Sickle Cell Disease Term Paper

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Sickle cell disease or Sickle Cell Anemia (as it used to be called) is a disease of the red blood cells, which in inherited. It was first reported in Western Literature in 1910, when a midwestern physician described a patient from the West Indies who had an anemia, which was characterized, by unusually shaped cells. In the 1920s, it was shown that the change of these cells into the usual sickle shape was associated with conditions of low oxygen. The abnormal hemoglobin associated with sickle cell disease was first demonstrated in 1948, when the process of protein electrophoresis showed that the hemoglobin in patients with sickle cells was different than the average patient.

Pathophysiological Basics of Sickle Cell Disease

Before one can speak in depth on sickle cell disease itself, one must understand the basic pathophysiology which surrounds the condition. Hemoglobin is a protein carried by red cells, which carries oxygen from the lungs for delivery to peripheral tissues. It is composed of two similar proteins, alpha and beta. It is the coordinated action of the alpha and beta globin chains which allow the oxygen transport to occur. These two chains combine to form hemoglobin. During life, except during the very first week of embryonic development, one of the globin chains in an alpha. A developing fetus also has another chain which is a gamma globin; sometimes called non-alpha is present in the fetal circulation. The gamma globin is replaced shortly after birth with the beta, which then chains with the alpha.

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When two alpha chains combine with two gamma chains, this is called Hemoglobin F, or the common hemoglobin of fetal circulation. Adult hemoglobin, formed of two alpha and beta chains is called Hemoglobin a. If one alpha and one non-alpha chain combine, then this two chain combination is called a dimer and it not functional enough to deliver oxygen to tissues.

Term Paper on Sickle Cell Disease Assignment

Sickle cell disease is most commonly seen in patients from Africa, India, the Mediterranean and the Middle East. A genetic mutation caused there to be a change in one of the amino acids which build hemoglobin. While the alpha globin is normal, in sickle cell disease the beta unit has a substitution of valine for glutamic acid at position six on the amino acid chain. All the other amino acids in sickle and normal hemoglobin are the same.

The basis of this mutation is genetic in character. Since DNA determines the way amino acids are paired, it is a mutation within the DNA, specifically on chromosome 11, which is the gene that controls the production of the beta subunit, which causes the presence or absence of sickle cell disease. Because of the association with the chromosomes, sickle cell anemia is an inherited disease.

There are different expressions of this disease. If only one of the beta globins has a "sickle" gene and the other one is normal, then that person is considered a carrier for sickle cell disease. These people will not actually manifest the disease, but may pass it on to their offspring. This type of expression is called sickle cell trait. If both beta globin genes are affected, and have the substitution, then this patient has sickle cell disease. Inheritance is the only way of acquiring sickle cell disease.

Several factors are associated with the expression and variability of sickle cell disease. The presence of hemoglobin C. On it's own generally causes no problems, a person who has two genes for the expression of hemoglobin C. can also have a relatively harmless disease called Hemoglobin C. disease. If the patient has C. And hemoglobin S, this is called Hemoglobin SC disease. This can cause a disease as severe as sickle disease. This condition may also coexist with sickle cell disease and cause a problem with red cell dehydration.

As we have stated the hemoglobin picks up oxygen in the lungs and releases it in the periphery. Normal hemoglobin molecules exist as single units within normal, red, disc shaped cells. Sickle hemoglobin also live as isolated units within the red cells when they are exposed to sufficient oxygen. but, in contrast to normal hemoglobin, when sickle hemoglobin delivers the oxygen to the tissues, the hemoglobin molecules have a tendency to stick together and form into long chains.

These chains cause the cell to bend in a crescent shape, or "sickle" shape, hence why the disorder is called sickle cell disease. When the cells are once again oxygenated, then the cell will resume its normal shape. As you can imagine, this causes the red cell to change shape many times over and over again. These changes cause physical damage to the red cell and the hemoglobin. Ultimately, the sickled hemoglobin gets to the point where it cannot revert to the single strands, but instead gets twisted into long braided bundles. The bundles get attacked to even larger and longer bundles which can stretch and change the shape of the cell. I found an interesting analogy on a sickle cell disease website which described the next process in this manner -"the bundles self associate into even larger structures which stretch and distort the cell. The analogy would be a water balloon that was stretched and deformed by icicles. The stretching of the balloon's rubber is similar to what happens to the membrane of the red cell. Polymers tend to grow from a single start site, called a nucleation site, and often grow in multiple directions. Start shaped clusters of hemoglobin S. develop commonly."

The hemoglobin S. that appears in the sickling situation is only maintained as a polymer group by the weakest of forces. The association of valine with the beta chain makes the bands between the twisted hemoglobin structures very weak. Unfortunately, the polymerization that occurs in the sickling cells not only changes the shape of the cells but also makes the walls of the cells rigid. Sometimes the cells can become wedged in the smaller blood vessels, which can then cause micro-infarction to the local tissue. The end result is pain and often organ damage due to hypoxia. This damage to the red cells can also be the cause of the many complications of sickle cell disease. Free heme can be released from the cell during the repeated actions of polymerization/depolymerization and results in the formation of reactive oxygen compounds. Antibodies can develop to these compounds, which attack the red cells themselves and result in even more hemolysis and a greater degree of anemia than is already seen as a result of the red cell destruction.

The bone marrow tries to keep up production to replace the red cells destroyed in sickle cell disease, but in most patients it is generally not fast enough. As a result, the amount of bone marrow, which actively produces cells in the sickle cell patient, is much greater than in patients with normal hemoglobin.

How anemic the patient is will differ from patient to patient. A typical patient with sickle cell disease will have a hematocrit around 25%, whereas the normal hemoglobin patient will run around 45%. The method of expression of the disease can also affect the degree of anemia. For example, a patient who has hemoglobin SC disease (Where one beta globin is coded for S. And the other beta globin is coded for C) have higher hematocrits than patients who have both beta globins coded for S (Hemoglobin SS disease). Patients who have sickle cell trait have normal blood counts.

People with a family history of sickle cell disease are understandably concerned that they may have the disease themselves, and want testing. Routine blood cell counts (CBCs) cannot identify sickle cell disease. The best test for diagnosis is the hemoglobin electrophoresis that can detect the different hemoglobins and can also answer as to whether the patient has Hemoglobin C. Or thalassemia as well.

Most newborns in the United States are tested at birth for all these diseases.

Physical Manifestations of Sickle Cell Disease

The most common presentation of sickle cell disease in the adult is what is called a vasoocculsive crisis. This usually begins in response to some change in the body, such as a fever, being at a high altitude or even just from the temperature change on a hot day. There are times when it is not possible to identify what causes the crisis.

The most common presenting symptom is severe deep pain present in the extremities, usually in the long bones. Another common area of pain is the abdomen. The patient's pain is usually very severe and may be accompanied by fever, malaise, and leukocytosis. This syndrome may last anywhere from a few hours to a few days and it will often begin quickly, and end just as quickly. Anemia is universally present, and in the patient who has not previously been diagnosed, this may be a diagnostic clue. As previously reported, the anemia is chronic and hemolytic. Megaloblastic changes may be seen due to the rapid cellular turnover as well as folate deficiency.… [END OF PREVIEW] . . . READ MORE

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