**Question:** Most radiosensitive cell is: March 2009

**Core Concept:** Radiosensitivity refers to a cell's or tissue's response to ionizing radiation, which can cause damage to its DNA and lead to cell death or mutations. The radiosensitivity varies among different cell types and tissues.

**Why the Correct Answer is Right:** The correct answer is **D.** Neurons, specifically sensory neurons, are highly radiosensitive due to their long life span and the fact that they undergo minimal cell division. Radiation exposure can lead to permanent loss of sensory function, as these neurons are crucial for sensory perception and communication between the central and peripheral nervous systems.

**Why Each Wrong Option is Incorrect:**

A. Embryonic cells (Option A) are generally considered radioresistant due to their rapid cell division and DNA repair mechanisms.
B. Mitotic cells (Option B) are generally radioresistant as they have a higher rate of cell division, allowing for repair and regeneration of damaged cells.
C. Neurons (Option C) are not the most radiosensitive among the options provided. While they are indeed radiosensitive, the correct answer (D) refers to sensory neurons, which are more radiosensitive compared to other neurons and cell types.

**Clinical Pearl / High-Yield Fact:**

Understanding radiosensitivity among different cell types is crucial for radiation therapy planning, as it helps to minimize damage to healthy tissues while maximizing the therapeutic effect on cancerous cells. By targeting radiosensitive cells, such as sensory neurons, radiation therapy can be more effective in treating certain cancers while minimizing side effects.