Explanation
(A) Aplastic anemia is characterized by a lack of reticulocytes in the blood. Platelet and white blood cell counts are usually not depressed. It is usually self-limiting, lasting 5-10 days. (B) Vaso-occlusive crisis is the most common type of crisis in sickle cell anemia. Sickled cells become clogged, leading to distal tissue hypoxia and infarction. Joints and extremities are the most commonly affected areas. (C) Dactylitis crisis, or
"hand-foot syndrome," causes symmetrical infarction of the bones in the hands and feet, resulting in painful swelling in the soft tissues of the hands and feet. (D) Sequestration crisis occurs as enormous volumes of blood pool within the spleen. The spleen enlarges, causing tenderness. Signs of shock including pallor, tachypnea, and faintness result, related to the deficient intravascular volume. This type of crisis is potentially fatal.