Clinical meaning
Aging is a universal, progressive, and irreversible biological process characterized by the gradual decline of physiological function across all organ systems. At the cellular level, aging involves the accumulation of oxidative damage to DNA, proteins, and lipids from reactive oxygen species (free radicals); progressive telomere shortening with each cell division (the Hayflick limit, after which cells enter senescence); decreased mitochondrial efficiency (reducing cellular energy production); accumulation of lipofuscin (a wear-and-tear pigment) in postmitotic cells such as neurons and cardiac myocytes; and decreased capacity for cellular repair and regeneration. These cellular changes manifest as organ-specific functional decline that the practical nurse must understand to distinguish normal aging from pathological conditions. In the cardiovascular system, the myocardium thickens (left ventricular hypertrophy), the aorta and large arteries stiffen (arteriosclerosis, not atherosclerosis), systolic blood pressure tends to increase (isolated systolic hypertension), cardiac output decreases at rest by approximately 1% per year after age 30, and the conduction system degenerates (increased risk of dysrhythmias, especially atrial fibrillation). In the respiratory system, chest wall compliance decreases due to calcification of costal cartilage, the diaphragm weakens, residual...