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TABLE A2–1: Physiologic Changes with Aging
Organ System Manifestation
Balance and gait

↓ Stride length and slower gait

↓ Arm swing

↑ Body sway when standing

Body composition

↓ Total body water

↓ Lean body mass

↑ Body fat

↔ or ↓ Serum albumin

↑ α1-Acid glycoprotein (↔ or ↑ by several disease states)


↓ Cardiovascular response to stress

↓ Baroreceptor activity leading to ↑ orthostatic hypotension

↓ Cardiac output

↑ Systemic vascular resistance with loss of arterial elasticity and dysfunction of systems maintaining vascular tone

↓ Resting and maximal heart rate

Central nervous system

↓ Size of the hippocampus and frontal and temporal lobes

↓ Number of receptors of all types and ↑ sensitivity of remaining receptors

↓ Short-term memory, coding and retrieval, and executive function

Altered sleep patterns


↓ Estrogen, testosterone, TSH, and DHEA-S levels

Altered insulin signaling


↓ Motility of the large intestine

↓ Vitamin absorption by active transport mechanisms

↓ Splanchnic blood flow

↓ Bowel surface area


Atrophy of the vagina with decreased estrogen

Prostatic hypertrophy with androgenic hormonal changes

Detrusor hyperactivity may predispose to incontinence


↓ Hepatic size

↓ Hepatic blood flow

↓ Phase I (oxidation, reduction, hydrolysis) metabolism


↓ Antibody production in response to antigen

↑ Autoimmunity


Altered dentition

↓ Ability to taste salt, bitter, sweet, and sour


↓ Respiratory muscle strength

↓ Chest wall compliance

↓ Arterial oxygenation and impaired carbon dioxide elimination

↓ Vital capacity

↓ Maximal breathing capacity

↑ Residual volume



↓ Renal blood flow

↓ Filtration fraction

↓ Tubular secretory function

↓ Renal mass


Presbyopia (diminished ability to focus on near objects)

↓ Night vision

Presbycusis (high-pitch, high-frequency hearing loss)

↓ Sensation of smell and taste


↓ Skeletal bone mass (osteopenia)

Joint stiffening caused by reduced water content in tendons, ligaments, and cartilage


Thinning of stratum corneum

↓ Langerhans cells, melanocytes, and mast cells

↓ Depth and extent of the subcutaneous fat layer

Thinning and graying of hair caused by more hairs in the resting phase and shortening of the growth phase as well as changes in follicular melanocytes

(DHEA-S, dehydroepiandrosterone-S; GFR, glomerular filtration rate; TSH, thyroid-stimulating hormone.)

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TABLE A2–2: Age-Related Changes in Drug Pharmacokinetics
Pharmacokinetic Phase Pharmacokinetic Parameters
Gastrointestinal absorption

Unchanged passive diffusion and no change in bioavailability for most drugs

↓ Active transport and ↓ bioavailability for some drugs

↓ First-pass metabolism, ↑ bioavailability for some drugs, and ↓ bioavailability for some prodrugs


↓ Volume of distribution and ↑ plasma concentration of water-soluble drugs

↑ Volume of distribution and ↑ terminal disposition half-life (t1/2) for lipid-soluble drugs

Hepatic metabolism

↓ Clearance and ↑ t1/2 for some drugs with poor hepatic extraction (capacity-limited metabolism); phase I metabolism may be affected more than phase II

↓ Clearance and ↑ t1/2 for drugs with high ...

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