Anemia - Introduction

Introduction

Anemia is an abnormal reduction in red blood cells.

This phomicrograph shows normal red blood cells (RBCs) as seen in the microscope after staining.

Anemia�is a great problem globally, and worse in developing countries, but it is by no means absent in industrialized nations. An estimated 3.4 million Americans suffer from anemia. Anemia is not a single disease but a condition, like fever, with many possible causes and many forms. Causes of anemia include nutritional deficiencies, inherited genetic defects, medication-related side effects, and chronic disease. It can also occur because of blood loss from injury or internal bleeding, the destruction of red blood cells, or insufficient red blood cell production. The condition may be temporary or long term, and can manifest in mild or severe forms.

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As it is impossible to discuss all types of anemia, this report focuses on three of the most common forms:

Iron deficiency anemia
Anemia of chronic disease (ACD)
Megaloblastic anemia (caused by deficiencies in the B vitamins folate, vitamin B12, or both)

Some less common causes and types of anemia are included in a table in this report.

Blood

Blood has two major components:

Plasma is a clear yellow liquid that contains proteins, nutrients, hormones, electrolytes, and other substances. It constitutes about 55% of blood.
White and red blood cells and platelets make up the balance of blood. The white cells are the infection fighters for the body, and platelets are necessary for blood clotting. The important factors in anemia, however, are red blood cells.

Red blood cells (RBCs), also known as erythrocytes, carry oxygen throughout the body to nourish tissues and sustain life. Red blood cells are the most abundant cells in our bodies; men have about 5,200,000 and women about 4,700,000 per cubic millimeter of blood.

Hemoglobin and Iron

Each red blood cell contains between 200 and 300 hemoglobin molecules. Hemoglobin is a complex molecule and the most important component of red blood cells. It is composed of protein (globulin) and a molecule (heme), which binds to iron.

In the lungs, the heme component binds to oxygen in exchange for carbon dioxide. The oxygenated red blood cells are then transported to the body's tissues, where the hemoglobin releases the oxygen in exchange for carbon dioxide, and the cycle repeats. The oxygen is used in the mitochondria, the power source within all cells.

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 inner tubes. 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.

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 requires an increase in 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 life span of a red blood cell is between 90 and 120 days. Old red blood cells are removed from the blood by the liver and spleen.
There they are broken down and 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.

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