Irradiation of the bone marrow will result in which effect?

• A. Cataracts
• B. Melanoma
• C. Hematological depression
• D. Neurological depression

Answer: (C)

Bone marrow is where blood cells are produced, and its cells are among the most radiosensitive because they divide rapidly. When the marrow is irradiated, these progenitor cells are damaged and cannot keep up with blood-cell production. The result is hematological depression: a drop in red cells (anemia), white cells (immunosuppression and infection risk), and platelets (bleeding risk). This is the direct, primary effect of irradiating bone marrow.

Cataracts come from lens exposure, which is a different tissue; melanoma is a cancer risk associated with radiation exposure in various tissues, not a direct immediate marrow effect; and neurological depression would require significant exposure to the brain.