At sea level, human body tissues are saturated with nitrogen at a partial pressure equal to:

At sea level, human body tissues become saturated with nitrogen at a partial pressure equal to the partial pressure of the gas in alveolar air. This is primarily due to the respiratory exchange that occurs in the lungs.

When we breathe, the air we inhale contains approximately 78% nitrogen. The partial pressure of any gas in a mixture is determined by multiplying the total atmospheric pressure by the percentage of that gas in the mixture. At sea level, the atmospheric pressure is about 1 atmosphere (or 760 mmHg), which means that the partial pressure of nitrogen in inhaled air will also be around 0.78 atmospheres, assuming ideal gas behavior.

Once the nitrogen enters the lungs and diffuses across the alveolar membrane into the bloodstream, the body will equilibrate with this partial pressure. This is crucial for understanding dive physiology and decompression, as the amount of nitrogen dissolved in body tissues is directly related to its partial pressure in the alveolar air and, thus, in the blood.

The other choices involve different pressure measurements that do not directly correlate with the saturation of nitrogen in body tissues. The absolute pressure of air at sea level accounts for the total atmospheric pressure but does not specifically reflect how gases are absorbed and utilized within the body