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 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 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 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 red cells, 400 million granulocytes (white cells), and one billion platelets. This compensates for  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 the small vessels (sinusoids) in the bone marrow, squeezes through a small aperture 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. 

Next time: YOUR BODY'S MICROSCOPIC "TRUCKS"/ The Systemic and Pulmonary Circulations 

From the jw.org publications