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This chapter addresses the following Geriatric Fellowship Curriculum Milestone: #9


“Besides more or less obvious physical changes in old age, physiological investigation may reveal increasing limitation of the effectiveness of homeostatic devices which keep the bodily conditions stable.”

Walter Bradford Cannon (1871–1945)

Learning Objectives

  • Understand the concepts of homeostasis and homeostenosis.

  • Describe the impact of aging on homeostatic mechanisms which help maintain a normal physiologic body temperature in the face of lowered or increased ambient temperature.

  • Describe the clinical features—including epidemiology, symptoms, signs, results of diagnostic tests and treatment—of both hypothermia and hyperthermia.

  • Describe the impact of aging on the ability to maintain a normal blood pressure in the face of orthostasis, meal ingestion, and hypovolemia.

Key Clinical Points

  1. Homeostasis reflects the aggregate effect of varied mechanisms that maintain normal physiologic constancy in the face of different extrinsic challenges. Aging is associated with impaired homeostasis, or homeostenosis, in the form of diminished capacity to respond to varied challenges.

  2. Aging is associated with a failure of several different homeostatic mechanisms that enhance the risk of hypothermia in the face of decreased ambient temperature.

  3. Aging is associated with a failure of homeostatic mechanisms which enhance the risk of hyperthermia and heatstroke in the face of increased ambient temperature.

  4. The clinical presentation of hypothermia and hyperthermia may be subtle in the older adults, requiring a high index of suspicion and careful supportive management in order to avoid the high rate of mortality associated with these conditions in late life.

  5. Aging is also associated with homeostatic deficits when confronted with the assumption of the upright posture, eating, hypovolemia or a fluid challenge, increased or decreased sodium level, increased or decreased glucose level, bladder filling or bladder outlet obstruction, major burns or trauma, bed rest, or exercise.

  6. Features of homeostatic dysregulation in old age include diminished physiologic reserve, loss of complexity, enhanced variability, normal or enhanced basal activity, excess response to stressors in terms of the sympathetic nervous system, diminished end-organ responsiveness, and loss of negative feedback.

  7. The accumulation of repeated exposure of such challenges resulting in an increased biological burden—termed allostatic load has been shown to be predictive of mortality and frailty including future declines in cognitive and physical function.


Older patients present the clinician with many unique challenges. Many of these are fully discussed in chapters that address the care of older adults in the context of individual organ systems and diseases. However, some of the most complex, common, debilitating, and costly clinical problems seen in geriatrics are extremely challenging precisely because they defy conventional medical wisdom by crossing traditional organ- and discipline-based boundaries. Termed “geriatric syndromes,” conditions such as frailty (Chapter 46), delirium (Chapter 47), falls (Chapter 48), sleep disorders (Chapter 49), dizziness (Chapter 50), syncope (Chapter 51), pressure ulcers (Chapter ...

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