Your Body’s Microscopic “Trucks”
FIVE days ago it was a cell with a nucleus. But after an intense period of maturation and multiplication, with vigorous contractions, it expelled its nucleus. It is now a reticulocyte. What is that? It is an immature red blood cell, ready to enter your bloodstream. Two to four days from now, it will transform into a fully mature red blood cell.
This small cell is very much like a truck. Its means of carrying “cargo” is hemoglobin, a protein that transports oxygen. It has been estimated that during its four-month life, the “truck” will travel approximately 150 miles [250 km] throughout your body. There are about ten billion capillaries (minute blood vessels) in your body, with a combined length of twice the circumference of the earth. Trillions of erythrocytes (red blood cells) are needed to carry oxygen to all parts of the body.
This tiny “truck” is almost always on the move in your bloodstream. Its speed varies according to the circumstances. The cell reaches its top speed of about 50 inches [120 cm] per second when it is in the blood’s “superhighway” from the heart—the aorta. As the cell enters the body’s “side roads,” it gradually slows to an average speed of one hundredth of an inch [0.3 mm] per second in the terminal capillaries.
Where Blood Cells Come From
In normal adult humans, most blood cells are produced in the bone marrow. Every day, for every pound of body weight, your bone marrow produces one billion [2.5 billion] red cells, 400 million [1 billion] granulocytes (white cells), and one billion [2.5 billion] platelets. This compensates for the corresponding daily loss of cells. In a normal adult, millions of red blood cells are destroyed and replaced every second.
Now, to enter the bloodstream from the bone marrow, the immature red cell approaches the outer wall of small vessels (sinusoids) in the bone marrow, squeezes through a small aperture called a migration pore, and emerges into the blood. For about three days more, it will go on producing hemoglobin. But then, as a mature red blood cell, or erythrocyte, it will quit that activity.
The Systemic and Pulmonary Circulations
In the 17th century, doctors established that there are two types of blood circulation. In the systemic circulation, your body’s microscopic “trucks,” the red cells, set out from the heart to the body tissues. There they deliver oxygen and pick up refuse in the form of carbon dioxide. This process is called internal respiration. The red cells then return to the heart. In pulmonary circulation, the “trucks” are sent to the lungs. There they unload refuse and reload with oxygen. So pulmonary circulation allows your body to breathe.
When There Aren’t Enough Cells
Sometimes there are fewer red blood cells than normal. This is the condition doctors call anemia. It may have different causes, including (1) a defect in the production or maturation of red blood cells, (2) an increase in their destruction, and (3) major bleeding. Anemia may also result from chronic inflammation or tumors.
Problems can result when there is either too much or too little iron in the blood. When there is too little iron, the red cells cannot mature normally. As a result, the cells will be smaller and paler than usual. In many cases, treatment with iron corrects this defect. Sometimes the level of iron in the blood is too high. This can occur when damaged red cells rupture, releasing iron into the system. Progressively, all the body’s organs become poisoned. The poisoning of the heart is particularly serious. Patients suffering from this condition almost always succumb to chronic cardiac insufficiency.
Many books would be needed to explain all the work that blood cells do in your body, but it is evident that their marvelous complexity, only partially described here, exalts the wisdom of the One who designed and created life. Of the great and intelligent Creator, one of his ancient worshipers said: “By him we have life and move and exist.”—Acts 17:28.