Biogerontologists vary in the degree to which they focus on the study of the aging process as a means of mitigating the diseases of aging or extending lifespan, although most agree that extension of lifespan will necessarily flow from reductions in age-related disease and frailty, although some argue that maximum life span cannot be altered or that it is undesirable to try. Geroscience is a recently formulated interdisciplinary field that embraces biomedical gerontology as the center of preventing diseases of aging through science.
In contrast with biogerontology, which aims to prevent age-related disease by intervening in aging processes, geriatrics is a field of medicine that studies the treatment of existing disease in aging people. There are numerous theories of aging, and no one theory has been accepted. There is a wide spectrum of the types of theories for the causes of aging with programmed theories on one extreme and error theories on the other. Regardless of the theory, a commonality is that as humans age, functions of the body decline.
Stochastic theories of aging are theories suggesting that aging is caused by small changes in the body over time and the body's failure to restore the system and mend the damages to the body.
The cells and tissues are eventually injured due to the damage gathered over time. This causes the diminishes in an organ's function related to age. The notion of accumulated damage was first introduced by Weisman as the "wear and tear" theory.
Wear and tear theories of aging suggest that as an individual ages, body parts such as cells and organs wear out from continued use. Wearing of the body can be attributable to internal or external causes that eventually lead to an accumulation of insults which surpasses the capacity for repair. Due to these internal and external insults, cells lose their ability to regenerate, which ultimately leads to mechanical and chemical exhaustion. Some insults include chemicals in the air, food, or smoke.
Other insults may be things such as viruses, trauma, free radicals, cross-linking, and high body temperature. Accumulation theories of aging suggest that aging is bodily decline that results from an accumulation of elements, whether introduced to the body from the environment or resulting from cell metabolism. Free radicals are reactive molecules produced by cellular and environmental processes, and can damage the elements of the cell such as the cell membrane and DNA and cause irreversible damage.
The free-radical theory of aging proposes that this damage cumulatively degrades the biological function of cells and impacts the process of aging. These conditions become more common as humans grow older and include diseases related to aging, such as dementia, cancer and heart disease.
DNA damage has been one of the many causes in diseases related to aging. The stability of the genome is defined by the cells machinery of repair, damage tolerance, and checkpoint pathways that counteracts DNA damage.
One hypothesis proposed by Gioacchino Failla in  is that damage accumulation to the DNA causes aging. The cross-linking theory proposes that advanced glycation end-products stable bonds formed by the binding of glucose to proteins and other aberrant cross-links accumulating in aging tissues is the cause of aging.
The crosslinking of proteins disables their biological functions. The hardening of the connective tissue, kidney diseases, and enlargement of the heart are connected to the cross-linking of proteins. Crosslinking of DNA can induce replication errors, and this leads to deformed cells and increases the risk of cancer.
Genetic theories of aging propose that aging is programmed within each individual's genes. According to this theory, genes dictate cellular longevity. Programmed cell death, or apoptosis , is determined by a "biological clock" via genetic information in the nucleus of the cell.
Genes responsible for apoptosis provide an explanation for cell death, but are less applicable to death of an entire organism.
- Annual Review of Gerontology and Geriatrics, Volume 31, 2011.
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An increase in cellular apoptosis may correlate to aging, but is not a 'cause of death'. Environmental factors and genetic mutations can influence gene expression and accelerate aging.
More recently epigenetics have been explored as a contributing factor. The epigenetic clock , which objectively measures the biological age of cells and tissues, may become useful for testing different biological aging theories. General imbalance theories of aging suggest that body systems, such as the endocrine , nervous , and immune systems, gradually decline and ultimately fail to function. The rate of failure varies system by system. The immunological theory of aging suggests that the immune system weakens as an organism ages. This makes the organism unable to fight infections and less able to destroy old and neoplastic cells.
This leads to aging and will eventually lead to death. This theory of aging was developed by Ray Walford, an American gerontologist. According to Walford, incorrect immunological procedures are the cause of the process of aging. Social gerontology is a multi-disciplinary sub-field that specializes in studying or working with older adults. Social gerontologists may have degrees or training in social work , nursing , psychology , sociology , demography , public health , or other social science disciplines.
Social gerontologists are responsible for educating, researching, and advancing the broader causes of older people.
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Because issues of life span and life extension need numbers to quantify them, there is an overlap with demography. Those who study the demography of the human life span differ from those who study the social demographics of aging. Several theories of aging are developed to observe the aging process of older adults in society as well as how these processes are interpreted by men and women as they age.
Activity theory was developed and elaborated by Cavan, Havighurst, and Albrecht. According to this theory, older adults' self-concept depends on social interactions.
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In order for older adults to maintain morale in old age, substitutions must be made for lost roles. Examples of lost roles include retirement from a job or loss of a spouse. Activity is preferable to inactivity because it facilitates well-being on multiple levels. Because of improved general health and prosperity in the older population, remaining active is more feasible now than when this theory was first proposed by Havighurst nearly six decades ago.
The activity theory is applicable for a stable, post-industrial society , which offers its older members many opportunities for meaningful participation. Weakness: Some aging persons cannot maintain a middle-aged lifestyle, due to functional limitations, lack of income, or lack of a desire to do so. Many older adults lack the resources to maintain active roles in society. On the flip side, some elders may insist on continuing activities in late life that pose a danger to themselves and others, such as driving at night with low visual acuity or doing maintenance work to the house while climbing with severely arthritic knees.
In doing so, they are denying their limitations and engaging in unsafe behaviors. Disengagement theory was developed by Cumming and Henry. According to this theory, older adults and society engage in a mutual separation from each other. An example of mutual separation is retirement from the workforce. A key assumption of this theory is that older adults lose "ego-energy" and become increasingly self-absorbed.
Additionally, disengagement leads to higher morale maintenance than if older adults try to maintain social involvement. This theory is heavily criticized for having an escape clause - namely, that older adults who remain engaged in society are unsuccessful adjusters to old age. Gradual withdrawal from society and relationships preserves social equilibrium and promotes self-reflection for elders who are freed from societal roles.
It furnishes an orderly means for the transfer of knowledge, capital, and power from the older generation to the young. It makes it possible for society to continue functioning after valuable older members die.
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Continuity theory is an elusive concept. On one hand, to exhibit continuity can mean to remain the same, to be uniform, homogeneous, unchanging, even humdrum. This static view of continuity is not very applicable to human aging. On the other hand, a dynamic view of continuity starts with the idea of a basic structure which persists over time, but it allows for a variety of changes to occur within the context provided by the basic structure.
The basic structure is coherent: It has an orderly or logical relation of parts that is recognizably unique and that allows us to differentiate that structure from others. With the introduction of the concept of time, ideas such as direction, sequence, character development, and story line enter into the concept of continuity as it is applied to the evolution of a human being. In this theory, a dynamic concept of continuity is developed and applied to the issue of adaptation to normal aging.
A central premise of continuity theory is that, in making adaptive choices, middle-aged and older adults attempt to preserve and maintain existing internal and external structures and that they prefer to accomplish this objective by using continuity i. In middle and later life, adults are drawn by the weight of past experience to use continuity as a primary adaptive strategy for dealing with changes associated with normal aging. To the extent that change builds upon, and has links to, the person's past, change is a part of continuity. As a result of both their own perceptions and pressures from the social environment, individuals who are adapting to normal aging are both predisposed and motivated toward inner psychological continuity as well as outward continuity of social behavior and circumstances.
Continuity theory views both internal and external continuity as robust adaptive strategies that are supported by both individual preference and social sanctions.
Continuity theory consists of general adaptive principles that people who are normally aging could be expected to follow, explanations of how these principles work, and a specification of general areas of life in which these principles could be expected to apply. Now, more than ever before, researchers require conceptually explicit instruments designed to assess individual and social behaviors, attitudes, and traits in the elderly population.
This is the first in a three-volume series designed to serve the needs of researchers, evaluators, and clinicians in assessing the instruments used in the field of aging. The measures review in Volume 1 focus on the cognitive reactions of older people to aging and on the assessments of aging made by people who are not yet old. This volume also contains the series introduction which explains the methods used for evaluating the instruments and assesses the status of gerontological measurement today. Each chapter is devoted to instruments in a particular subject area such as intellectual functioning, personality, self-esteem, and ethnic group identification.
Most chapters are composed of three parts. First, there is a concise narrative review of the major theoretical concerns and measurement strategies within that particular research domain. The second part is a collection of abstracts, each of which presents a conceptual definition and a description of a specific instrument together with data about samples, reliability, validity, scaling properties, and correlations with age. Whenever possible the instruments themselves constitute the third part of the chapter.
Perceptual and Motor Skills 1, International Psychogeriatrics 2: , Yesavage JA: The use of self-rating depression scales in the elderly. Clinical Gerontologist 3: , Yesavage JA: Problems in the care of neuropsychiatric disorders in the aged. Proceedings of the 17th International Congress of Internal Medicine : , Psychosocial Issues.
Yesavage JA: Senile dementia treatments.
Related Annual Review of Gerontology and Geriatrics, Volume 3, 1982: Clinical, Behavioral and Social Issues
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