Figure 4-10. Relative shielding effectiveness of various thicknesses of concrete.
Section V. RADIATION--CELLULAR CONCEPTS
The careless use of x-radiation can incapacitate, disfigure, or even produce
death. Since the x-ray specialist plays such a vital role in reducing radiation exposure
to himself as well as to his patients, it is necessary for him to be knowledgeable of the
concepts involved. This section describes cell structure and activity, how radiation can
affect the cell, and the variation in radiosensitivity of different cells.
4-20. LIFE CYCLE OF A CELL
Reproduction, maturation, and death are the three phases in the life cycle of a
cell. Reproduction is the process in which a cell divides into two cells. In this process,
the genetic operating instructions of the original cell are given to the daughter cells.
Certain highly specialized cells do not reproduce themselves and cannot be replaced if
destroyed. These include nerve cells and, to a large extent, adult muscle tissue. The
blood cells released into the blood stream do not divide, but simply mature and die.
However, those retained in the bone marrow reproduce continually and continue to
liberate blood cells for use in the body. Cellular reproduction and maturation provide
constant tissue repair and growth for the body. If radiation alters cellular processes, the
cell may not reproduce or function correctly.
4-21. CLASSIFICATION OF CELLS
Cells are classified as somatic or gonadal. Differentiation between these
varieties is essential to any discussion of radiation biology, since irradiation produces
distinct effects dependent upon the type of cell involved.