For example, a dermatopathologist specializes in skin diseases a neuropathologist, in diseases of the nervous system. Although general pathology and systemic pathology are educationally useful divisions of the discipline, pathologists are seldom categorized as general pathologists or systemic pathologists but, instead, are often classified as specialists in a particular organ system. Pathologists are specialists in the discipline of pathology. There is no optimum arrangement of the organ system chapters, so pathology of organ systems can be taught in different sequences in different curricula. It also helps to remember that most organs or tissues respond in a similar way to a particular type of injury, hence the value in mastering the concepts of general pathology before the organ system approach. Again, this subdivision is arbitrary, and the student must bear in mind that disease seldom, if ever, affects only one organ or tissue. As for general pathology, the learning process is simplified by categorization, so Section II of this book is arranged in chapters based on a particular organ system. It is not a separate discipline from general pathology, but a different approach to the study of disease, in which the principles of general pathology are applied at the level of the tissue or organ or even the entire body. Systemic pathology is the study of systemic disease (i.e., disease that affects the system, meaning the entire organism). In subsequent general pathology chapters of Section I, more emphasis will be placed on the interaction among cells of different types, as well as the interaction of cells with their stroma, with other organ systems, and with circulating cells and molecules. This first chapter is focused on the cellular responses to injury, not only on the degeneration that can progress to cell death but also on the adaptations of surviving cells. These reactions not only extend beyond the injured cell to the organ or organismal level but also can occur simultaneously or in rapid succession. However, in the living body, cell injury provokes a variety of vascular, inflammatory, and immune-mediated responses in addition to disturbances of growth.
These categorizations simplify the teaching and learning of general pathology. In the first six chapters of this book, the response to injury is classified as cellular adaptations (degenerative, regenerative, or restorative), vascular disorders, inflammation, or neoplasia, with an additional chapter on the mechanisms of infectious diseases and one on disorders of immunity. General pathology is the study of the reaction of cells or tissues to injury with a focus on the mechanisms of that response.
Although this layout parallels the instruction of pathology in many veterinary schools, the division into general pathology and systemic pathology is somewhat artificial. This pathology textbook begins with a 6-chapter general pathology section followed by 15 chapters of pathology of organ systems (systemic pathology). Pathology is the study of disease from all perspectives. This information will serve as the underpinnings for materials presented in the remaining chapters covering general pathology and for comprehending materials presented on disease mechanisms and pathogeneses in subsequent chapters that cover pathology of organ systems. The goals of this chapter are to explain and illustrate the structure and function of cells and how they are interconnected with mechanisms of and responses to cell and tissue injury, such as adaptation, degeneration, and death.
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