The composition of the air inhaled and exhaled is thus grossly the same. Everything turns on an exchange of about 4 percent oxygen and 3 percent carbon dioxide.
The inhaled oxygen bonds to the iron atoms contained in the hemoglobin molecules that circulate in the arteries. Oxygen makes up about 20 percent of the volume of the arterial blood and 12 percent of the venous blood. The capacity of the blood to contain oxygen can easily double, but that happens very rarely. Carbon dioxide, transported mostly by blood plasma, makes up 50 percent of the plasma’s volume. Four percent of CO2 in circulation is freed through exhalation. The remaining amount is indispensable for the functioning of the internal respiration.
The issues linked to the ratio of iron in the blood introduce the concept of intermediary mechanisms. The more iron atoms in the blood, the more the blood can transport oxygen molecules. When the ratio of iron in the blood diminishes, the ratio of oxygen also inevitably diminishes. Respiration can then no longer respond to the demands of an increase in physiological activity, even when there is an increase of respiration and cardiac activity. Because the problem is not caused by the lungs or the heart but by a lack of iron, the organism soon finds itself in a crisis. If a physician gives a supplemental iron injection, and if the iron attaches well to the hemoglobin, the problem resolves immediately. The main causes of iron deficiency are poor absorption of iron by the body, inadequate daily intake of iron, pregnancy, blood loss due to heavy menstrual bleeding, or internal bleeding. Too much iron in the blood causes other problems.31
The equilibrium I have just described is important for the metabolic activity of the organism For example, it is influenced by the energy sources utilized by the activity of the organism (sugars, proteins, or fats). This is an example of interaction between respiratory behavior and the dynamics of metabolism The fatigue experienced by individuals who lack iron is an example of conscious awareness activated by physiological regulatory mechanisms of the organism