Which of the following is most sensitive to radiation

Ans: a (Stem cells) Ref: Robbins, 7th ed, p. 437, rsi.muhealth.orgSince DNA is the most important sub cellular target of ionizing radiation, rapidly dividing cells are more radiosensitive than quiescent cellsLaw of Bergonie' and TribondeauRadiation has a more rapid (is more effective) effective against cells that are actively dividing, are undifferentiated and have a large dividing future.Modification by Ancel and VitembergerThe appearance of radiation damage is dependent on two factors:1. The biologic stress on the cell2. The conditions to which the cell is exposed pre and post irradiationThe most important biologic stress is division. So the rapidly dividing cells express damage earlier and slowly dividing cells express damage later.Radiation injury susceptible cells areRadiation resistant tissuesHaematopoeitic cellsBoneGerm cellsCartilageGastrointestinal epitheliumMuscleSquamous epitheliumPeripheral nervesEndothelial cells Lymphocytes