Introduction to Health Physics: Fourth Edition - Ruang Baca FMIPA UB

BIOLOGICAL BASIS FOR R ADIATION SAFETY 307
ear. The sound pressure on the eardrum activates a mechanical linkage of three tiny
bones (hammer, anvil, and stirrup) collectively called the ossicles. The function of
the middle ear is to mechanically amplify the sound-pressure-induced vibrations of
the eardrum and to transmit these vibrations to the oval window, which is the beginning
of the inner ear. The inner ear is filled with a fluid called the perilymph.
Immersed in the perilymph are two separate systems of ducts that are filled with
another physiological fluid called endolymph. One of these systems, the semicircular
canals, is concerned with regulation of balance. The other one is the cochlea, a spiralshaped
structure in which the mechanical motions of the sound wave are converted
into electrical impulses that are sent to the brain. The oval window is joined to the
stirrup and vibrates due to the forces transmitted via the ossicles. This causes
the endolymph to move back and forth. Immersed in the endolymph is a membrane
(called the organ of Corti) from which numerous hairs project into the endolymph
along the entire length of the membrane. These hairs are parts of the auditory nerve.
The oscillatory motion of the endolymph causes the hairs to bend back and forth,
and this bending generates the electrical impulses that are sent to the brain and are
recognized as sound. The organ of Corti responds to the frequency and pressure
level of the sound waves.
Radiation at levels of interest in the practice of health physics does not lead to
any decrement in hearing acuity. However, loud noise, in excess of 90 dB, does lead
to hearing loss. Noise control therefore is important in areas where loud noises may
be generated, such as the turbine floor in a nuclear power plant.
Unity of the Body
The description of the physiological basis for radiation dosimetry sounds as if the
various organ systems were independent entities. Nothing, however, could be further
from the truth. The body can be thought of as a system of integrated negative
feedback loops that operate together to keep its internal milieu constant. The total
activity of these integrated systems is called homeostasis. In this manner, all the systems
function together in a highly coordinated manner to produce a unified individual.
RADIATION EFFECTS: DETERMINISTIC
Acute Effects
Acute whole-body radiation overexposure affects all the organs and systems of the
body. However, since not all organs and organ systems are equally sensitive to radiation,
the pattern of response, or disease syndrome, in an overexposed individual
depends on the magnitude of the dose. To simplify classification, the acute radiation
syndrome is subdivided into three classes. In order of increasing severity, these are
(1) the hemopoietic syndrome, (2) the GI syndrome, and (3) the CNS syndrome
(Table 7-4). Certain effects are common to all categories; these include the following:
nausea and vomiting
malaise and fatigue
increased temperature
blood changes
In addition to these effects, numerous other changes are seen.