Pathology: The Clinical Description of Human Disease

This chapter discusses the fundamental concepts, terminology, and practice of pathology as the discipline dedicated to the understanding of causes, mechanisms, and effects of diseases. It describes some key terms, definitions, and concepts, presents historical human approaches to diseases, and provides an overview of current diagnostic practice and a vision for new interface with applied molecular biology. Pathology refers to the specialty of medical science concerned with the cause, development, structural/functional changes, and natural history associated with diseases. Disease refers to a definable deviation from a normal phenotype (observable characteristics due to genome and environment), evident via patient complaints (symptoms), and/or the measurements of a careful observer (signs). The cause of the disease is referred to as its etiology. One disease entity can have more than one etiology, and one etiology can lead to more than one disease. Each disease entity develops through a series of mechanistic chemical and cellular steps. This stepwise process of disease development is referred to as its pathogenesis. Pathogenesis can refer to the changes in the structure or function of an organism at the gross/clinical level and the stepwise molecular abnormalities leading to changes in cellular and tissue function. The presentation of a disease to a clinician is in the form of a human patient with variably specific complaints (symptoms), to which the examining physicians can add diagnostic sensitivity and specificity by making observations (screening for signs of diseases).