programmed cell death

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Related to Cellular Death: apoptosis, Apoptotic, somatic death


the cessation of all physical and chemical processes that invariably occurs in all living organisms. (See also dying.) There is at present no standardized diagnosis of clinical death or precise definition of human death. The most widely known and commonly accepted means of determining death evolved from several medical conferences held in the late 1960s for the purpose of defining irreversible coma or nonfunctioning brain as a new criterion for death. The indications of deep irreversible coma (or brain death) are (1) absolute unresponsiveness to externally applied stimuli; (2) cessation of movement and breathing, including no spontaneous breathing for three minutes after an artificial respirator has been turned off; and (3) complete absence of cephalic reflexes. The pupils of the eyes must be dilated and unresponsive to direct light.

Use of the electroencephalogram is also recommended as being of value in confirmation of irreversible coma or death. If there is a flat electroencephalographic reading at the time of apparent death and a second flat reading 24 hours later, then the patient may be declared dead.

There are two exceptions to the above criteria. These are in regard to patients exhibiting marked hypothermia (body temperature below 32.2°C), and those suffering from severe central nervous system depression as a result of drug overdose.

It is recognized that the above criteria are limited in that the notion of irreversibility is not readily agreed upon and may take on new meaning as medical technology advances. The criteria are especially helpful as complements to the traditional criteria of absence of heart beat and lack of spontaneous respiration as indications of death.

In 1981, a Presidential Commission for the Study of Ethical Problems in Medicine and Biomedical and Behavioral Research strongly recommended that all of the United States recognize the cessation of brain function as a definition of death, even in cases in which life-support systems could maintain respiratory and circulatory functions by artificial means.
activation-induced cell death (AICD) recognition and deletion of T lymphocytes that have been activated and so induced to proliferate. T lymphocytes are activated when a foreign agent is perceived, and AICD thereby prevents them from overgrowth. It is particularly important for regulation of lymphocytes that recognize self antigens.
black death bubonic plague; see plague.
brain death (cerebral death) see brain death.
clinical death the absence of heart beat (no pulse can be felt) and cessation of breathing.
cot death (crib death) sudden infant death syndrome (SIDS).
programmed cell death the theory that particular cells are programmed to die at specific sites and at specific stages of development.


(ap'op-tō'sis, ap'ō-tō'sis), In the diphthong pt, the p is properly silent only at the begining of a word. Many speakers in the U.S. nonetheless silence it in this word.
Programmed cell death; deletion of individual cells by fragmentation into membrane-bound particles, which are phagocytized by other cells.
[G. a falling or dropping off, fr. apo, off, + ptosis, a falling]

Whereas some cells (for example, cardiac and skeletal muscle fibers, CNS neurons) last a lifetime, others (for example, epithelial and glandular cells, erythrocytes) have limited life-spans, at the end of which they are genetically programmed for self-destruction by apoptosis, usually to be replaced by others formed by mitosis from surviving cells. Apoptosis also plays an essential role in morphogenesis and tissue homeostasis by eliminating transitory organs and tissues (for example, pronephros and mesonephros) and cells formed in excess of bodily needs during embryogenesis, as well as cells that have been damaged or virally infected. Cells in tissue cultures spontaneously undergo apoptosis after about 50 cell divisions. In contrast to cell death caused by injury, infection, or circulatory impairment, apoptosis elicits no inflammatory response in adjacent cells and tissues. Features of apoptosis detectable by histologic and histochemical methods include cell shrinkage, due chiefly to dehydration; increased membrane permeability, with a rise in intracellular calcium and a fall in pH; nuclear and cytoplasmic condensation; endolytic cleavage of nuclear DNA into oligonucleosomal fragments; and ultimately formation of apoptotic bodies, which are absorbed and removed by macrophages. Besides being due to genetic programming, apoptosis can be induced by injury to cellular DNA, as by irradiation and some cytotoxic agents used to treat cancer. It can be suppressed by naturally occurring factors (for example, cytokines) and by some drugs (for example, protease inhibitors). Apoptosis typically does not occur in malignant cells. Such cells therefore escape the destiny of their nonmalignant precursor cells and are said to be immortal. Immortalization can occur in various ways. The BCL2 gene, present in many cancers, directs the production of an enzyme that blocks apoptosis and immortalizes affected cells. Injury to DNA normally triggers apoptosis by activating the p53 tumor suppressor gene, which is missing or mutated in about one half of all human cancers. Cells that lack this gene can survive chemotherapy and irradiation intended to destroy cancer cells. Failure of apoptosis to occur is also involved in some degenerative diseases, including lupus erythematosus, and may be responsible for cellular damage caused by certain viruses, including HIV. Apoptosis has thus far been observed only in animal cells.

programmed cell death



An intrinsic, highly complex programme of auto-orchestrated cell death, which is as complex and important as proliferation. Apoptosis is morphologically characterised by chromatin condensation and DNA degradation, and is a mechanism used by the immune system for antigen-induced clonal deletion of cortical thymocytes (i.e., immune tolerance). It is the most common form of eukaryotic cell death in embryogenesis, metamorphosis, tissue atrophy and tumour regression; it is induced by cytotoxic T cells, NK and killer cells, lymphotoxins, Ca2+, glucocorticoids, withdrawal of interleukins, heat shock, viral infection, oxidants, free radicals, by some monoclonal antibodies (e.g., APO-1), chemotherapeutic agents (e.g., bleomycin, cisplatin, cytosine arabinoside, methotrexate, vincristine and others), gamma radiation and UV light. Cells that die by apoptosis do not usually elicit the inflammatory responses seen in necrosis.

Apoptosis is inhibited by physiologic factors (growth factors), extracellular matrix, CD40 ligand, neutral amino acids, zinc, sex hormones, viral genes (e.g., adenovirus E1B, baculovirus p35, EBV LMP-1 and others) and pharmacologic agents (e.g., inhibitors of calpain and cysteine protease and tumour promoters, such as PMA and phenobarbital).

Apoptosis and disease
Defects in apoptosis have been pathogenically linked to AIDS, Alzheimer’s disease and other neurodegenerative phenomena, autoimmune disease, cancer, ischaemic injury, liver toxicity (.g., by alcohol), myelodysplastic syndrome, viral infections and other conditions.


Programmed cell death; deletion of individual cells by fragmentation into membrane-bound particles, which are phagocytized by other cells.
Synonym(s): programmed cell death.
[G. a falling or dropping off, fr. apo, off, + ptosis, a falling]

programmed cell death



Programmed cell death; deletion of individual cells by fragmentation into membrane-bound particles, which are phagocytized by other cells.
Synonym(s): programmed cell death.
[G. a falling or dropping off, fr. apo, off, + ptosis, a falling]

programmed cell death

proposed system of cell death, often including poly(ADP)-ribosylation, ensures that a cell will not survive if it is so badly damaged that its recovery would harm the organism. See also apoptosis.
References in periodicals archive ?
The free radicals likely play a role in cellular death during reperfusion injury (Reddy & Labhasetwar, 2009).
Because continuing oxidative stress damages the retina over time and activation of Nrf2 is not expected to reverse cellular death, preventing the progress of dry AMD might be a more promising target, as in the case of the AREDS study.
Necrosis is a process of cellular death and tissue damage initiated typically by the molecules of inflammation.
In the development of the aerenchyma of the expansigeny type, found in the families Polygonaceae and Pontederiaceae, the expansion of intercellular spaces originates gaps without causing collapse or cellular death.
It should be remembered that every death which occurs due to one or the other cause amongst cardiorespiratory failure, cardiac failure, respiratory failure means simply the cessation of circulation and respiration leading to somatic and cellular death.
The frequent disruption of oxygen leads to cellular death and also incites inflammation, says Ronald Harper, PhD, Distinguished Professor of Neurobiology at UCLA's David Geffen School of Medicine.
After this "point of no return" most probably due the combined damage by ROS to cellular membranes, transport systems and mitochondria, cellular death is inevitably initiated and no longer under control by antioxidants.
Moreover, in conditions as disparate as ischemic heart disease, inflammatory bowel disease, cataract formation, immune-mediated kidney damage, asthma, cancer, diabetes mellitus, and infertility, OS is being increasingly recognised as a key common pathway for cellular death and dysfunction, and a potentially important target for therapeutic intervention.
The teratogenic mechanism of cyclophosphamide action involves induction of cellular death in cells of rapid proliferation by limitation of DNA synthesis.
Among the adverse effects observed were mitochondrial structural decomposition, mitochondrial swelling due to increased membrane porosity and rupturing, increased production of free radicals, and induction of cellular death.
This is crucial to understanding photosensitivity and lupus because TNF-alpha has been shown to stimulate apoptosis, the process of cellular death.
Cellular death seems a fundamental axis in the embryo organization since its early stages: in a mouse blastocyst, relevant cell death is observed in vivo, suggesting that it plays an important role in normal development.