Mohammed T. Abou-Saleh

Principles and Practice of Geriatric Psychiatry.Editors: Professor John R. M. Copeland, Dr Mohammed T. Abou-Saleh and Professor Dan G. BlazerCopyright & 2002 John Wiley & Sons LtdPrint ISBN 0-471-98197-4 Online ISBN 0-470-84641-05General Theories of AgingEwald W. BusseDuke University Medical Center, Durham, NC, USAINTRODUCTIONThere is no satisfactory composite theory of aging, butnumerous theories have been advanced to explain how andwhy living organisms age and die 1,2 . Given the multidimensionalityof human beings, many theories of aging, some familiarand some overlapping, have been developed. Theories of agingare usually grouped by biological, psychological, or sociologicalsciences. A comprehensive review of theories of aging is beyondthe scope of this chapter. However, the selected theories thatare to be reviewed are particularly relevant to the psychiatry ofold age.Depending on the discipline, the phenomenon of aging takes ondifferent definitions. Biologic aging is made up of a number ofundesirable processes. There are multiple processes of aging thatresult in a decline in efficiency of the organism and end in itsdeath. Aging, particularly in the psychosocial sciences, oftenincludes a desirable process of maturation, that is, acquiring adesirable quality such as wisdom.hypothalamus, appear to be much more vulnerable than others.In aging, not only are neurons lost, but there are alterations ofneuronal synapses and networks 6 .Apoptosis is a ‘‘physiological normal process by which multicellularorganisms get rid of injured, infected or developmentallyunnecessary cells’’ 7,8 . Apoptosis is similar, if not identical,to a programmed cell death. The term is derived from Greekand means the dropping of petals from flowers or leaves fromtrees. The term ‘‘necrosis’’ is also commonly used to describeanother kind of cell death. Necrosis is a type of cell death thatis the result of the failure of nutrients to reach the cell. Deathby necrosis is quite different from death by apoptosis. Innecrosis the cells blow up, spill their contents and start animmune response. In apoptosis, however, the cells seem tocondense, but develop blebs that separate and form ‘‘apoptosisbodies’’. Apoptosis bodies undergo rapid phagocytosis; thus, inapoptosis the cells die with little observable reaction, whilewhen they die of necrosis they produce a widespread inflammatoryresponse.THE BIOLOGICAL THEORIES OF AGINGBiological theories of aging can be broken down into two broadcategories: the developmental genetic theories (primary aging) andthe stochastic theories (secondary aging processes) 3,4 . Primaryaging refers to those declines in function that are geneticallycontrolled, while secondary (stochastic) aging consists of randomchanges resulting from acquired disease and trauma. If the hostileevents related to secondary aging could be prevented, life wouldbe extended but, because of primary aging, decline and death areinevitable.Deliberate Biological ProgrammingHayflick and Moorhead 5 made an important contribution to ourunderstanding of cellular aging. They demonstrated that humanmitotic cells would divide a finite number of times and then thecell culture would die. Numerous studies demonstrated that the‘‘normal’’ cells have a memory for the number of duplications,which is believed to be encoded in the genetic material. Incontrast, cancer cells have abnormal chromosomes and have thecapacity for dividing endlessly.The capacity for a programmed cell death that exists in mitotic(dividing) cells is also present in postmitotic (non-dividing) cells.Cells incapable of dividing, such as neurons, do age and die.Certain types of brain cells, such as those located in theGenetics of Human AgingIn humans and in many other animal species, females outlivemales and this difference can be attributed to genetic factors, asthe male has a Y and an X chromosome and the female has two Xchromosomes. The small Y chromosome does not appear tocontain sufficient genetic material for the normal development orwell-being of a human. Its primary function is to provide malecharacteristics 9 . Chromosomes contain the vast majority of genes,but a few exist within the mitochondria. Mitochondrial genes areimportant to aerobic respiration and age changes. All mitochondrialgenes are inherited from the mother 10 .The Aging ClockMiller provides a working definition of aging as follows: ‘‘Aging isa process that converts fit adults into frail adults with aprogressive increased risk of illness, injury and death’’ 11 . Hefavors as an explanation for aging the existence of a single agingclock. This aging clock is in turn linked to many of the observedbiological clocks that are seen in both humans and animals. Millerholds that a useful way of determining biological age willeventually emerge rather than depending upon chronologicalage. He supports the view that the genetic control of lifespanshould be considered relatively minor. He believes that itinfluences lifespan at no more than 15–35%. Living in a favorablePrinciples and Practice of Geriatric Psychiatry, 2nd edn. Edited by J. R. M. Copeland, M. T. Abou-Saleh and D. G. Blazer&2002 John Wiley & Sons, Ltd