Non-exhaustive list of definitions of terms used in gerontology and in

Aging: a progressive deterioration of physiological function, an intrinsic age-related process of loss of viability and increase in vulnerability. In humans, aging is characterized by a complex phenotype.

Allele: one of two or more variant forms of a gene.

Aphagy: inability to feed oneself due to anatomical deficiencies, common in the adult phase of some species of animals.

Apoptosis: programmed cell death.

Antagonistic pleiotropy: theory by George Williams that explains the existence of aging by the existence of genes beneficial early in life but harmful at later stages.

Autophagy: digestion of the cell's own components; it has been implicated in aging.

Biogerontology: the scientific study of the biological process of aging.

Caloric restriction (CR): diet regime consisting of eating considerably fewer calories, without malnutrition, that has been considered as a potential method to delay aging.

Cellular or clonal senescence: see replicative senescence.

Cellular immortality: the ability of certain cell populations, like most cancer cells, to divide indefinitely in culture.

Demography: the statistical study of populations; human aging is characterized by demographic aging.

Developmental theory of aging (DevAge): theory arguing that aging is an extension of developmental mechanisms.

Diphyodont: an animal that develops two successive sets of teeth, common in most mammals.

Diploid: a cell with two sets of chromosomes.

Disposable soma theory: theory by Thomas Kirkwood that explains the existence of aging by the allocation of resources from somatic maintenance to reproduction.

DNA damage theory of aging: theory that argues that aging is due to the accumulation of DNA damage with ensuing cellular alterations and disruption of tissue homeostasis.

Dyskeratosis congenita: genetic disease caused by defects in the dyskerin protein, one of the components of telomerase.

Ectotherm: a cold-blooded animal, such as a reptile, fish, or amphibian, whose body temperature is mostly determined by the surrounding environment.

Endocrine system: group of hormone-producing glands and their secretions (hormones); the endocrine system have been implicated in aging.

Endotherm: a warm-blooded animal, like a bird and mammal, capable of regulating its internal temperature.

Epigenetics: study of heritable changes in a phenotype that are not due to alterations in the DNA sequence but rather due to chemical changes of the DNA and associated proteins.

Eutherian: a placental mammal. All mammals are eutherians with the exception of marsupials and monotremes.

Exonuclease: enzyme that cleaves nucleotides from one end of a strand of nucleic acid.

Free radical theory of aging: theory by Denham Harman that argues that aging is a result of damage accumulation caused by reactive oxygen species.

Gene: DNA sequence that encodes a protein and represents the basic unit of inheritance.

Genetics: the study of heredity--i.e., the passing of characteristics from one generation to another--and of variation of inherited characteristics. Aging has a strong genetic component.

Genomics: the study of an organism's genome.

Genome: the full DNA sequence of an organism.

Genotype: genetic makeup of a given organism, usually related to a given characteristic.

Geriatrics: the medical study of diseases and problems of the elderly.

Germ cells: the reproductive cells which contain the genetic material passed on to the offspring.

Gerontology: the scientific study of the aging process and old age. In the context of, gerontology refers to the biological study of aging and old age, also called biogerontology.

Hayflick limit: the inability of cells to replicative indefinitely in culture.

Helicase: an enzyme that unwinds the DNA helix.

IMR: initial mortality rate. The age-independent mortality rate obtained from the Gompertz equation.

Iteroparous: an organism that may reproduce more than once during its lifespan.

Life expectancy: how long, on average, an animal can be expected to live. Can be used interchangeably with average lifespan and average longevity.

Life history: the changes organisms undergo from conception to death, focusing particularly on the schedule of reproduction and survival.

Lifespan: the period of time in which the life events of a species or sub-species (e.g., a strain or population) typically occur. Can sometimes be used interchangeably with longevity even though they have slightly different meanings.

Longevity: the period of time an organism is expected to live under ideal circumstances. Can sometimes be used interchangeably with lifespan even though they have slightly different meanings.

Maximum lifespan (tmax): the maximum period of time organisms of a given species or sub-species (e.g., a strain or population) can live. Usually refers to the longevity of the longest-lived individual of a given species or sub-species.

Mechanical senescence: age-related changes that are a consequence of mechanical usage.

Mitochondrion: cellular organelle that produces most of the cell's energy.

MRDT: mortality rate doubling time. The time required for the mortality rate to double. Inferred from the Gompertz equation.

Mutation: change in the DNA sequence of an organism or cell.

Mutation accumulation theory: theory by Peter Medawar that explains the existence of aging by the accumulation of mutations with harmful effects at later ages.

Negligible senescence: organisms in which the aging process has not been detected in spite of detailed studies, as observed in some animals.

Oocyte: a female gametocyte that develops into an ovum after two meiotic divisions.

Oogenesis: formation of new oocytes.

Oxidative stress: damage caused by reactive oxygen species; oxidative stress has been implicated in aging.

Phenotype: the characteristics of an organism as determined by both genetic makeup and environmental influences.

Phylogeny: the evolutionary development and history of a species or taxonomic group of species.

Polyphenism: the ability of a single genome to give rise to two or more morphologies.

Polyphyodont: an animal that develops several sets of teeth successively throughout its life, as observed in many species.

Polyploid: a cell with three or more sets of chromosomes.

Progeria: genetic disease resembling accelerated aging which typically affects children. Also called Hutchinson-Gilford syndrome.

Progeroid: a phenotype with features resembling accelerated aging.

Quiescent: in cell biology, a quiescent cell is one that is not dividing.

Rate of living theory: theory that argues that lifespan inversely correlates with metabolic rates.

Reactive oxygen species (ROS): any of a number of highly reactive forms of oxygen that are potential sources of damage; damage caused by ROS has been implicated in aging.

Replicative senescence: irreversible cessation of cell division of normally proliferating cells. It is also characterized by various biomarkers and can or not be accompanied by cell death.

Semelparous: organisms that reproduce only once, usually followed by death, as observed in several animals.

Senescence: the fundamental process of aging or aging itself. Can also refer to cellular aging in some contexts.

Senescent cell: normally dividing cell that is irreversibly growth arrested and exhibits a number of other biomarkers associated with cellular senescence.

Soma: the entire body of an organism with exception of the germ cells.

Stem cell: an undifferentiated cell that can divide, differentiate into specialized cells, and can self-renew to give rise to more stem cells.

Strategies for engineered negligible senescence (SENS): a proposal by Aubrey de Grey that details how by reversing seven forms of cellular and molecular age-related changes will allow us to cure aging.

Stress-induced premature senescence (SIPS): irreversible cell cycle arrest and associated cell phenotypes as the result of subcytotoxic stress.

Supercentenarian: someone 110 years of age or older.

Topoisomerase: an enzyme that regulate the supercoiling structure of the DNA.

Taxon (plural: taxa): a taxonomic group of any rank.

Telomeres: the long end sequences of a DNA strand occurring at the tip of the chromosomes that play a key role in replicative senescence.

Telomerase: enzyme that adds telomeric sequences to the telomeres and has been associated with cellular immortality.

Trait: a particular characteristic of an organism that can have different phenotypes.

Werner syndrome (WS): genetic disease resembling accelerated aging; it typically has an adult onset.

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