Selected Physiologic Age-Related Changes
Affected Organ or System | Physiologic Change | Clinical Manifestations |
|---|---|---|
Body composition | ↓ Lean body mass ↓ Muscle mass ↓ Creatinine production ↓ Skeletal mass ↓ Total body water ↑ Percentage adipose tissue (until age 60, then ↓ until death) | Changes in medication levels (usually ↑) ↓ Strength Susceptibility to dehydration |
Cells | ↑ DNA damage and ↓DNA repair capacity ↓ Oxidative capacity Accelerated cell senescence ↑ Fibrosis Lipofuscin accumulation | ↑ Cancer risk |
CNS | ↓ Number of dopamine receptors ↑ Alpha-adrenergic responses ↑ Muscarinic parasympathetic responses | Tendency toward stiffer muscles, less flexibility, impaired balance, and loss of spontaneous movements (eg, ↑ muscle tone, ↓ arm swing) |
Ears | Loss of high-frequency hearing | ↓ Ability to recognize speech |
Endocrine system | ↑ Insulin resistance and glucose intolerance | ↑ Incidence of diabetes |
Menopause, ↓ estrogen and progesterone secretion ↓ Testosterone secretion ↓ Growth hormone secretion ↓Vitamin D absorption and activation ↑ Incidence of thyroid abnormalities ↑ Bone mineral loss ↑ Secretion of ADH in response to osmolar stimuli | Vaginal dryness, dyspareunia ↓ Muscle mass ↓Bone mass ↑ Fracture risk Changes in skin Susceptibility to water intoxication | |
Eyes | ↓ Lens flexibility ↑ Time for pupillary reflexes (constriction, dilation) ↑ Incidence of cataracts | Presbyopia ↑ Glare and difficulty adjusting to changes in lighting ↓ Visual acuity |
GI tract | ↓ Splanchnic blood flow ↑ Transit time | Susceptibility to constipation and diarrhea |
Heart | ↓ Intrinsic heart rate and maximal heart rate Blunted baroreflex (less increase in heart rate in response to decrease in BP) ↓ Diastolic relaxation ↑ Atrioventricular conduction time ↑ Atrial and ventricular ectopy | Susceptibility to syncope ↓ Ejection fraction ↑ Rates of atrial fibrillation ↑ Rates of diastolic dysfunction and heart failure with reduced ejection fraction |
Immune system | ↓ T-cell function ↓ B-cell function | ↑ Susceptibility to infections and possibly cancer ↓ Antibody response to immunization or infection but ↑ autoantibodies |
Joints | Degeneration of cartilaginous tissues Fibrosis ↑ Glycosylation and cross-linking of collagen Loss of tissue elasticity | Tightening of joints Susceptibility to osteoarthritis |
Kidneys | ↓ Renal blood flow ↓ Renal mass ↓ Glomerular filtration ↓ Renal tubular secretion and reabsorption ↓ Ability to excrete a free-water load | Changes in medication levels with ↑ risk of adverse drug effects Susceptibility to nocturia, if free water taken shortly before sleep |
Liver | ↓ Hepatic mass ↓ Hepatic blood flow ↓ Activity of CYP450 enzyme system | Changes in medication levels |
Nose | ↓ Smell ↑ Mucosal thinning or capillary fragility | ↓ Taste and consequent ↓ appetite ↑ Likelihood (slightly) of nosebleeds |
Peripheral nervous system | ↓ Baroreflex responses (less increase in heart rate in response to decrease in BP) ↓ Beta-adrenergic responsiveness and number of receptors ↓ Signal transduction ↓ Muscarinic parasympathetic responses Preserved alpha-adrenergic responses | Susceptibility to syncope ↓ Response to beta-blockers Exaggerated response to anticholinergic medications |
Pulmonary system | ↓ Vital capacity ↓ Lung elasticity (compliance) ↑ Residual volume ↓ FEV1 ↑ V/Q mismatch | ↑ Likelihood of shortness of breath during vigorous exercise if people are normally sedentary or if exercise is performed at high altitudes ↑ Risk of death due to pneumonia ↑ Risk of serious complications (eg, respiratory failure) for patients with a pulmonary disorder |
Vasculature | ↓ Endothelin-dependent vasodilation ↑ Peripheral resistance | Susceptibility to hypertension |
↓ = decreased; ↑ = increased; FEV1= forced expiratory volume in 1 sec; V/Q = ventilation/perfusion. | ||
Adapted from the Institute of Medicine: Pharmacokinetics and Drug Interactions in the Elderly Workshop. Washington DC, National Academy Press, 1997, pp. 8–9. | ||
