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INTRODUCTION TO PATHOLOGY
Literally translated, pathology is the study (logos) of disease (pathos, suffering). It involves the investigation of the causes of disease and the associated changes at the levels of cells, tissues, and organs, which in turn give rise to the presenting signs and symptoms of the patient. There are two important terms that students will encounter throughout their study of pathology and medicine:
• Etiology is the origin of a disease, including the underlying causes and modifying factors. It is now clear that most common diseases, such as hypertension, diabetes, and cancer, are caused by a combination of inherited genetic susceptibility and various environmental triggers. Understanding the genetic and environmental factors underlying diseases is a major theme of modern medicine.
• Pathogenesis refers to the steps in the development of disease. It describes how etiologic factors trigger cellular and molecular changes that give rise to the specific functional and structural abnormalities that characterize the disease. Whereas etiology refers to why a disease arises, pathogenesis describes how a disease develops. Defining the etiology and pathogenesis of disease not only is essential for understanding a disease but is also the basis for developing rational treatments. Thus, by explaining the causes and development of disease pathology provides the scientific foundation for the practice of medicine.
To render diagnoses and guide therapy in clinical practice, pathologists identify changes in the gross or microscopic appearance (morphology) of cells and tissues, and biochemical alterations in body fluids (such as blood and urine). Pathologists also use a variety of morphologic, molecular, microbiologic, and immunologic techniques to define the biochemical, structural, and functional changes that occur in cells, tissues, and organs in response to injury. Traditionally, the discipline is divided into general pathology and systemic pathology; the former focuses on the cellular and tissue alterations caused by pathologic stimuli in most tissues, while the latter examines the reactions and abnormalities of different specialized organs. In this book we first cover the broad principles of general pathology and then progress to specific disease processes in individual organs.