The Earth’s atmosphere consists primarily of nitrogen, which makes up about 78% of the air we breathe. This abundant gas plays a unique role in our respiratory system, distinct from oxygen, which is actively utilized by the body. While we inhale a substantial amount of nitrogen with every breath, its journey and interaction within the body are quite specific and often misunderstood.
The Respiratory Path of Nitrogen
When air is inhaled, nitrogen gas (N2) travels through the respiratory passages and fills the alveoli, the tiny air sacs in the lungs. A small amount of nitrogen dissolves into the bloodstream, reaching equilibrium with the nitrogen already present in the body’s fluids and tissues. Unlike oxygen, which readily binds to hemoglobin and is transported for metabolic processes, nitrogen does not undergo chemical changes or significant absorption for biological use under normal atmospheric conditions. The vast majority of inhaled nitrogen remains in its gaseous form within the lungs and is simply exhaled, returning to the atmosphere.
Why Inhaled Nitrogen Remains Inert
The primary reason nitrogen gas is largely unreactive within the human body stems from its stable chemical structure. Each nitrogen molecule (N2) consists of two nitrogen atoms joined by a strong triple covalent bond. This triple bond requires a significant amount of energy to break, making the N2 molecule highly stable and unreactive under typical physiological conditions. The body’s enzymes and metabolic processes are not equipped to break this robust bond and directly utilize atmospheric nitrogen. In contrast, oxygen (O2) has a double bond, which is less stable and allows it to readily participate in biological reactions.
Nitrogen’s Essential Role in the Body
While nitrogen gas from the air is inert, nitrogen atoms are fundamental building blocks for life, being the fourth most abundant element in the human body by mass. Nitrogen is a core component of amino acids, which are the molecular units that form proteins, and it is also found in nucleic acids like DNA and RNA, which carry genetic information. The body obtains this essential nitrogen not from the air we breathe, but primarily through the consumption and digestion of nitrogen-rich foods. Proteins from nitrogen-rich foods provide the necessary nitrogen atoms for synthesizing new proteins and nucleic acids, crucial for growth, repair, and various bodily functions.
Nitrogen’s Behavior Under Pressure
Under increased atmospheric pressure, such as during scuba diving, nitrogen gas can interact more significantly with the body. According to Henry’s Law, as pressure increases, more nitrogen gas dissolves into the blood and body tissues. This increased dissolution of nitrogen can lead to conditions like nitrogen narcosis, where the dissolved nitrogen exerts an anesthetic effect on the central nervous system, impairing judgment and coordination.
A rapid decrease in pressure, such as a diver ascending too quickly, can cause the dissolved nitrogen to come out of solution and form bubbles within the blood and tissues. This phenomenon is known as decompression sickness, or “the bends.” These bubbles can cause pain in joints, neurological symptoms, and in severe cases, can be life-threatening by obstructing blood flow or damaging tissues. Proper ascent rates and decompression stops are necessary to allow nitrogen to be safely eliminated from the body, preventing these adverse effects.