Which ordering from greatest to least radiosensitivity is correct?

• A. Gastrointestinal system, cerebrovascular system, hematopoietic system
• B. Cerebrovascular system, Gastrointestinal system, Hematopoietic system
• C. Hematopoietic system, Cerebrovascular system, Gastrointestinal system
• D. Hematopoietic system, Gastrointestinal system, Cerebrovascular system

Answer: (D)

Radiosensitivity tracks how actively cells divide and how undifferentiated they are. Tissues with rapid cell turnover and many precursor cells are most vulnerable, while those made up mainly of mature, non-dividing cells are more resistant.

The hematopoietic system has lots of rapidly dividing progenitor cells, so it is the most radiosensitive. The gastrointestinal tract renews its lining quickly as well, giving it high sensitivity, though typically not as high as hematopoietic tissue. The cerebrovascular system mainly contains mature neurons with low turnover, making it comparatively resistant to radiation.

So, from greatest to least radiosensitivity: hematopoietic system, gastrointestinal system, cerebrovascular system.