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A pathologist examines a tissue section for evidence of cancerous cells while a surgeon observes.
| |
| Focus | Disease |
|---|---|
| Subdivisions | Anatomical pathology, clinical pathology, dermatopathology, forensic pathology, hematopathology, histopathology, molecular pathology, surgical pathology |
| Significant diseases | All infectious and organic diseases and physiological disorders. |
| Significant tests | All medical diagnostic tests, particular biopsy, blood analysis, dissection, and other applications of medical microscopy |
| Specialist | Pathologist |
| Glossary | Glossary of medicine |
Pathology (from the Ancient Greek roots of pathos (πάθος), meaning "experience" or "suffering" and -logia (-λογία), "study of") is concerned mainly with the causal study of disease.
The word pathology itself may be broadly refer to the study of disease in general, incorporating a wide range of bioscience research fields and medical practices. However, when used in the context of modern medical treatment, the term is often used in a more narrow fashion to refer to processes and tests which fall within the contemporary medical field of "general pathology," an area which includes a number of distinct but inter-related medical specialties that diagnose disease, mostly through analysis of tissue, cell, and body fluid samples. Idiomatically, "a pathology" may also refer to the predicted or actual progression of particular diseases (as in the statement "the many different forms of cancer have diverse pathologies"), and the affix path is sometimes used to indicate a state of disease in cases of both physical ailment (as in cardiomyopathy) and psychological conditions (such as psychopathy). A physician practicing pathology is called a pathologist.
As a field of general inquiry and research, pathology addresses four components of disease: cause, mechanisms of development (pathogenesis), structural alterations of cells (morphologic changes), and the consequences of changes (clinical manifestations). In common medical practice, general pathology is mostly concerned with analyzing known clinical abnormalities that are markers or precursors for both infectious and non-infectious disease and is conducted by experts in one of two major specialties, anatomical pathology and clinical pathology. Further divisions in specialty exist on the basis of the involved sample types (comparing, for example, cytopathology, hematopathology, and histopathology), organs (as in renal pathology), and physiological systems (oral pathology), as well as on the basis of the focus of the examination (as with forensic pathology).
Pathology is a significant field in modern medical diagnosis and medical research.
General medical pathology
The
modern practice of pathology is divided into a number of subdisciplines
within the discrete but deeply interconnected aims of biological
research and medical practice. Biomedical research into disease incorporates the work of a vast variety of life science specialists, whereas, in most parts of the world, to be licensed to practice pathology as medical specialty, one has to complete medical school
and secure a license to practice medicine. Structurally, the study of
disease is divided into many different fields that study or diagnose
markers for disease using methods and technologies particular to
specific scales, organs,
and tissue types. The information in this section mostly concerns
pathology as it regards common medical practice in these systems, but
each of these specialties is also the subject of voluminous pathology
research as regards the disease pathways of specific pathogens and
disorders that affect the tissues of these discrete organs or
structures.
Anatomical pathology
Anatomical pathology (Commonwealth) or anatomic pathology (United States) is a medical specialty that is concerned with the diagnosis of disease based on the gross, microscopic, chemical, immunologic and molecular examination of organs, tissues, and whole bodies (as in a general examination or an autopsy). Anatomical pathology is itself divided into subfields, the main divisions being surgical pathology, cytopathology, and forensic pathology.
Anatomical pathology is one of two main divisions of the medical
practice of pathology, the other being clinical pathology, the diagnosis
of disease through the laboratory
analysis of bodily fluids and tissues. Sometimes, pathologists practice
both anatomical and clinical pathology, a combination known as general
pathology.
A bone marrow smear from a case of erythroleukemia. The large cell in the top center is an abnormal erythroblast: it is multinucleated, with megaloblastoid nuclear chromatin This is diagnostic of erythroleukemia.
Cytopathology
Cytopathology (sometimes referred to as "cytology") is a branch of
pathology that studies and diagnoses diseases on the cellular level. It
is usually used to aid in the diagnosis of cancer, but also helps in the
diagnosis of certain infectious diseases and other inflammatory
conditions as well as thyroid lesions, diseases involving sterile body
cavities (peritoneal, pleural, and cerebrospinal), and a wide range of
other body sites. Cytopathology is generally used on samples of free
cells or tissue fragments (in contrast to histopathology, which studies
whole tissues) and cytopathologic tests are sometimes called smear tests
because the samples may be smeared across a glass microscope slide for
subsequent staining and microscopic examination. However, cytology
samples may be prepared in other ways, including cytocentrifugation.
Dermatopathology
A malignant melanoma can often be suspected from sight, but confirmation of the diagnosis or outright removal requires an excisional biopsy.
Dermatopathology is a subspecialty of anatomic pathology that focuses on the skin and the rest of the integumentary system
as an organ. It is unique, in that there are two paths a physician can
take to obtain the specialization. All general pathologists and
general dermatologists train in the pathology of the skin, so the term dermatopathologist
denotes either of these who has reached a certainly level of
accreditation and experience; in the USA, either a general pathologist
or a dermatologist
can undergo a 1 to 2 year fellowship in the field of dermatopathology.
The completion of this fellowship allows one to take a subspecialty
board examination, and becomes a board certified dermatopathologist.
Dermatologists are able to recognize most skin diseases based on their
appearances, anatomic distributions, and behavior. Sometimes, however,
those criteria do not lead to a conclusive diagnosis, and a skin biopsy
is taken to be examined under the microscope using usual histological
tests. In some cases, additional specialized testing needs to be
performed on biopsies, including immunofluorescence, immunohistochemistry, electron microscopy, flow cytometry, and molecular-pathologic analysis.
One of the greatest challenges of dermatopathology is its scope. More
than 1500 different disorders of the skin exist, including cutaneous
eruptions ("rashes") and neoplasms.
Therefore, dermatopathologists must maintain a broad base of knowledge
in clinical dermatology, and be familiar with several other specialty
areas in medicine.
Forensic pathology
Pathologist performing a human dissection of the abdominal and thoracic organs in an autopsy room.
Forensic pathology focuses on determining the cause of death by post-mortem examination
of a corpse or partial remains. An autopsy is typically performed by a
coroner or medical examiner, often during criminal investigations; in
this role, coroners
and medical examiners are also frequently asked to confirm the identity
of a corpse. The requirements for becoming a licensed practitioner of
forensic pathology varies from country to country (and even within a
given nation) but typically a minimal requirement is a medical doctorate
with a specialty in general or anatomical pathology with subsequent
study in forensic medicine. The methods forensic scientists use to
determine death include examination of tissue specimens to identify the
presence or absence of natural disease and other microscopic findings,
interpretations of toxicology
on body tissues and fluids to determine the chemical cause of
overdoses, poisonings or other cases involving toxic agents, and
examinations of physical trauma. Forensic pathology is a major component in the trans-disciplinary field of forensic science.
Histopathology
An instance of diagnosis via histopathology, this high-magnification micrograph of a section of cardiac tissue reveals advanced cardiac amyloidosis. This sample was attained through an autopsy.
Histopathology refers to the microscopic examination of various forms of human tissue.
Specifically, in clinical medicine, histopathology refers to the
examination of a biopsy or surgical specimen by a pathologist, after the
specimen has been processed and histological sections have been placed
onto glass slides.
This contrasts with the methods of cytopathology, which uses free
cells or tissue fragments. Histopathological examination of tissues
starts with surgery, biopsy,
or autopsy. The tissue is removed from the body of an organism and
then placed in a fixative that stabilizes the tissues to prevent decay.
The most common fixative is formalin, although frozen section fixing is also common.
To see the tissue under a microscope, the sections are stained with
one or more pigments. The aim of staining is to reveal cellular
components; counterstains are used to provide contrast. Histochemistry
refers to the science of using chemical reactions between laboratory
chemicals and components within tissue. The histological slides are
then interpreted diagnostically and the resulting pathology report
describes the histological findings and the opinion of the pathologist.
In the case of cancer, this represents the tissue diagnosis required
for most treatment protocols.
Neuropathology
This coronal cross-section of a brain reveals a significant arteriovenous malformation that occupies much of the parietal lobe.
Neuropathology is the study of disease of nervous system tissue,
usually in the form of either surgical biopsies or sometimes whole
brains in the case of autopsy. Neuropathology is a subspecialty of
anatomic pathology, neurology, and neurosurgery.
In many English-speaking countries, neuropathology is considered a
subfield of anatomical pathology. A physician who specializes in
neuropathology, usually by completing a fellowship after a residency in
anatomical or general pathology, is called a neuropathologist. In
day-to-day clinical practice, a neuropathologist is a consultant for
other physicians. If a disease of the nervous system is suspected, and
the diagnosis cannot be made by less invasive methods, a biopsy of
nervous tissue is taken from the brain or spinal cord to aid in
diagnosis. Biopsy is usually requested after a mass is detected by medical imaging.
With autopsies, the principal work of the neuropathologist is to help
in the post-mortem diagnosis of various conditions that affect the
central nervous system. Biopsies can also consist of the skin.
Epidermal nerve fiber density testing (ENFD) is a more recently
developed neuropathology test in which a punch skin biopsy is taken to identify small fiber neuropathies
by analyzing the nerve fibers of the skin. This test is becoming
available in select labs as well as many universities; it replaces the
traditional nerve biopsy test as less invasive.
Pulmonary pathology
Pulmonary pathology is a subspecialty of anatomic (and especially
surgical) pathology that deals with diagnosis and characterization of neoplastic and non-neoplastic diseases of the lungs and thoracic pleura. Diagnostic specimens are often obtained via bronchoscopic transbronchial biopsy, CT-guided percutaneous biopsy, or video-assisted thoracic surgery. These tests can be necessary to diagnose between infection, inflammation, or fibrotic conditions.
This tissue cross-section demonstrates the gross pathology of polycystic kidneys.
Renal pathology
Renal pathology is a subspecialty of anatomic pathology that deals with the diagnosis and characterization of disease of the kidneys. In a medical setting, renal pathologists work closely with nephrologists and transplant surgeons,
who typically obtain diagnostic specimens via percutaneous renal
biopsy. The renal pathologist must synthesize findings from traditional
microscope histology, electron microscopy, and immunofluorescence to obtain a definitive diagnosis. Medical renal diseases may affect the glomerulus, the tubules and interstitium, the vessels, or a combination of these compartments.
Surgical pathology
Surgical pathology is one of the primary areas of practice for most
anatomical pathologists. Surgical pathology involves the gross and
microscopic examination of surgical specimens, as well as biopsies
submitted by surgeons and non-surgeons such as general internists, medical subspecialists, dermatologists, and interventional radiologists. Often an excised tissue sample
is the best and most definitive evidence of disease (or lack thereof)
in cases where tissue is surgically removed from a patient. These
determinations are usually accomplished by a combination of gross (i.e.,
macroscopic) and histologic (i.e., microscopic) examination of the
tissue, and may involve evaluations of molecular properties of the
tissue by immunohistochemistry or other laboratory tests.
Brain biopsy under stereotaxy. A small part of the tumor is taken via a needle with a vacuum system.
There are two major types of specimens submitted for surgical
pathology analysis: biopsies and surgical resections. A biopsy is a
small piece of tissue removed primarily for surgical pathology analysis,
most often in order to render a definitive diagnosis. Types of biopsies
include core biopsies, which are obtained through the use of large-bore
needles, sometimes under the guidance of radiological techniques such
as ultrasound, CT scan, or magnetic resonance imaging. Incisional biopsies are obtained through diagnostic surgical procedures that remove part of a suspicious lesion,
whereas excisional biopsies remove the entire lesion, and are similar
to therapeutic surgical resections. Excisional biopsies of skin lesions and gastrointestinal polyps
are very common. The pathologist's interpretation of a biopsy is
critical to establishing the diagnosis of a benign or malignant tumor,
and can differentiate between different types and grades of cancer, as
well as determining the activity of specific molecular pathways in the
tumor. Surgical resection specimens are obtained by the therapeutic
surgical removal of an entire diseased area or organ (and occasionally
multiple organs). These procedures are often intended as definitive
surgical treatment of a disease in which the diagnosis is already known
or strongly suspected, but pathological analysis of these specimens
remains important in confirming the previous diagnosis.
Clinical pathology
Clinical pathology is a medical specialty that is concerned with the diagnosis of disease based on the laboratory analysis of bodily fluids such as blood and urine, as well as tissues, using the tools of chemistry, clinical microbiology, hematology and molecular pathology. Clinical pathologists work in close collaboration with medical technologists,
hospital administrations, and referring physicians. Clinical
pathologists learn to administer a number of visual and microscopic
tests and an especially large variety of tests of the biophysical properties of tissue samples involving Automated analysers and cultures.
Sometimes the general term "laboratory medicine specialist" is used to
refer to those working in clinical pathology, including medical
doctors, Ph.D.s and doctors of pharmacology. Immunopathology,
the study of an organism's immune response to infection, is sometimes
considered to fall within the domain of clinical pathology.
Hematopathology
Hematopathology is the study of diseases of blood cells (including constituents such as white blood cells, red blood cells, and platelets)
and the tissues, and organs comprising
the hematopoietic system. The term hematopoietic system refers to
tissues and organs that produce and/or primarily host hematopoietic
cells and includes bone marrow, the lymph nodes, thymus, spleen,
and other lymphoid tissues. In the United States, hematopathology is a
board certified subspecialty (licensed under the American Board of
Pathology) practiced by those physicians who have completed a general
pathology residency (anatomic, clinical, or combined) and an additional
year of fellowship training in hematology. The hematopathologist reviews
biopsies of lymph nodes, bone marrows and other tissues involved by an infiltrate
of cells of the hematopoietic system. In addition, the
hematopathologist may be in charge of flow cytometric and/or molecular
hematopathology studies.
Immunopathology
Immunopathology is a branch of clinical pathology that deals with an
organism’s immune response to a certain disease. When a foreign antigen
enters the body, there is either an antigen specific or nonspecific
response to it. These responses are the immune system fighting off the
foreign antigens, whether they are deadly or not. Immunopathology could
refer to how the foreign antigens cause the immune system to have a
response or problems that can arise from an organism’s own immune
response on itself. There are certain problems or faults in the immune
system that can lead to more serious illness or disease. These diseases
can come from one of the following problems. The first would be
Hypersensitivity reactions, where there would be a stronger immune
response than normal. There are four different types (type one, two,
three and four), all with varying types and degrees of an immune
response. The problems that arise from each type vary from small
allergic reactions to more serious illnesses such as tuberculosis or
arthritis. The second kind of complication in the immune system is
Autoimmunity, where the immune system would attack itself rather than
the antigen. Inflammation is a prime example of autoimmunity, as the
immune cells used are self-reactive. A few examples of autoimmune
diseases are Type 1 diabetes, Addison’s disease and Celiac disease. The
third and final type of complication with the immune system is
Immunodeficiency, where the immune system lacks the ability to fight off
a certain disease. The immune system’s ability to combat it is either
hindered or completely absent. The two types are Primary
Immunodeficiency, where the immune system is either missing a key
component or does not function properly, and Secondary Immunodeficiency,
where disease is obtained from an outside source, like radiation or
heat, and therefore cannot function properly. Diseases that can cause
immunodeficiency include HIV, AIDS and leukemia.
Radiation pathology
Radiation
pathology is study of the interaction between human tissues and
radiation, as well as the problems and diseases that can arise from the
use of radiation. When human tissue is exposed to radiation, it can be
genetically altered and deformed; in turn, this could lead to a variety
of illnesses that could be minor or deadly.
Molecular pathology
Molecular pathology is focused upon the study and diagnosis of
disease through the examination of molecules within organs, tissues or bodily fluids.
Molecular pathology is multidisciplinary by nature and shares some
aspects of practice with both anatomic pathology and clinical pathology,
molecular biology, biochemistry, proteomics and genetics.
It is often applied in a context that is as much scientific as
directly medical and encompasses the development of molecular and
genetic approaches to the diagnosis and classification of human
diseases, the design and validation of predictive biomarkers for
treatment response and disease progression, and the susceptibility of
individuals of different genetic constitution to particular disorders.
The crossover between molecular pathology and epidemiology is represented by a related field "molecular pathological epidemiology". Molecular pathology is commonly used in diagnosis of cancer and
infectious diseases. Molecular Pathology is primarily used to detect
cancers such as melanoma, brainstem glioma, brain tumors as well as many
other types of cancer and infectious diseases.
Techniques are numerous but include quantitative polymerase chain
reaction (qPCR), multiplex PCR, DNA microarray, in situ hybridization,
DNA sequencing, antibody based immunofluorescence tissue assays,
molecular profiling of pathogens, and analysis of bacterial genes for antimicrobial resistance. Techniques used are based on analyzing samples of DNA and RNA. Pathology is widely used for gene therapy and disease diagnosis.
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Many conditions, such as this case of geographic tongue, can be diagnosed partly on gross examination, but may be confirmed with tissue pathology.
Oral and maxillofacial pathology
Oral and Maxillofacial Pathology is one of nine dental specialties recognized by the American Dental Association, and is sometimes considered a specialty of both dentistry and pathology.
Oral Pathologists must complete three years of post doctoral training
in an accredited program and subsequently obtain diplomate status from
the American Board of Oral and Maxillofacial Pathology. The specialty
focuses on the diagnosis, clinical management and investigation of
diseases that affect the oral cavity and surrounding maxillofacial
structures including but not limited to odontogenic, infectious, epithelial, salivary gland, bone and soft tissue pathologies. It also significantly intersects with the field of dental pathology. Although concerned with a broad variety of diseases of the oral cavity, they have roles distinct from otorhinolaryngologists ("ear, nose, and throat" specialists), and speech pathologists, the latter of which helps diagnose many neurological or neuromuscular conditions relevant to speech phonology or swallowing. Owing to the availability of the oral cavity
to non-invasive examination, many conditions in the study of oral
disease can be diagnosed, or at least suspected, from gross examination,
but biopsies, cell smears, and other tissue analysis remain important
diagnostic tools in oral pathology.
Medical training and accreditation
Individual nations vary some in the medical licensing required of pathologists. In the United States, pathologists are physicians (D.O. or M.D.)
that have completed a four-year undergraduate program, four years of
medical school training, and three to four years of postgraduate
training in the form of a pathology residency. Training may be within two primary specialties, as recognized by the American Board of Pathology: anatomical Pathology and clinical Pathology, each of which requires separate board certification. The American Osteopathic Board of Pathology also recognizes four primary specialties: anatomic pathology, dermatopathology, forensic pathology, and laboratory medicine.
Pathologists may pursue specialised fellowship training within one or
more subspecialties of either anatomical or clinical pathology. Some of
these subspecialties permit additional board certification, while others
do not.
An anatomical pathology instructor uses a microscope with multiple eyepieces to instruct students in diagnostic microscopy.
In the United Kingdom, pathologists are physicians licensed by the UK General Medical Council. The training to become a pathologist is under the oversight of the Royal College of Pathologists.
After four to six years of undergraduate medical study, trainees
proceed to a two-year foundation program. Full-time training in
histopathology currently lasts between five and five and a half years
and includes specialist training in surgical pathology, cytopathology,
and autopsy pathology. It is also possible to take a Royal College of Pathologists
diploma in forensic pathology, dermatopathology, or cytopathology,
recognising additional specialist training and expertise and to get
specialist accreditation in forensic pathology, pediatric pathology, and neuropathology. All postgraduate medical training and education in the UK is overseen by the General Medical Council.
In France, Pathology is separate in two distinct specialties,
anatomical pathology and clinical pathology. Residencies for both lasts
four years. Residency in anatomical pathology is open to physicians
only, while clinical pathology is open to both physicians and pharmacists.
At the end of the second year of clinical pathology residency,
residents can choose between general clinical pathology and a
specialization in one of the disciplines, but they can not practice
anatomical pathology, nor can anatomical pathology residents practice
clinical pathology.
Overlap with other diagnostic medicine
Though separate fields in terms of medical practice, a number of
areas of inquiry in medicine and
medical science either overlap greatly with general pathology, work in
tandem with it, or contribute significantly to the understanding of the
pathology of a given disease or its course in an individual. As a
significant portion of all general pathology practice is concerned with cancer, the practice of oncology is deeply tied to, and dependent upon, the work of both anatomical and clinical pathologists. Biopsy, resection and blood tests are all examples of pathology work that is essential for the diagnoses of many kinds of cancer and for the staging of cancerous masses.
In a similar fashion, the tissue and blood analysis techniques of
general pathology are of central significance to the investigation of
serious infectious disease and as such inform significantly upon the fields of epidemiology, etiology, immunology, and parasitology.
General pathology methods are of great importance to biomedical
research into disease, wherein they are sometimes referred to as "experimental" or "investigative" pathology.
Medical imaging
is the generating of visual representations of the interior of a body
for clinical analysis and medical intervention. Medical imaging reveals
details of internal
physiology that help medical professionals plan appropriate treatments
for tissue infection and trauma. Medical imaging is also central in
supplying the biometric data necessary to establish baseline features of anatomy and physiology
so as to increase the accuracy with which early or fine-detail
abnormalities are detected. These diagnostic techniques are often
performed in combination with general pathology procedures and are
themselves often essential to developing new understanding of the pathogenesis
of a given disease and tracking the progress of disease in specific
medical cases. Examples of important subdivisions in medical imaging
include radiology (which uses the imaging technologies of X-ray radiography) magnetic resonance imaging, medical ultrasonography (or ultrasound), endoscopy, elastography, tactile imaging, thermography, medical photography, nuclear medicine and functional imaging techniques such as positron emission tomography. Though they do not strictly relay images, readings from diagnostics tests involving electroencephalography, magnetoencephalography, and electrocardiography often give hints as to the state and function of certain tissues in the brain and heart respectively.
Psychopathology
Psychopathology is the study of mental illness, particularly of severe disorders. Informed heavily by both psychology and neurology, its purpose is to classify mental illness, elucidate its underlying causes, and guide clinical psychiatric
treatment accordingly. Although diagnosis and classification of mental
norms and disorders is largely the purview of psychiatry—the results of
which are guidelines such as the Diagnostic and Statistical Manual of Mental Disorders, which attempt to classify mental disease mostly on behavioural evidence, though not without controversy—the field is also heavily, and increasingly, informed upon by neuroscience and other of the biological cognitive sciences.
Mental or social disorders or behaviors seen as generally unhealthy
or excessive in a given individual, to the point where they cause harm
or severe disruption to the sufferer's lifestyle, are often called
"pathological" (e.g., pathological gambling or pathological liar).
History
The advent of the microscope was one of the major developments in the history of pathology. Here researchers at the Centers for Disease Control in 1978 examine cultures containing Legionella pneumophila, the pathogen responsible for Legionnaire's disease.
The study of pathology, including the detailed examination of the
body, including dissection and inquiry into specific maladies, dates
back to antiquity. Rudimentary understanding of many conditions was
present in most early societies and is attested to in the records of the
earliest historical societies, including those of the Middle East, India, and China. By the Hellenic period of ancient Greece, a concerted causal study of disease was underway, with many notable early physicians (such as Hippocrates, for whom the modern Hippocratic Oath is named) having developed methods of diagnosis and prognosis for a number of diseases.The medical practices of the Romans and those of the Byzantines
continued from these Greek roots, but, as with many areas of scientific
inquiry, growth in understanding of medicine stagnated some after the Classical Era,
but continued to slowly develop throughout numerous cultures. Notably,
many advances were made in the medieval era of Islam, during which numerous texts of complex pathologies were developed, also based on the Greek tradition.
Even so, growth in complex understanding of disease mostly languished
until knowledge and experimentation again began to proliferate in the Renaissance, Enlightenment, and Baroque
eras, following the resurgence of the empirical method at new centers
of scholarship. By the 17th century, the study of microscopy was
underway and examination of tissues had led British Royal Society member Robert Hooke to coin the word "cell", setting the stage for later germ theory.
Modern pathology began to develop as a distinct field of inquiry during the 19th Century through natural philosophers
and physicians that studied disease and the informal study of what they
termed “pathological anatomy” or “morbid anatomy”. However, pathology
as a formal area of specialty was not fully developed until the late
19th and early 20th centuries, with the advent of detailed study of microbiology.
In the 19th century, physicians had begun to understand that
disease-causing pathogens, or "germs" (a catch-all for disease-causing,
or pathogenic, microbes, such as bacteria, viruses, fungi, amoebae, molds, protists, and prions) existed and were capable of reproduction and multiplication, replacing earlier beliefs in humors
or even spiritual agents, that had dominated for much of the previous
1,500 years in European medicine. With the new understanding of
causative agents, physicians began to compare the characteristics of one
germ’s symptoms as they developed within an affected individual to
another germ’s characteristics and symptoms. This realization led to the
foundational understanding that diseases are able to replicate
themselves, and that they can have many profound and varied effects on
the human host. To determine causes of diseases, medical experts used
the most common and widely accepted assumptions or symptoms of their
times, a general principal of approach that persists into modern
medicine.
Modern medicine was particularly advanced by further developments of the microscope to analyze tissues, to which Rudolf Virchow gave a significant contribution, leading to a slew of research developments.
By the late 1920s to early 1930s pathology was deemed a medical specialty. Combined with developments in the understanding of general physiology,
by the beginning of the 20th century, the study of pathology had begun
to split into a number of rarefied fields and resulting in the
development of large number of modern specialties within pathology and
related disciplines of diagnostic medicine.
Non-humans
This field post-mortem of a ewe has revealed lesions consistent with acute haemolytic pneumonia, possibly due to Pasteurella haemolytica.
Although the vast majority of lab work and research in pathology
concerns the development of disease in humans, pathology is of
significance throughout the biological sciences. Two main catch-all
fields exist to represent most complex organisms capable of serving as
host to a pathogen or other form of disease: veterinary pathology
(concerned with all non-human species of kingdom of Animalia) and phytopathology, which studies disease in plants.
Veterinary
Veterinary pathology covers a vast array of species, but with a
significantly smaller number of practitioners, so understanding of
disease in non-human animals, especially as regards veterinary practice,
varies considerably by species. Nonetheless, significant amounts of
pathology research are conducted on animals, for two primary reasons: 1)
The origins of diseases are typically zoonotic
in nature, and many infectious pathogens have animal vectors and, as
such, understanding the mechanisms of action for these pathogens in
non-human hosts is essential to the understanding and application of epidemiology
and 2) those animals that share physiological and genetic traits with
humans can be used as surrogates for the study of the disease and
potential treatments as well as the effects of various synthetic products. For this reason, as well as their roles as livestock and companion animals, mammals
generally have the largest body of research in veterinary pathology.
Animal testing remains a controversial practice, even in cases where it
is used to research treatment for human disease.
As in human medical pathology, the practice of veterinary pathology is
customarily divided into the two main fields of anatomical and clinical
pathology.
A tobacco plant infected with the tobacco mosaic virus
Plants
Although the pathogens and their mechanics differ greatly from those
of animals, plants are subject to a wide variety of diseases, including
those caused by fungi, oomycetes, bacteria, viruses, viroids, virus-like organisms, phytoplasmas, protozoa, nematodes and parasitic plants. Damage caused by insects, mites, vertebrate, and other small herbivores is not considered a part of the domain of plant pathology. The field is deeply connected to plant disease epidemiology and the horticulture of species that are of high importance to the human diet or other uses.
