Composition of blood
Blood is composed of red cells, white cells, platelets and plasma. Red cells carry oxygen and carbon dioxide. White cells are our defense system. Platelets prevent bleeding
Plasma: blood without the cells
Plasma is composed of water, salts, sugars and various proteins, such as lipoproteins -the cholesterol “taxis”- and antibodies, the proteins which protect us from infections.
By analogy with the cholesterol “taxis”, the red blood cells are the oxygen carriers like littles boat.
Their red color is due to the fact they contain hemoglobin. This protein contains iron which acts like a magnet on oxygen.
Preference for oxygen
The red blood cells prefer the company of oxygen to that of the carbon dioxide (CO2). When they circulate in the lungs where there is much oxygen available, the red blood cells release their carbon dioxide content and reload with oxygen to supply the organs and muscles of the body.
At the organ and muscle level, the red blood cells are in a zone low in oxygen and rich in carbon dioxide. They release their oxygen cargo and reload carbon dioxide.
The transport of oxygen to organs and muscles and carbon dioxide to the lungs is vital function!
Pump and plumbing
This transport could not be carried out without a pump to ensure circulation through a network of conduits and pipes. This pump is the heart.
These conduits, the blood vessels, put end to end, would create a network of almost 100,000 kilometers.
As of the 14th day of foetal life, the heart and the red blood cells begin their work in this immense network.