Stress at the Cellular Level
Pathologic processes may
occur at all levels of the biologic or-ganism. If the cell is considered the
smallest unit or subsystem (tissues being aggregates of cells, organs
aggregates of tissues, and so forth), the processes of health and disease or
adaptation and maladaptation can all occur at the cellular level. Indeed,
patho-logic processes are often described by scientists at the subcellular or
molecular level.
The cell exists on a
continuum of function and structure, ranging from the normal cell, to the
adapted cell, to the injured or diseased cell, to the dead cell (Fig. 6-3).
Changes from one state to another may occur rapidly and may not be readily de
The earliest changes occur at the molecular
or subcel-lular level and are not perceptible until steady-state functions or
structures are altered. With cell injury, some changes may be re-versible; in
other instances, the injuries are lethal. For example, tanning of the skin is
an adaptive, morphologic response to expo-sure to the rays of the sun. If the
exposure is continued, however, sunburn and injury occur, and some cells may
die, as evidenced by desquamation (“peeling”).
Different cells and
tissues respond to stimuli with different patterns and rates of response; some
cells are more vulnerable to one type of stimulus or stressor than others. The
cell involved, its ability to adapt, and its physiologic state are determinants
of the response. For example, cardiac muscle cells respond to hy-poxia (inadequate oxygenation) more
quickly than smooth mus-cle cells do.
Other determinants of
cellular response are the type or nature of the stimulus, its duration, and its
severity. For example, neu-rons that control respiration can develop a tolerance
to regular, small amounts of a barbiturate, but one large dose may result in
respiratory depression and death.
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