Ionizing radiation possesses enough power to remove electrons from atoms or molecules, a process known as ionization. This energy, from sources like X-rays, gamma rays, and alpha particles, can travel through living tissue. When it interacts with cells, ionization can break chemical bonds, potentially leading to cellular damage. Such damage can alter a cell’s DNA, cause its death, or lead to abnormal reproduction.
How Cell Characteristics Affect Radiation Damage
A cell’s susceptibility to ionizing radiation is influenced by several biological factors. Highly specialized, or differentiated, cells generally exhibit less sensitivity to radiation than less specialized or undifferentiated cells.
The rate at which cells divide, or their proliferation rate, plays a significant role. Rapidly dividing cells are more sensitive to radiation, as their DNA is more exposed and vulnerable during replication. Conversely, cells with slower division rates have more time to repair any damage.
Metabolic activity also contributes to a cell’s response. Cells with elevated metabolic rates tend to be more susceptible. Furthermore, oxygen within a cell affects its sensitivity. Oxygenated cells are generally more sensitive to ionizing radiation, a phenomenon referred to as the oxygen effect. Cells in anoxic conditions can be two to three times more resistant to certain types of radiation compared to well-oxygenated cells.
Cells That Resist Radiation Damage
Certain cell types demonstrate a higher resistance to ionizing radiation. Mature nerve cells, or neurons, are among these, largely due to their high degree of differentiation and their inability to divide.
Mature muscle cells also exhibit low sensitivity to radiation. Like nerve cells, they are highly differentiated and do not undergo frequent division.
Mature red blood cells are another example of cells with low radiosensitivity. These cells are unique because they lack a nucleus and thus do not contain DNA, the primary target for radiation-induced damage. This absence makes them less susceptible. Mature cartilage and bone cells also show relatively low radiosensitivity, primarily because they are fully differentiated and have very low rates of cell division.
Cells Most Vulnerable to Radiation Damage
In contrast to resistant cells, several cell types are highly susceptible to ionizing radiation. Cells found in bone marrow, specifically hematopoietic stem cells, are extremely sensitive due to their continuous and rapid division to produce various blood cells.
Reproductive cells, such as sperm-forming cells (spermatogonia) and oocytes, are also highly sensitive. Cells lining the digestive tract, known as epithelial cells, are highly vulnerable because they undergo constant and rapid renewal.
Hair follicle cells also demonstrate high sensitivity to radiation. Their continuous growth and rapid proliferation make them easily affected, often leading to hair loss after significant radiation exposure.