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Introduction to Clinical Applications

Objectives
In this chapter we will study • various approaches to the study of disease; • the role of the Centers for Disease Control and Prevention; • common causes of disease; • the distinction between signs and symptoms of disease; • terms used to describe the time course of a disease; and • common abbreviations for medical specialists and specialties.

Homeostasis and Disease
The body’s tendency to maintain internal stability is called homeostasis. Examples include the body’s relatively stable temperature, blood glucose concentration, hormone levels, acid-base balance, and electrolyte balance. When physiological variables deviate too much from their set point, the body activates negative feedback loops that tend to restore stability and maintain health. In some cases, such as the stoppage of bleeding, positive feedback loops are activated to bring about rapid change. If the attempt to regain homeostasis fails, disease results. There is a strong emphasis in medicine today on promoting wellness through prevention. However, this manual focuses on what happens when prevention fails, homeostasis is disrupted, and disease occurs.

The Study of Disease
Disease (illness) is any deviation from normal that interferes with correct, life-sustaining bodily function. Literally, the word means dis-ease, the opposite of ease (comfort and normal function). Disease may have underlying structural foundations, such as a broken bone, and its effects may be observed not just at the level of bodily form and function but also at the level of the mind, as in psychiatric diseases (mental illness). The study of disease is called pathology, a field that embraces all aspects of disease, from the patient’s complaints to the gross and microscopic appearance of dysfunctional tissues and organs. Pathologists are physicians and others who