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Book Review |
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Physiological Basis of Aging and
Geriatrics Fourth edition. Edited by Paola S. Timiras. New York, Informa Healthcare, 2007. 407 pp., illus., index $229.95. ISBN 978-0-8493-7305-3. The expected length of the human life span increased dramatically in industrialized countries during the 20th century. In the United States in 1900, life expectancy at birth was about 48 years while in the early 21st century life expectancy is nearing 80 years. Even in developing countries, life expectancy, though not as high as in the industrialized countries, is increasing. Clearly, humans are aging more successfully than in the past. During much of the last century, the study of aging was devoted to defining the biochemical and physiological changes that occurred in individuals as they aged. In particular, emphasis was on declines in physiological functions that appeared to lead to diseases and disabilities. In more recent years, however, ideas about aging have changed. Research is showing that older adults retain reasonable levels of physiological adaptability and regenerative capability that provide for adequate biological functioning and for increasing lengths of time. The Fourth Edition of Physiological Basis of Aging and Geriatrics, edited by Paola S. Timiras, is certainly timely. It not only maintains the respected tradition of its predecessor editions but also extends that tradition to a recognition of the plasticity of physiological function in the aged. Its 25 chapters are grouped into three parts: Part 1, General Perspectives; Part II, Systemic and Organismic Aging; and Part III, Prevention and Rehabilitation. Throughout, the emphasis is on physiology combined with a liberal coverage of biochemistry and molecular biology. Part I describes demographic, epidemiologic and comparative aspects of aging. Extensive research affirms that individuals experience aging in highly variable ways and show a wide variety of responses to it. Even for individuals of the same age, changes that occur do not involve all the same physiological functions nor do they occur to the same degree or even at the same time. Research has elucidated many of the physiological changes that occur with aging and hinted at the biological basis for at least some of them. We now better understand that functional changes that do occur with aging follow from numerous and complex interactions at diverse genetic and environmental levels. Part I also covers current thinking about theories of aging and evaluates the evidence for each of them. Discussed are the evolutionary basis of aging and the potential roles of gene regulation, error catastrophe, free radical accumulation, programmed cell death, and altered neuroendocrine and immunologic controls. Also considered are insights gained from studies on “comparative aging.” This area considers the fact that species differ widely in longevity. Even so, relevant research has uncovered evidence for conserved metabolic pathways that appear to regulate longevity regardless of its length. Quite recent studies indicate that such conserved pathways involve insulin/IGF-1 and /or GH/IGF-1 in the very short-lived nematodes and flies; the comparatively longer-lived mice and possibly even in the much-longer lived humans. Part II comprises the largest portion of the book and considers the vast amount of information that is accumulating on organ systems and how they age. It thoroughly covers current insights on how the body, as it ages, adjusts its physiology as it works to sustain optimal functioning and to respond to environmental changes. Any new text on aging, to be up-to-date, must accommodate an ever-increasing number of topics. This new text succeeds at doing this in a concise, thorough and authoritative way. Body systems and organs are each discussed in terms of the structural and functional changes that occur or are likely to occur with age. However, it is also clearly shown that some organs such as the pituitary and the parathyroid glands hardly change at all with age. Further, there are only minor changes in renal function with aging. An acute form of renal failure does occur more often in the aged than in younger individuals. Even here, though, considerable progress has been made as mortality from renal failure has significantly decreased during the later years of the twentieth century. A new view about aging of the nervous system has come into vogue. The prior view was that the nervous system severely and progressively deteriorated with age. This view was reinforced by the common observation of detrimental changes in sensory systems such as vision and hearing. In contrast, the current view is that the nervous system is quite plastic and retains the capacity to repair damage and injury into old age. Research shows that normal brain function can persist even in the very elderly. Degenerative disease involving the cardiovascular system remains the single most important cause of death worldwide in both sexes. As people live longer, they become more susceptible to cardiovascular morbidity and ultimately mortality. Nevertheless, progress has been made in our understanding and clinical control of cardiovascular disease. Over the last 50 years, total death rates due to heart disease and stroke, in the more advanced countries at least, have declined 56% and 70%, respectively. Though much study remains to be done to further understand the body’s systems and organs, research is showing that their aging need not be as detrimental as once thought. The body retains its ability to maintain homeostasis and to respond to stress, as long as the stress is not overly severe or prolonged. For the immune system, senescence does not necessarily mean deterioration. In the elderly, innate immunity remains relatively intact. However, acquired immunity is affected and the body’s capacity to cope with a major immunological stress such as a chronic or acute infection does appear to decrease. Even so, basal levels of immune function are maintained with age. Much more interesting and up-to-date information about the aging of body systems and organs is included in Part II. In all cases, current basic and clinical aspects are covered along with updated tables and figures that emphasize current trends and new research data. Part III considers interventions, pharmacologic, nutritional, regenerative and assistive, that further successful aging. For example, research on physical activity and its relation to physiologic aging is very active currently. Indeed, losses once thought inevitable with age, for example loss of muscle mass and strength, can be reduced or even counteracted through regular exercise. Pharmacological medications have obvious benefits. However, they must be used cautiously because, in general, with age, the risk of side effects such as drug-drug interaction, increases. Part III presents useful information on nutrition and diet for the elderly. Included also is the topic of caloric restriction, the use of which was first shown in the 1930s to extend the lifespan of rats. The experimental approach to caloric restriction has been standardized and its use prolongs physiological functional competence, postpones age-related pathologies, and extends the mean and maximum lifespan of multiple species including mammals. In the late 19th century, the theory developed that normal somatic cells are mortal with a finite capacity for replication. This theory was challenged in the first half of the 20th century but finally was vindicated in 1965. Part III discusses the recent finding that a progressive shortening of telomeres in somatic cells, other than germ cells and neoplastic cells, occurs and eventually leads to their inability to replicate. This shortening is due to the shut-down of telomerase, the enzyme that regenerates telomeres to an optimal length. A question currently being researched actively is can telomerase be kept active, with drugs for example, and, if so, will this prolong the life of tissues by keeping their complement of fully functional cells at an optimal level? A related, but very new, area of research discussed in Part III is the use of embryonic stem cells to regenerate aging tissues. In sum, the chapters in this book are up-to-date and very informative. Each chapter is written by one or more experts and is clearly presented and well-illustrated. Each contains useful summary statements and an extensive reference list. An appealing feature of the book is that clinical issues are interspersed throughout. Overall, this is an informative and practical guide on aging for the gerontologist, the geriatrician and the interested layperson who has some background knowledge of biological, especially physiological, concepts. Dennis E. Buetow Univ. of Illinois, Urbana-Champaign |
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