Blood cells are born in the bone marrow and are delivered into the bloodstream to begin work.  Blood cells only live a limited time in the blood.  Old blood cells are destroyed by a type of cell called a macrophage.  Macrophages are the trash collectors of the body and are, in fact, blood cells themselves.  Even old macrophages are "eaten" by macrophages.  Some macrophages migrate to certain parts of the body and are given a new name.  For example, macrophages that enter the liver are renamed "Kupferr cells" and macrophages in the connective tissues are called "histiocytes."

How long do blood cells live?

On average...

• Red blood cells - 120 days
• White blood cells - about 1 - 3 days
• Platelets - about 1 - 2 weeks

What are macrophages?

Macrophages are a specialized form of white blood cell which serve as the body's trash collectors.  The term "macrophage" comes from the Latin roots "macro" which means large, and "phage" which means eaters.  Macrophages are "big eaters!"  Macrophages consume and destroy germs, old blood cells, old or damaged tissue cells, and other various waste products found in the body.

Macrophages in the body tissues are sometimes given different names based on where they are located.

How is a red blood cell recycled?

Red blood cells live to be about 120 days.  When they reach this age, the cell shrinks in size and becomes easily damaged.  The cell is filtered out of the blood by macrophages in the spleen (and to a lesser degree by macrophages in other parts of the body). 

Iron in the red blood cells is removed and delivered back to the bone marrow on iron-carrying proteins.  Excess iron can be stored in the liver. 

Hemoglobin is made of two major parts - 1) the protein portion which is broken down into amino acids, and 2) the heme portion which is converted into bilirubin. Bilirubin must first be converted into a form that can be excreted by the liver in bile.  This process is called "conjugation."  Conjugated bilirubin is excreted into the intestines in bile.  Bile is what gives stool it's brown color.  If this process is disrupted, excess bilirubin can collect in the blood and cause the skin to appear yellow (jaundice).

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