Most radiosensitive tissue of body among the following is –
**Core Concept**
The question is testing the relative sensitivity of different tissues to ionizing radiation, which is a critical concept in radiation oncology and radiobiology. The radiosensitivity of a tissue refers to its susceptibility to damage from radiation, with more sensitive tissues being more prone to injury or death upon exposure.
**Why the Correct Answer is Right**
Bone marrow is considered the most radiosensitive tissue in the body due to its rapid cell division rate and the presence of highly proliferative stem cells. These cells are essential for hematopoiesis, and their destruction can lead to severe bone marrow suppression, resulting in anemia, leukopenia, and thrombocytopenia. The high radiosensitivity of bone marrow is due to the lack of DNA repair mechanisms in rapidly dividing cells, making them more vulnerable to radiation-induced damage.
**Why Each Wrong Option is Incorrect**
**Option A:** The central nervous system (CNS) is relatively resistant to radiation due to its low rate of cell division and the presence of protective mechanisms such as the blood-brain barrier and the ability of neurons to withstand radiation-induced damage.
**Option B:** The gastrointestinal tract is moderately radiosensitive, with the crypt cells of the small intestine being more susceptible to radiation damage than other tissues. However, it is not as sensitive as bone marrow.
**Option C:** The skin is relatively resistant to radiation, with the basal cells of the epidermis being the most radiosensitive component. However, the skin is not as sensitive as bone marrow.
**Clinical Pearl / High-Yield Fact**
The "late effects" of radiation, such as fibrosis and atrophy, are more common in tissues that are relatively resistant to radiation, whereas "early effects" such as bone marrow suppression are more common in highly radiosensitive tissues.
**Correct Answer:** D. Bone marrow.