Final answer:
Red blood cells are typically produced in the bone marrow but can be produced in the spleen under extreme conditions such as severe anemia or bone marrow damage. Conditions like sickle cell anemia, thalassemia, and aplastic anemia can lead to extramedullary hematopoiesis in the spleen.
Step-by-step explanation:
In adults, red blood cells (RBCs) are primarily produced in the bone marrow; however, the spleen (and also the liver) can produce RBCs in instances of extreme anemia or when certain diseases, such as bone cancer, damage the bone marrow. This is referred to as extramedullary hematopoiesis. The spleen is not normally the site of significant RBC production in healthy adults. Conditions like sickle cell anemia, thalassemia, and aplastic anemia can all affect RBC production and/or survival, leading to an increased necessity for the spleen to compensate for the decreased RBC counts. Sickle cell anemia causes RBCs to become crescent-shaped and rigid, reducing their ability to carry oxygen and causing them to block small blood vessels, leading to pain and potential organ damage. Similarly, thalassemia involves a genetic defect that affects hemoglobin production, while in aplastic anemia, the bone marrow fails to produce sufficient RBCs due to damaged stem cells.