HUMAN AGING

physiological changes that take place in the human body leading to senescence, the decline of biological functions and of the ability to adapt to metabolic stress. In humans the physiological developments are normally accompanied by psychological and behavioural changes, and other changes, involving social and economic factors, also occur. Aging begins as soon as adulthood is reached and is as much a part of human life as are infancy, childhood, and adolescence. Gerontology (the study of aging) is concerned primarily with the changes that occur between the attainment of maturity and the death of the individual. The goal of research in gerontology is to identify the factors that influence these changes. Application of this knowledge is expected to reduce the disabilities now associated with aging. The biological-physiological aspects of aging include both the basic biological factors that underlie aging and the general health status. Since the probability of death increases rapidly with advancing age, it is clear that changes must occur in the individual which make him more and more vulnerable to disease. For example, a young adult may rapidly recover from pneumonia, whereas an elderly person may die. Physiologists have found that the performance of many organs such as the heart, kidneys, brain, or lungs shows a gradual decline over the life span. Part of this decline is due to a loss of cells from these organs, with resultant reduction in the reserve capacities of the individual. Furthermore, the cells remaining in the elderly individual may not perform as well as those in the young. Certain cellular enzymes may be less active, and thus more time may be required to carry out chemical reactions. Ultimately the cell may die. Additional reading George L. Maddox et al. (eds.), The Encyclopedia of Aging, 2nd ed. (1995), is an extensive general reference. General principles are addressed in Paola S. Timiras (ed.), Physiological Basis of Aging and Geriatrics, 2nd ed. (1994), addressing the aging process from a physiological viewpoint including all systems of the body; Imre Zs.-Nagy, The Membrane Hypothesis of Aging (1994), a comprehensive, multidisciplinary description of the cell maturation and aging process; Arthur K. Labin (ed.), Practical Handbook of Human Biologic Age Determination (1994), covering metabolic profiles, organ system approaches, biological measurements, and nonhuman model studies; Robert Arking, Biology of Aging: Observations and Principles (1991); and Alexander P. Spence, Biology of Human Aging (1989).The following provide advanced knowledge on various aspects of geriatrics and gerontology: Jean M. Lauder et al. (eds.), Molecular Aspects of Development and Aging of the Nervous System (1989); Claire Murphy, William S. Cain, and D. Mark Hegsted (eds.), Nutrition and the Chemical Senses in Aging: Recent Advances and Current Research Needs (1989); Allan L. Goldstein (ed.), Biomedical Advances in Aging (1990); and Steven R. Gambert (ed.), Handbook of Geriatrics (1987). The essentials of geriatric medicine are presented in William Reichel, Care of the Elderly: Clinical Aspects of Aging, 4th ed. (1995), a comprehensive clinical approach geared to the practicing physician; M.R.P. Hall, W.J. MacLennan, and M.D.W. Lye, Medical Care of the Elderly, 3rd ed. (1993); and Contemporary Geriatric Medicine (biennial).Alan J. Sinclair and Ken W. Woodhouse (eds.), Acute Medical Illness in Old Age (1995) , presents guidelines for effectively managing various conditions in the elderly. Richard L. Byyny and Leon Speroff, A Clinical Guide for the Care of Older Women: Primary and Preventive Care, 2nd ed. (1996), addresses issues of older female patients such as specific guidelines for screening, diagnosis, and management. Cornelius L.E. Katona, Depression in Old Age (1994), covers clinical features, measurement, etiology, and other aspects of aging. Margret M. Baltes and Paul B. Baltes (eds.), The Psychology of Control and Aging (1986), focuses on control-related beliefs and behaviours with regard to theory and practice in the psychology of aging. Gerald Felsenthal, Susan J. Garrison, and Franz U. Steinberg (ed.), Rehabilitation of the Aging and Elderly Patient (1994), focuses on practices to prevent or delay confinement of patients to custodial institutions and on the rehabilitation of both disabled and elderly patients who are losing functions.