Physical Changes With Aging: Approach to the Geriatric Patient: Merck Manual Professional

Selected Physiologic Age-Related Changes
Affected Organ or System	Physiologic Change	Clinical Manifestations
Body composition	↓ Lean body mass ↓ Muscular mass ↓ Creatinine production ↓ Skeletal mass ↓ Total body water ↑ Percentage adipose tissue (until age 60, then ↓until death)	Changes in drug levels ↓ Strength Tendency toward dehydration
Cells	↑ DNA damage and ↓DNA repair capacity ↓ Oxidative capacity Accelerated cell senescence ↑ Fibrosis Lipofuscin accumulation	↑ Cancer risk
CNS	↓ Number of dopamine receptors ↑ α-Adrenergic responses ↑ Muscarinic parasympathetic responses	Tendency toward parkinsonian symptoms (eg, ↑ muscle tone, ↓ arm swing)
Ears	Loss of high-frequency hearing	↓ Ability to recognize speech
Endocrine system	Menopause, ↓ estrogen and progesterone secretion ↓ Testosterone secretion ↓ Growth hormone secretion ↓ Vitamin D absorption and activation ↑ Incidence of thyroid abnormalities ↑ Incidence of diabetes (↓ insulin sensitivity or ↑ insulin resistance) ↑ Bone mineral loss ↑ Secretion of ADH in response to osmolar stimuli	↓ Muscle mass ↓Bone mass ↑ Fracture risk Vaginal dryness Changes in skin Tendency toward 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	Tendency toward 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	Tendency toward syncope ↓ Ejection fraction
Immune system	↓ T-cell function ↓ B-cell function	Tendency toward some infections and possibly cancer ↓ Antibody response to immunization or infection but ↑ autoantibodies
Joints	Degeneration of cartilaginous tissues Fibrosis ↓ Elasticity	Tightening of joints Tendency toward osteoarthritis
Kidneys	↓ Renal blood flow ↓ Renal mass ↓ Glomerular filtration ↓ Renal tubular secretion and reabsorption ↓ Ability to excrete a free-water load	Changes in drug levels with ↑ risk of adverse drug effects Tendency toward dehydration
Liver	↓ Hepatic mass ↓ Hepatic blood flow ↓ Activity of P-450 enzyme system	Changes in drug levels
Nose	↓ Smell	↓ Taste and consequent ↓ appetite ↑ Likelihood (slightly) of nosebleeds
Peripheral nervous system	↓ Baroreflex responses ↓ β-Adrenergic responsiveness and number of receptors ↓ Signal transduction ↓ Muscarinic parasympathetic responses Preserved α-adrenergic responses	Tendency toward syncope ↓ Response to β-blockers Exaggerated response to anticholinergic drugs
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 done at high altitudes ↑ Risk of death due to pneumonia ↑ Risk of serious complications for patients with a pulmonary disorder
Vasculature	↓ Endothelin-dependent vasodilation ↑ Peripheral resistance	Tendency toward 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.

Selected Physiologic Age-Related Changes

Affected Organ or System

Physiologic Change

Clinical Manifestations

Body composition	↓ Lean body mass ↓ Muscular mass ↓ Creatinine production ↓ Skeletal mass ↓ Total body water ↑ Percentage adipose tissue (until age 60, then ↓until death)	Changes in drug levels ↓ Strength Tendency toward dehydration
Cells	↑ DNA damage and ↓DNA repair capacity ↓ Oxidative capacity Accelerated cell senescence ↑ Fibrosis Lipofuscin accumulation	↑ Cancer risk
CNS	↓ Number of dopamine receptors ↑ α-Adrenergic responses ↑ Muscarinic parasympathetic responses	Tendency toward parkinsonian symptoms (eg, ↑ muscle tone, ↓ arm swing)
Ears	Loss of high-frequency hearing	↓ Ability to recognize speech
Endocrine system	Menopause, ↓ estrogen and progesterone secretion ↓ Testosterone secretion ↓ Growth hormone secretion ↓ Vitamin D absorption and activation ↑ Incidence of thyroid abnormalities ↑ Incidence of diabetes (↓ insulin sensitivity or ↑ insulin resistance) ↑ Bone mineral loss ↑ Secretion of ADH in response to osmolar stimuli	↓ Muscle mass ↓Bone mass ↑ Fracture risk Vaginal dryness Changes in skin Tendency toward 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	Tendency toward 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	Tendency toward syncope ↓ Ejection fraction
Immune system	↓ T-cell function ↓ B-cell function	Tendency toward some infections and possibly cancer ↓ Antibody response to immunization or infection but ↑ autoantibodies
Joints	Degeneration of cartilaginous tissues Fibrosis ↓ Elasticity	Tightening of joints Tendency toward osteoarthritis
Kidneys	↓ Renal blood flow ↓ Renal mass ↓ Glomerular filtration ↓ Renal tubular secretion and reabsorption ↓ Ability to excrete a free-water load	Changes in drug levels with ↑ risk of adverse drug effects Tendency toward dehydration
Liver	↓ Hepatic mass ↓ Hepatic blood flow ↓ Activity of P-450 enzyme system	Changes in drug levels
Nose	↓ Smell	↓ Taste and consequent ↓ appetite ↑ Likelihood (slightly) of nosebleeds
Peripheral nervous system	↓ Baroreflex responses ↓ β-Adrenergic responsiveness and number of receptors ↓ Signal transduction ↓ Muscarinic parasympathetic responses Preserved α-adrenergic responses	Tendency toward syncope ↓ Response to β-blockers Exaggerated response to anticholinergic drugs
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 done at high altitudes ↑ Risk of death due to pneumonia ↑ Risk of serious complications for patients with a pulmonary disorder
Vasculature	↓ Endothelin-dependent vasodilation ↑ Peripheral resistance	Tendency toward 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.