Overview of Cellular Pathophysiology 1.1 Homeostasis The normal cell is capable of making responses to physiologic demands and maintaining a steady state of function referred to as homeostasis. When a new steady state is achieved in response to altered physiologic stress, the process is referred to as adaptation. Adaptations are reversible changes that allow cells to survive Stress, increased demand Nor mo.l Cell ( horneostilSis) /.””‘ bility P'[ ——-.1 to adapt l _ Adaptation ~ ; Injurious stimulus Cell I nj ury) Cell Death A Figure 1- 1.1 Cellular Response to Stress and Injury and function. If the ability of cells to adapt is exceeded, cell injury results, and this is also reversible t o a point.
If the injurious stimulus persists, and adaptation is no longer possible, irreversible cell injury and cell death ensue. 1.2 Causes of Cell Injury Physiologic adaptation to stress can progress to significant cell injury if the stimulus is not removed. A variety of causes of injury exist, including: • Hypoxia: A deficiency of oxygen that reduces aerobic oxidative respiration • Chemical agents/drugs • Infectious agents • Immunologic reactions • Congenital/genetic derangements • Mechanical trauma • Nutritional deficiency or excess 1.3 Variables in Cell Injury The response of cells to injurious stimuli depends on a number of variables: • The nature of the injurious stimulus • The duration of action or injury • The adaptability of specific cells to injury; for example, anoxia causes cell death in: • Neurons: 3 to 5 minutes • Myocardium: 1 t o 2 hours • Fibroblasts: hours