Each of our blood cells can live only a particular length of time, and so the body must continuously replace worn-out cells. Blood cells are formed in the bone marrow.
The cellular portion of our blood is composed of red blood cells, white blood cells, and platelets.
Red blood cells live about 120 days. Red Blood Cells (RBCs), also known as erythrocytes, serve to transport oxygen (O2) around the body. They contain hemoglobin, which carries the O2 and exchanges this for carbon dioxide (CO2) released by the processes of metabolism from the cells.
White Blood Cells (WBCs), also known as leukocytes, mainly serve to protect the body from foreign material such as bacteria. There are different types of WBCs: neutrophils, basophils, eosinophils, and lymphocytes. eosinophils are primarily involved with allergic reactions, while neutrophils are the main infection fighters. Lymphocytes serve to protect against infection and also play a role in long-term immunity. The life span of the many types of infection- fighting white blood cells varies greatly. For example, neutrophils live only a few hours, dying soon after they ingest foreign material (phagocytosis). Another type of white blood cell, the lymphocytes, live many years, thus providing long-term immunity against certain diseases.
The life-span of platelets about 10 days. Platelets are the primary clotting elements of blood. When blood vessels walls are injured, platelets adhere to the site of injury to form a clot. Too few platelets, however, leads to bleeding, too many can result in inappropriate blood clot formation.
Last Editorial Review: 7/23/2002