Pathology

Pathology is the scientific study of disease processes that affect normal anatomy and physiology. Training in pathology requires a medical degree and roughly five years of postgraduate study. Anatomical and physiological changes are pathological changes when they result from an underlying disease process or abnormality.

Since ancient times, physicians have concerned themselves with the distinguishing features of health and disease. Until the early nineteenth century, however, their ideas were based on a theory of humors (that is, elemental fluids in the body), rather than systematic examination of body parts and disease processes. Disease was believed to result from an imbalance of these humors. Dissection of dead bodies to learn about disease was not allowed by religious leaders and obstructed progress in the study of anatomy and pathology through the Middle Ages (350–1450). By the Renaissance (from the fourteenth to sixteenth centuries), however, reports from post-mortem dissections began to provide a new and important source of information contributing to medical knowledge. In his Universa medicina, Jean François Fernel (1497–1558) introduced the term “pathology” to describe the abnormalities detected by anatomists when they dissected cadavers. However, Fernel still held to the ancient teachings of the humors.

In the eighteenth century, the anatomical basis of disease began to emerge. Public hospitals provided a seemingly endless supply of corpses for dissections after death, and hospitals became centers for teaching and practicing morbid anatomy (the abnormal structures in the body associated with disease). By the second half of the eighteenth century, in both the United States and Europe, surgeons and physicians had already begun to correlate signs and symptoms of patients with findings from autopsies after the patients died.

In 1761, Giovanni Battista Morgagni (1682–1771) published the first textbook to systematically detail morbid anatomy and to locate diseases within individual organs. However, humoral theories remained firmly entrenched, and the study of anatomy was still limited to what pathologists could observe of organs, muscles, and bones with the naked eye. All the same, as a result of their investigations into corpses, pathologists in many different countries were beginning to ask questions about what made a tumor benign or malignant, the nature of pus, how wounds heal, and whether blood clots are beneficial or harmful.

Major progress was quick to follow. In France, Marie Francçois Xavier Bichat (1771–1802) studied tissues rather than organs. One of his important contributions was the announcement that the disease of a tissue is the same no matter which organ the tissue is in. Bichat worked without the aid of a microscope. However, the introduction of improved compound microscopes in the 1820s made it possible to study both normal and diseased tissue more extensively and more accurately than ever before. In 1858, Rudolf Carl Virchow (1821–1902) proved conclusively that diseases arose in the cells of organs and tissues, not in the organs and tissues generally. Not long after, the investigations of Louis Pasteur (1822–1895) and Robert Koch (1843–1910) into bacteria were a major step in rounding out understanding of how disease works.

By the end of the nineteenth century, pathology had come into its own as a separate medical specialty. In the twenty-first century, pathologists perform, evaluate, or supervise diagnostic tests, using materials from living or dead patients. Their work is carried out primarily in the laboratory, and they work closely with physicians who are directly in charge of patients. Among the materials a pathologist examines (in procedures generally known as biopsies) are surgically removed body parts, blood and other body fluids, urine, feces, and so on. Pathologists also practice autopsy, which allows them to reconstruct the end of the physical life of a dead person by providing information about the workings of disease they would not be able to get any other way. It is not possible for any one person to know all there is to know about pathology, so pathologists who specialize in one area or another frequently work together. For example, pediatric pathology studies disease processes in children. Forensic pathology is a subspecialty whose goal is to clarify crimes or legal issues.

Advances in laboratory techniques and increasingly fine-scaled instrumentation have greatly expanded the information available to the pathologist in determining the causes of disease. Research in genetics is also changing the study of pathology. More and more, pathologists are being called on to examine the molecular structure of deoxyribonucleic acid (DNA) and to identify molecular markers of disease, as well as to study the impact of environmental factors on heredity.

Pathologists play an increasingly important role in diagnosis, research, and in the development of clinical treatments for disease. A specialized branch of pathology, forensic pathology, offers a vast array of molecular diagnostic techniques (including DNA fingerprint analysis) toward identification of remains, gathering of evidence, and identification of suspects.

Research in pathology often focuses on identifying processes of abnormal cell growth, the causes of general morphologic changes, and the extent or effects of necrosis, infection, inflammation and other processes associated with disease or injury. Pathologists often work with public health professionals to collect data essential to understanding the prevalence and etiology (origin or cause) of specific diseases.

Modern pathology laboratories rely heavily on molecular biology techniques and advances in biotechnology. During the last two decades, there have been tremendous advances in linking changes in cellular or tissue morphology (i.e., gross appearance) with genetic and/or intracellular changes. In many cases, specific molecular tests can definitively identify disease process, and of critical importance to the treatment of disease, and make a correct diagnosis at an earlier stage in the disease process.

Pathologists attempt to relate observable changes to disease process. Whether the changes are evident morphologically—or are distinguishable only via sophisticated molecular tests—the goal is to determine the existence and/or etiology of disease (the cause of disease). Once the etiologic agents are identified, the general goal of research is to document and gather evidence of the pathogenesis of disease (i.e., the mechanisms by which etiologic agents cause disease).

On a daily basis, pathologists perform a broad spectrum of tests on clinical samples to determine anatomical and physiological changes associated with a number of disease processes, including the detection of cancerous cells and tumors.

Major branches of pathology include the study of anatomic, cellular, and molecular pathology. Specific clinical studies often focus on transplantation pathology, neuropathology, immunopathology, virology, parasitology, and a number of clinical subspecialties (e.g., pediatric pathology).

See also Aging and death; Forensic science.