Pathology (from Greek pathos, feeling, pain, suffering; and logos, study of; see also -ology) is the study of the processes underlying disease and other forms of illness, harmful abnormality, or dysfunction. Within biology but also a branch of medicine, it means specifically the study and diagnosis of the structural and functional changes in cells, tissues and organs that underlie disease. Another name for pathology is laboratory medicine.

Scope of pathology

The primary goal of pathology is the study of the four main aspects of a disease:

• Etiology: what causes the disease
• Pathogenesis: the mechanism by which a certain etiological factor causes disease
• Morphologic changes: the structural changes induced in the cells, tissues and organs
• Clinical significance: the functional consequences of the morphologic changes

Tools of pathology

The techniques used most often in the study of the disease process and hence diagnosis are:

• Gross pathology: the recognition of disease based on naked-eye examination of surgical specimens or at autopsy.
• Histology: the microscopic study of tissues. Histopathology is the science of diagnosing diseases on the basis of the histological aspect of the diseased tissues.
• Cytology: the study of detached cells. Cytopathology is the science of diagnosing diseases on the basis of the cytological aspects of detached cells. The most common application of this technique is the Pap smear.
• Clinical Chemistry
• Immunology
• Flow cytometry
• Molecular Biology techniques, like PCR and FISH are increasingly useful to diagnose diseases.

Branches of pathology

Medicine

To practice pathology in the U.S., the American Board of Pathology requires medical training (usually four years) followed by three to four years of post-graduate training in Pathology. Finally, a board certification examination is required. Other countries have very similar requirements.

The American Board of Pathology recognizes the following sub-specialties within Pathology:

Primary certifications

• Anatomic Pathology, the science of diagnosing diseases based on the appearance, both gross and microscopic appearance of tissues.
• Clinical Pathology, the science of diagnosing diseases based on the analysis of body fluids like blood, urine, etc.

Many candidates seek the combined certification in Anatomic and Clinical Pathology, also called General Pathology.

Dentistry

The American Board of Oral and maxillofacial pathology certifies dentistry doctors, not medical doctors, to practice this sub-specialty of Pathology.

Other

• Plant pathology
• Veterinary Pathology
• Parasitology

• Speech pathology is a quite separate area mostly involved in helping patients with stroke or speech impediments.
• Psychopathology is also used in mental health, denoting the study of mental illness.

Related sciences

• Anatomy, either gross or microscopic (histology)
• Nosology: the science of classifying, or naming, diseases
• Epidemiology: the science of associating diseases with risk factors, regardless of known pathological relationships. An epidemiological association is often the first step in establishing an etiological (causal) relationship between a risk factor and a disease.

Other uses of "pathology"

Pathological is used to describe a person's actions in such a way as to credit the action to a disease process, e.g. pathological purchasing or pathological consumption, pathological narcissism, pathological liar, pathological gambling, pathological jealousy. Pathological is also used casually, to signify an abnormal state, e.g. a "pathological attitude" or a "pathological woman hater".

Pathological is also used in mathematics, physics, and statistics to describe an exceptionally (or awkwardly, or inconveniently) atypical example or set of data, often one which does not abide by rules or succumb to treatment that other similar cases usually do:

• Pathological (mathematics)
• Pathological science

Computer science uses this term in a slightly different sense with regard to the study of algorithms. Here, an input (or set of inputs) is said to be pathological if it causes atypical behavior from the algorithm, such as a violation of its average case complexity, or even its correctness. For example, hash tables generally have pathological inputs: sets of keys that collide on hash values. The term is often used pejoratively, as a way of dismissing such inputs as being specially designed to break a routine that is otherwise sound in practice.