Chapter 62: The Physiology of Aging

Aging involves progressive deterioration of cellular and organ function, driven by accumulation of molecular damage, telomere shortening, mitochondrial dysfunction, and impaired protein synthesis and degradation pathways. The aging process affects multiple physiological systems simultaneously: cardiovascular function declines through reduced myocardial contractility, increased arterial stiffness, and compromised baroreceptor sensitivity; respiratory capacity diminishes due to loss of elastic recoil in lung tissue and weakened respiratory muscles; nervous system changes include reduced synaptic plasticity, delayed neural transmission, and cognitive decline related to neurodegeneration; endocrine function deteriorates with altered hormone secretion patterns and reduced tissue responsiveness to hormonal signals; and immune function becomes impaired through thymic involution and reduced lymphocyte production, increasing susceptibility to infection and autoimmune dysfunction. Skeletal muscle undergoes sarcopenia, characterized by progressive fiber loss and reduced contractile protein content, leading to decreased strength and mobility. Bone density declines through imbalanced osteoblast and osteoclast activity, increasing fracture risk. Renal function diminishes with reduced glomerular filtration rate and impaired tubular reabsorption, affecting fluid and electrolyte balance. Thermoregulation becomes less efficient, increasing vulnerability to temperature extremes. Metabolic rate decreases while body composition shifts toward increased adiposity and reduced lean mass. The chapter integrates discussion of cellular senescence, oxidative stress accumulation, and genetic factors influencing longevity. Understanding these age-related physiological changes provides foundation for clinical management of elderly patients and strategies for maintaining functional capacity during aging.