Physiology of Aging

With aging, there is an apparent depletion of physiologic reserves that has been termed homeostenosis. When the reserves are depleted, the older adult is intolerant of further challenges without crossing a precipice, that is, frailty. However, in the absence of a challenge, many of the age-related changes are not clinically apparent. The reserves are, in part, in use just to maintain homeostasis, and studies that measure how much they are in use, allostatic load, can predict age-associated outcomes. Inflammation at low levels and associated with age may be a driver of many of these processes. Because aging is experienced in diverse fashion, the heterogeneity of older adults is great and the differences between the aging of men and women are being increasingly recognized. Similarly, the heterogeneity in the loss of reserves among older adults contributes to their nonspecific presentations on illness. Understanding the fundamental age-related changes allows us to appreciate the unique population that older adults create.