Rank tissues by radiosensitivity from most to least sensitive, selecting the correct sequence.

Rank tissues by radiosensitivity from most to least sensitive, selecting the correct sequence.

• A. Bone marrow > GI tract > CNS
• B. GI tract > Bone marrow > CNS
• C. CNS > GI tract > Bone marrow
• D. Bone marrow > CNS > GI tract

Answer: (A)

Radiosensitivity tracks how quickly cells divide and how specialized they are. Tissues with rapid cell turnover have cells that are actively dividing, making them more vulnerable to radiation-induced DNA damage. Bone marrow is packed with hematopoietic cells that are constantly dividing, so it is highly radiosensitive. The lining of the GI tract also has rapidly renewing crypt and mucosal cells, giving it very high sensitivity as well. The CNS, on the other hand, consists mainly of mature, non-dividing neurons (with relatively few actively dividing cells) and has protective barriers, which makes it much more resistant to radiation. Therefore, the sequence from most to least sensitive is bone marrow, then GI tract, then CNS.