Most people know that the tissues and cells of our body need oxygen. So it would not be a surprise question to ask, “Why is oxygen so important to the blood.” The real question is, “Why is blood so important to oxygen?”
In our bodies, blood plasma flows along as if it were a long highway winding past peripheral tissues on all sides. Oxygen and carbon dioxide do not have complete solubility in blood plasma. The limited solubility of these gases creates a problem for the surrounding tissues that need more oxygen, and produce more waste than the plasma can absorb and transport.
So for the plasma to be able to deliver enough oxygen to the tissues, and also be able to carry away the waste products (such as carbon dioxide and urea) that the tissues generate, an answer was needed.
Enter the red blood cells (RBCs). Red blood cells remove dissolved oxygen and carbon dioxide from the plasma inside blood vessels. The red blood cells take care of both the oxygen and the carbon dioxide. RBCs bind to oxygen and RBCs use the carbon dioxide to make compounds that are soluble.
The red blood cells bind to molecules of oxygen and build soluble compounds out of the waste products from tissues. The result, of these binding and building reactions, is that dissolved gases from the blood plasma are removed. Because dissolved gases are removed from the plasma, more gases are able to continue diffusion into the blood without ever reaching equilibrium.
The magic of red blood cells is that these reactions are both temporary and reversible. This allows RBCs to regulate the concentration of the blood plasma. When oxygen or carbon dioxide concentrations are high, then the RBCs remove more molecules. When plasma concentrations drop, RBCs contribute their stored reserves.
Oxygen transport is as important as the name implies. Every 100 ml of blood leaves the capillaries of the lungs carrying about 20 ml of oxygen. Of this 20 ml, only 1.5 percent is oxygen in solution. The rest is bound to hemoglobin (Hb) molecules. More specifically, it is bound to iron ions in the center of heme units.
A hemoglobin molecule is made of 4 heme globular protein subunits, each with a heme unit. So each hemoglobin molecule can bind four molecules of oxygen. The result is the formation of a oxyhemoglobin.
Each red blood cell has about 280 million molecules of hemoglobin. Times this by the four heme units, and the number of oxygen molecules that one red blood cell can carry is more than a billion. More than a billion oxygen molecules carried by one red blood cell!
It is a terrible thing to pick up the newspaper and read about an entire family that was killed in their sleep by a leaky furnace or space heater. The cause of death is carbon monoxide poisoning. Car exhausts, engines that burn petroleum, oil lamps, or fuel-fired space heaters all contain carbon monoxide (CO). Carbon monoxide competes with the oxygen molecules to bind on the heme sites. Sadly, carbon monoxide usually wins because it has a stronger affinity for hemoglobin than does oxygen.
The bond formed by CO and heme is extremely durable, so when it binds to the heme unit in a red blood cell it renders the heme unit completely inactive for respiratory purposes. If CO equals just 0.1 percent of the air inhaled, enough hemoglobin will be affected that death will occur without a doctor’s help!
Oxygen is one of the most important inorganic compounds found in our body. After all, oxygen is the atmospheric gas that is required for the important metabolic reactions that take place inside our cells. It is blood, however, that makes delivery of this life giving molecule possible. Blood is the liaison between oxygen and the cells of the body.
