Physiologists conduct a study to evaluate erythropoiesis in various age groups. In one of the studies, healthy individuals who experience acute traumatic blood loss are enrolled. They divide the patients in 2 groups: younger individuals with a mean age of 35 years and older adults with a mean age of 70. These patients have normal iron, folic acid, vitamin B₁₂, and plasma protein studies. Results indicate that older patients with acute traumatic blood loss have a much lower reticulocyte count and a much longer time to recovery to pretrauma hemoglobin level when compared to younger patients. Which of the following age-related processes best explains the observed findings?

Question

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Although patients with advanced age typically have normal serum blood counts, age-related changes in cytokine signaling and the cellular composition of the bone marrow impairs the generation of new cells in response to acute stressors such as blood loss or hypoxia. When compared to younger patients, the bone marrow of older patients has a higher quantity of fat and a reduced overall mass, which limits the functional reserve of hematopoietic cells. In addition, hematopoietic progenitor cell diversity and the response to stimulatory cytokines (eg, stem-cell factor, granulocyte macrophage colony-stimulating factor) are also impaired, thereby limiting the generation of new cells in response to stress. Because of these changes, older individuals cannot rapidly generate new blood cells. (Choice B) Patients with advanced age generally have increased (not decreased) medullary cavity size due to loss of endosteal cortical bone. This increases the risk of fractures. (Choice C) Red blood cell life span is preserved in patients with advanced age; therefore, healthy older individuals usually have normal hemoglobin level. However, they are much less capable of generating new erythrocytes in times of blood loss or other stressors (eg, hemolysis). (Choice D) Extramedullary hematopoiesis is common in newborns but does not generally occur in older patients unless there is insufficient marrow space for hematopoietic cell proliferation. Therefore, extramedullary hematopoiesis is typically associated with significant bone marrow pathology (eg, myelofibrosis). (Choice E) Although bone marrow fat increases with age, bone marrow fibrosis is not a part of normal aging. Bone marrow fibrosis is associated with primary myelofibrosis, a chronic myeloproliferative disorder marked by anemia and extramedullary hematopoiesis (hepatosplenomegaly). Educational objective: Patients of advanced age have increased bone marrow fat and reduced bone marrow mass, leading to impaired bone marrow reserve. This results in an inability to rapidly generate new blood cells in response to acute stress (eg, blood loss, hypoxia).

Physiologists Conduct a Study to Evaluate Erythropoiesis in Various Age