Anemia - Introduction

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Red blood cells typically circulate for about 120 days before they are broken down in the spleen. Most of the iron used in hemoglobin can be recycled from there and reused.

Structure and Shape of Red Blood Cells

Red blood cells -- the erythrocytes -- are extremely small and look something like tiny, flexible discs. This unique shape offers many advantages:

• It provides a large surface area to absorb oxygen and carbon dioxide.
• Its flexibility allows it to squeeze through capillaries, the tiny blood vessels that join the arteries and veins.

Abnormally shaped or sized erythrocytes are typically destroyed and eliminated.

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Blood Cell Production (Erythropoiesis)

The actual process of making red blood cells is called erythropoiesis. (In Greek, erythro means "red," and poiesis means "the making of things.") The process of manufacturing, recycling, and regulating the number of red blood cells is complex and involves many parts of the body:

• The body carefully regulates its production of red blood cells so that enough are manufactured to carry oxygen but not so many that the blood becomes thick or sticky (viscous).
• Most of the work of erythropoiesis occurs in the bone marrow. In children younger than 5 years old, the marrow in all the bones of the body is enlisted for producing red blood cells. As a person ages, red blood cells are eventually produced only in the marrow of the spine, ribs, and pelvis.
• If the body needs more oxygen (at high altitudes, for instance), the kidney triggers the release of the hormone erythropoietin (EPO), a hormone that acts in the bone marrow to increase the production of red blood cells.
• The lifespan of a red blood cell is 90 - 120 days. The liver and the spleen remove old red blood cells are removed from the blood by the liver and spleen.
• When old red blood cells are broken down for removal, iron is returned to the bone marrow to make new cells.

Click the icon to see an image of the formed elements of blood.

Click the icon to see an image of hemoglobin.

Review Date: 01/13/2011
Reviewed By: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org).