General pathology
Encyclopedia
General pathology, also called investigative pathology, experimental pathology or theoretical pathology, is a broad and complex scientific field
which seeks to understand the mechanisms of injury to cells
and tissues
, as well as the body's means of responding to and repairing injury. Areas of study include cellular adaptation to injury, necrosis
, inflammation
, wound healing
and neoplasia
. It forms the foundation of pathology
, the application of this knowledge to diagnose diseases in humans and animals
.
The term "general pathology" is also used to describe the practice of both anatomical
and clinical pathology
.
, infection
, poison
ing, loss of blood flow
, autoimmunity
, inherited or acquired genetic damage, or errors of development
. One common theme in pathology is the way in which the body's responses to injury, while evolved to protect health, can also contribute in some ways to disease processes.
Cells and tissues may respond to injury and stress by specific mechanisms, which may vary according to the cell types and nature of the injury. In the short term, cells may activate specific genetic programs to protect their vital protein
s and organelle
s from heat shock
or hypoxia
, and may activate DNA repair
pathways to repair damage to chromosomes from radiation
or chemicals. Hyperplasia
is a long-term adaptive response of cell division and multiplication
, which can increase the ability of a tissue to compensate for an injury. For example, repeated irritation to the skin can cause a protective thickening
due to hyperplasia of the epidermis. Hypertrophy
is an increase in the size of cells in a tissue in response to stress, an example being hypertrophy of muscle cells in the heart
in response to increased resistance to blood flow as a result of narrowing of the heart's outflow valve. Metaplasia
occurs when repeated damage to the cellular lining of an organ triggers its replacement by a different cell type.
is the irreversible destruction of cells as a result of severe injury in a setting where the cell is unable to activate the needed metabolic pathways for survival or orderly degeneration. This is often due to external pathologic factors, such as toxins or loss of oxygen supply. Milder stresses may lead to a process called reversible cell injury, which mimics the cell swelling and vacuolization seen early in the necrotic process, but in which the cell is able to adapt and survive. In necrosis, the components of degenerating cells leak out, potentially contributing to inflammation and further damage. Apoptosis
, in contrast, is a regulated, orderly degeneration of the cell which occurs in the settings of both injury and normal physiological processes.
Inflammation
is a particularly important and complex reaction to tissue injury, and is particularly important in fighting infection
. Acute inflammation is generally a non-specific response triggered by the injured tissue cells themselves, as well as specialized cells of the innate immune system
and previously developed adaptive immune
mechanisms. A localized acute inflammatory response triggers vascular changes in the injured area, recruits pathogen
-fighting neutrophils, and begins the process of developing a new adaptive immune response. Chronic inflammation occurs when the acute response fails to entirely clear the inciting factor. While chronic inflammation can lay a positive role in containing a continuing infectious hazard, it can also lead to progressive tissue damage, as well as predisposing (in some cases) to the development of cancer
.
, is triggered by inflammation. The process may proceed even before the resolution of a precipitating insult, through the formation of granulation tissue
. Healing involves the proliferation of connective tissue
cells and blood vessel
-forming cells as a result of hormonal growth signals. While healing is a critical adaptive response, an aberrant healing response can lead to progressive fibrosis
, contractures, or other changes which can compromise function.
, or "new growth," is a proliferation of cells which is independent of any physiological process. The most familiar examples of neoplasia are benign tumors and cancer
s. Neoplasia results from genetic changes which cause cells to activate genetic programs inappropriately. Dysplasia
is an early sign of a neoplastic process in a tissue, and is marked by persistence of immature, poorly differentiated cell forms. Interestingly, there are many similarities in the gene pathways activated in cancer cells, and those activated in cells involved in wound healing and inflammation.
Science
Science is a systematic enterprise that builds and organizes knowledge in the form of testable explanations and predictions about the universe...
which seeks to understand the mechanisms of injury to cells
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
and tissues
Tissue (biology)
Tissue is a cellular organizational level intermediate between cells and a complete organism. A tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function. These are called tissues because of their identical functioning...
, as well as the body's means of responding to and repairing injury. Areas of study include cellular adaptation to injury, necrosis
Necrosis
Necrosis is the premature death of cells in living tissue. Necrosis is caused by factors external to the cell or tissue, such as infection, toxins, or trauma. This is in contrast to apoptosis, which is a naturally occurring cause of cellular death...
, inflammation
Inflammation
Inflammation is part of the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. Inflammation is a protective attempt by the organism to remove the injurious stimuli and to initiate the healing process...
, wound healing
Wound healing
Wound healing, or cicatrisation, is an intricate process in which the skin repairs itself after injury. In normal skin, the epidermis and dermis exists in a steady-state equilibrium, forming a protective barrier against the external environment...
and neoplasia
Neoplasia
Neoplasm is an abnormal mass of tissue as a result of neoplasia. Neoplasia is the abnormal proliferation of cells. The growth of neoplastic cells exceeds and is not coordinated with that of the normal tissues around it. The growth persists in the same excessive manner even after cessation of the...
. It forms the foundation of pathology
Pathology
Pathology is the precise study and diagnosis of disease. The word pathology is from Ancient Greek , pathos, "feeling, suffering"; and , -logia, "the study of". Pathologization, to pathologize, refers to the process of defining a condition or behavior as pathological, e.g. pathological gambling....
, the application of this knowledge to diagnose diseases in humans and animals
Veterinary pathology
Veterinary pathologists are doctors of veterinary medicine who specialize in the diagnosis of diseases through the examination of animal tissue and body fluids. Like medical pathology, veterinary pathology is divided into two branches, anatomical pathology and clinical pathology. Veterinary...
.
The term "general pathology" is also used to describe the practice of both anatomical
Anatomical pathology
Anatomical pathology or Anatomic pathology 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...
and clinical pathology
Clinical pathology
Clinical pathology , Laboratory Medicine , Clinical analysis or Clinical/Medical Biology , is a medical specialty that is concerned with the diagnosis of disease based on the laboratory analysis of bodily fluids, such as...
.
Adaptation to injury
Disease processes may be incited or exacerbated by a variety of external and internal influences, including traumaPhysical trauma
Trauma refers to "a body wound or shock produced by sudden physical injury, as from violence or accident." It can also be described as "a physical wound or injury, such as a fracture or blow." Major trauma can result in secondary complications such as circulatory shock, respiratory failure and death...
, infection
Infection
An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...
, poison
Poison
In the context of biology, poisons are substances that can cause disturbances to organisms, usually by chemical reaction or other activity on the molecular scale, when a sufficient quantity is absorbed by an organism....
ing, loss of blood flow
Ischemia
In medicine, ischemia is a restriction in blood supply, generally due to factors in the blood vessels, with resultant damage or dysfunction of tissue. It may also be spelled ischaemia or ischæmia...
, autoimmunity
Autoimmunity
Autoimmunity is the failure of an organism to recognize its own constituent parts as self, which allows an immune response against its own cells and tissues. Any disease that results from such an aberrant immune response is termed an autoimmune disease...
, inherited or acquired genetic damage, or errors of development
Developmental biology
Developmental biology is the study of the process by which organisms grow and develop. Modern developmental biology studies the genetic control of cell growth, differentiation and "morphogenesis", which is the process that gives rise to tissues, organs and anatomy.- Related fields of study...
. One common theme in pathology is the way in which the body's responses to injury, while evolved to protect health, can also contribute in some ways to disease processes.
Cells and tissues may respond to injury and stress by specific mechanisms, which may vary according to the cell types and nature of the injury. In the short term, cells may activate specific genetic programs to protect their vital protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
s and organelle
Organelle
In cell biology, an organelle is a specialized subunit within a cell that has a specific function, and is usually separately enclosed within its own lipid bilayer....
s from heat shock
Heat shock
In biochemistry, heat shock is the effect of subjecting a cell to a higher temperature than that of the ideal body temperature of the organism from which the cell line was derived.-Heat shock response:...
or hypoxia
Hypoxia (medical)
Hypoxia, or hypoxiation, is a pathological condition in which the body as a whole or a region of the body is deprived of adequate oxygen supply. Variations in arterial oxygen concentrations can be part of the normal physiology, for example, during strenuous physical exercise...
, and may activate DNA repair
DNA repair
DNA repair refers to a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. In human cells, both normal metabolic activities and environmental factors such as UV light and radiation can cause DNA damage, resulting in as many as 1...
pathways to repair damage to chromosomes from radiation
Electromagnetic radiation
Electromagnetic radiation is a form of energy that exhibits wave-like behavior as it travels through space...
or chemicals. Hyperplasia
Hyperplasia
Hyperplasia means increase in number of cells/proliferation of cells. It may result in the gross enlargement of an organ and the term is sometimes mixed with benign neoplasia/ benign tumor....
is a long-term adaptive response of cell division and multiplication
Cell growth
The term cell growth is used in the contexts of cell development and cell division . When used in the context of cell division, it refers to growth of cell populations, where one cell grows and divides to produce two "daughter cells"...
, which can increase the ability of a tissue to compensate for an injury. For example, repeated irritation to the skin can cause a protective thickening
Hyperkeratosis
Hyperkeratosis is thickening of the stratum corneum, often associated with a qualitative abnormality of the keratin, and also usually accompanied by an increase also in the granular layer...
due to hyperplasia of the epidermis. Hypertrophy
Hypertrophy
Hypertrophy is the increase in the volume of an organ or tissue due to the enlargement of its component cells. It should be distinguished from hyperplasia, in which the cells remain approximately the same size but increase in number...
is an increase in the size of cells in a tissue in response to stress, an example being hypertrophy of muscle cells in the heart
Heart
The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...
in response to increased resistance to blood flow as a result of narrowing of the heart's outflow valve. Metaplasia
Metaplasia
Metaplasia is the reversible replacement of one differentiated cell type with another mature differentiated cell type. The change from one type of cell to another may generally be a part of normal maturation process or caused by some sort of abnormal stimulus...
occurs when repeated damage to the cellular lining of an organ triggers its replacement by a different cell type.
Cell death
NecrosisNecrosis
Necrosis is the premature death of cells in living tissue. Necrosis is caused by factors external to the cell or tissue, such as infection, toxins, or trauma. This is in contrast to apoptosis, which is a naturally occurring cause of cellular death...
is the irreversible destruction of cells as a result of severe injury in a setting where the cell is unable to activate the needed metabolic pathways for survival or orderly degeneration. This is often due to external pathologic factors, such as toxins or loss of oxygen supply. Milder stresses may lead to a process called reversible cell injury, which mimics the cell swelling and vacuolization seen early in the necrotic process, but in which the cell is able to adapt and survive. In necrosis, the components of degenerating cells leak out, potentially contributing to inflammation and further damage. Apoptosis
Apoptosis
Apoptosis is the process of programmed cell death that may occur in multicellular organisms. Biochemical events lead to characteristic cell changes and death. These changes include blebbing, cell shrinkage, nuclear fragmentation, chromatin condensation, and chromosomal DNA fragmentation...
, in contrast, is a regulated, orderly degeneration of the cell which occurs in the settings of both injury and normal physiological processes.
Inflammation
Inflammation
Inflammation is part of the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. Inflammation is a protective attempt by the organism to remove the injurious stimuli and to initiate the healing process...
is a particularly important and complex reaction to tissue injury, and is particularly important in fighting infection
Infection
An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...
. Acute inflammation is generally a non-specific response triggered by the injured tissue cells themselves, as well as specialized cells of the innate immune system
Innate immune system
The innate immune system, also known as non-specific immune system and secondary line of defence, comprises the cells and mechanisms that defend the host from infection by other organisms in a non-specific manner...
and previously developed adaptive immune
Adaptive immune system
The adaptive immune system is composed of highly specialized, systemic cells and processes that eliminate or prevent pathogenic growth. Thought to have arisen in the first jawed vertebrates, the adaptive or "specific" immune system is activated by the “non-specific” and evolutionarily older innate...
mechanisms. A localized acute inflammatory response triggers vascular changes in the injured area, recruits pathogen
Pathogen
A pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...
-fighting neutrophils, and begins the process of developing a new adaptive immune response. Chronic inflammation occurs when the acute response fails to entirely clear the inciting factor. While chronic inflammation can lay a positive role in containing a continuing infectious hazard, it can also lead to progressive tissue damage, as well as predisposing (in some cases) to the development of cancer
Cancer
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...
.
Tissue repair
Tissue repair, as seen in wound healingWound healing
Wound healing, or cicatrisation, is an intricate process in which the skin repairs itself after injury. In normal skin, the epidermis and dermis exists in a steady-state equilibrium, forming a protective barrier against the external environment...
, is triggered by inflammation. The process may proceed even before the resolution of a precipitating insult, through the formation of granulation tissue
Granulation tissue
Granulation tissue is the perfused, fibrous connective tissue that replaces a fibrin clot in healing wounds. Granulation tissue typically grows from the base of a wound and is able to fill wounds of almost any size it heals...
. Healing involves the proliferation of connective tissue
Connective tissue
"Connective tissue" is a fibrous tissue. It is one of the four traditional classes of tissues . Connective Tissue is found throughout the body.In fact the whole framework of the skeleton and the different specialized connective tissues from the crown of the head to the toes determine the form of...
cells and blood vessel
Blood vessel
The blood vessels are the part of the circulatory system that transports blood throughout the body. There are three major types of blood vessels: the arteries, which carry the blood away from the heart; the capillaries, which enable the actual exchange of water and chemicals between the blood and...
-forming cells as a result of hormonal growth signals. While healing is a critical adaptive response, an aberrant healing response can lead to progressive fibrosis
Fibrosis
Fibrosis is the formation of excess fibrous connective tissue in an organ or tissue in a reparative or reactive process. This is as opposed to formation of fibrous tissue as a normal constituent of an organ or tissue...
, contractures, or other changes which can compromise function.
Neoplasia
NeoplasiaNeoplasia
Neoplasm is an abnormal mass of tissue as a result of neoplasia. Neoplasia is the abnormal proliferation of cells. The growth of neoplastic cells exceeds and is not coordinated with that of the normal tissues around it. The growth persists in the same excessive manner even after cessation of the...
, or "new growth," is a proliferation of cells which is independent of any physiological process. The most familiar examples of neoplasia are benign tumors and cancer
Cancer
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...
s. Neoplasia results from genetic changes which cause cells to activate genetic programs inappropriately. Dysplasia
Dysplasia
Dysplasia , is a term used in pathology to refer to an abnormality of development. This generally consists of an expansion of immature cells, with a corresponding decrease in the number and location of mature cells. Dysplasia is often indicative of an early neoplastic process...
is an early sign of a neoplastic process in a tissue, and is marked by persistence of immature, poorly differentiated cell forms. Interestingly, there are many similarities in the gene pathways activated in cancer cells, and those activated in cells involved in wound healing and inflammation.