Anemia

I   INTRODUCTION

Anemia,   medical condition caused by an abnormally low number of red blood cells. Red blood cells, also called erythrocytes, contain hemoglobin, a red, iron-rich protein that carries oxygen in the blood to the body’s tissues. People with anemia develop symptoms caused by the poor delivery of oxygen to their body tissues. These symptoms include pale skin, shortness of breath, rapid heartbeat, low vitality, dizziness, and, if left untreated, stroke or heart failure.

II   CAUSES

There are three primary causes of anemia: (1) reduced production of red blood cells; (2) excessive destruction of red blood cells; and (3) extensive bleeding.

A   Reduced Production of Red Blood Cells

Red blood cell production becomes impaired if the body has inadequate amounts of certain nutrients, including iron, vitamin B12, and folic acid, as well as the hormone erythropoietin, which is produced by the kidneys. Chronic illnesses, such as cancer, kidney disease, diabetes mellitus, and inflammatory bowel disease, may also lead to decreased red blood cell production.

B   Destruction of Red Blood Cells

Red blood cells normally live for about 120 days before the immune system removes them from the body. The body compensates by producing new red blood cells. But if the destruction of red blood cells exceeds the body’s ability to produce new red blood cells, anemia results.

Abnormal destruction of red blood cells may be caused by an enlarged spleen, an organ that removes worn red blood cells from the body. The larger the spleen grows, the more red blood cells it traps and destroys. In some cases red blood cells are destroyed by a malfunction of the immune system in which antibodies attach to red blood cells, marking them for destruction. Red blood cells may also be destroyed by some genetic conditions, such as thalassemia, that cause defects in the structure or function of red blood cells.

C   Bleeding

Excessive bleeding can cause dangerously low...