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Sickle cell disease

Description

An in-depth report on the causes, diagnosis, and treatment of sickle cell disease.


Alternative Names

Sickle cell anemia


Introduction

Hemoglobin is a complex molecule and the most important component of red blood cells. Sickle cell disease occurs from genetic abnormalities in hemoglobin. Three forms of hemoglobin are important in this disorder:

Hemoglobin
Hemoglobin is the most important component of red blood cells. It is composed of a protein called heme, which binds oxygen. In the lungs, oxygen is exchanged for carbon dioxide. Abnormalities of an individual's hemoglobin value can indicate defects in red blood cell balance. Both low and high values can indicate disease states.

Changes that Lead to Sickle Cell Disease

Sickle cell disease is a result of changes in hemoglobin S:

The severity of sickle cell disease generally depends on a number of factors:

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 5.2 million red blood cels per cubic millimeter of blood, and women have about 4.7 million red blood cells per cubic millimeter of blood. To understand red blood cells and their role in anemia, it is useful to know certain facts about them.

Hemoglobin and Iron

Each red blood cell contains 200 - 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 present in hemoglobin can be recycled and reused.

Structure and Shape

Red blood cells 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 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 90 - 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.

Oxygen Loss in Red Blood Cells with Normal Hemoglobin

In everyone, hemoglobin loses its oxygen normally in a number of ways:

  • To sustain life, oxygen regularly passes from red blood cells to the tissues where it is needed to perform vital functions.
  • Hemoglobin loses oxygen if blood cells become too acidic, for example, after strenuous exercise.
  • Going to high altitudes or any stressful activity or situation that increases the body's demand for oxygen depletes its supply in red blood cells.

Such situations do not affect normal red blood cells that contain hemoglobin A.


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