 as Oxygen cannot be utilised by tisues and therefore it is not drawn from the vacular compartment.

Oxygen in blood is not under pressure, it is part of the blood.