Age-related changes in organ systems and homeostenosis
Homeostenosis and loss of reserve, then system by system the physiological changes of ageing (cardiovascular, respiratory, renal, body composition, liver, nervous, musculoskeletal, immune and endocrine including menopause and male hormonal decline), with worked numbers for PaO2, creatinine clearance, maximum heart rate and drug distribution, and how each change explains atypical presentations.
Tier 2Medical sciences concept
Written with AI assistance and fact-checked against the sources below. For exam study, not clinical decisions. How notes are made
At a glance
- Ageing changes reserve more than resting function. A fit 85-year-old can have normal resting cardiac output, sodium and glucose, but much less capacity to raise them under stress.
- Homeostenosis describes this narrowing. Each year of life uses up some of the margin between baseline and the threshold for clinical failure, so a smaller insult is needed to cause delirium, falls, heart failure or acute kidney injury.
- Changes vary between organs and between people. Chronological age is a poor guide; frailty and disease explain much of the decline once attributed to ageing.
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Sources
- Brocklehurst's Textbook of Geriatric Medicine and Gerontology (8th ed.)Elsevier (Fillit, Rockwood and Young, 2017), 2017
- Taffet GE. Physiology of aging. In: Hazzard's Geriatric Medicine and Gerontology (8th ed.)McGraw Hill (Halter et al., 2022), 2022
- Sorbini CA et al. Arterial oxygen tension in relation to age in healthy subjects. Respiration 1968;25:3-13Respiration (Karger), 1968
- Mellemgaard K. The alveolar-arterial oxygen difference: its size and components in normal man. Acta Physiol Scand 1966;67:10-20Acta Physiologica Scandinavica, 1966
- Lindeman RD, Tobin J, Shock NW. Longitudinal studies on the rate of decline in renal function with age (Baltimore Longitudinal Study of Aging). J Am Geriatr Soc 1985;33:278-85Journal of the American Geriatrics Society, 1985
- Cruz-Jentoft AJ et al. Sarcopenia: revised European consensus on definition and diagnosis (EWGSOP2). Age Ageing 2019;48:16-31Age and Ageing (Oxford University Press), 2019
- Position statementsAU/NZAustralian and New Zealand Society for Geriatric Medicine, current
- Menopause information for health professionalsAU/NZAustralasian Menopause Society, current
- Last updated
- 14 November 2026
What changed
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