Pathophysiology, Clinical Manifestations, and Etiology of Sickle Cell Disease

Module 1X: Sickle Cell Disease
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Module 1X: Sickle Cell Disease
Initial Discussion:
The patient has Sickle cell disease (SCD), a group of hereditary disorders characterized by the presence of the existence of hemoglobin S (HbS) within the erythrocytes. SCD is transmitted in an autosomal recessive manner, and individuals tend to experience low oxygen levels (hypoxia). The symptom is partly because hemoglobin S has a lower oxygen-carrying capacity. Sickle cell anemia carrier status is associated with protection against malaria, and the prevalence of this disease coincides geographically with the areas with high malaria incidences. The patient's hematocrit is 25%, and this level indicates too few red blood cells, one of the complications in SCD.
Pathophysiology of SCD
Sickle cell disease is an autosomal recessive inheritance defect characterized by Hemoglobin S (HbS) in the erythrocyte where the red blood cells are misshaped, affecting their ability to carry oxygen. HbS is characterized by polymerization with deoxygenation and an abnormal or mutated form of hemoglobin. The altered hemoglobin is not only deoxygenated. It is also crystallized and in a sickle shape rather than disc shape (Hubert & VanMeter, 2018). The cell membrane in individuals with SCD gets damaged, causing hemolysis, and the cells have a lifespan of 20 days instead of the normal 120 days (Hubert & VanMeter, 2018). Increasing oxygen may reverse some of the sickle cells, but over time they are irreversible, leading to hemolysis. Hemoglobin S can transport oxygen in a normal fashion, but there is low erythrocyte leading to low blood hemoglobin levels.  
Clinical manifestations of Sickle cell disease
Vaso-occlusive crisis and hemolytic anemia are two of the main clinical manifestations of SCD that often cause pain and tissue ischemia. Hemolytic anemia is the condition where the blood cells are misshapen and get destroyed at a faster rate than normal. Hemolytic anemia symptoms include fatigue, jaundice, weakness, and irritability (Huether et al., 2020). Sickle-shaped red blood cells or sickle cells are rigid and lose elasticity for smooth blood circulation. 
The vaso-occlusive crisis is a pain crisis that mainly affects the bones of the hands, feet, legs, chest, and spine. However, extensive sickling can also cause three other types of crises: aplastic crisis, sequestration crisis, or hyperhemolytic crisis, and the latter is rare (Huether et al., 2020). The sickle-shaped red blood cells tend to form aggregates that obstruct circulation (vaso-occlusion) and interact with the endothelium, platelets, and leukocytes, leading to ischemia and injuries to various organs.
Etiology
The HbS gene is recessive and common among people from Africa and the Middle East. Among homozygotes, the normal hemoglobin (hemoglobin A [HbA]) is replaced by HbS, resulting in sickle cell anemia symptoms (Hubert & VanMeter, 2018). However, there are vast differences in the severity of the anemia. More than half of the hemoglobin is normal among heterozygotes, and SCD clinical signs occur when there is severe hypoxia and specific instances such as high altitudes and pneumonia. Such cases...