Final answer:
The myelophthisic process is the pathologic condition that replaces bone marrow and impairs hematopoiesis, causing pancytopenia.
Step-by-step explanation:
The pathologic process that replaces bone marrow and impairs hematopoiesis, resulting in pancytopenia, is known as the myelophthisic process. This process occurs when myeloid stem cells within the bone marrow are either defective or are replaced by other cells, such as cancer cells, leading to insufficient production of red blood cells (RBCs), white blood cells (WBCs), and platelets. The myelophthisic process can cause clinical manifestations like an enlarged spleen due to extramedullary hematopoiesis, where the spleen and liver attempt to compensate for the impaired function of the bone marrow.
Myelofibrosis is an example of a disorder characterized by bone marrow fibrosis and inflammation, which similarly hinders hematopoiesis. Factors such as radiation, medication, chemotherapy, infection, and certain inherited conditions like aplastic anemia and thalassemia can also lead to the destruction of red marrow, further impairing the production of formed elements such as erythrocytes, leukocytes, and platelets.