Geriatric Physiologic Changes

Physiologic Rhythms, Homeostasis & General Aging Effects

  • Aging disrupts multiple circadian / ultradian rhythms
    • Altered body-temperature regulation; baseline temp slightly lower; febrile responses blunted
    • Flatter diurnal cortisol curve and altered secretion of other hormones → sleep disturbances, fatigue, ↑ stress vulnerability
    • Sleep architecture: ↓ REM & deep‐sleep stages, ↑ nocturnal awakenings, early-morning arousal
  • Cardiovascular/autonomic impacts
    • ↓ Baseline heart rate (≈ 5–65–6 beats/min lost per decade)
    • ↓ Beat-to-beat BP variability; baroreceptors less sensitive → orthostatic hypotension risk
  • Sensory & stress responsiveness
    • Slower reactive & adaptive responses; diminished proprioception & vibration sense → falls
  • Physiologic reserve maximization
    • Organs operate closer to maximal output, leaving little cushion when challenged → frailty syndrome
    • Frailty manifests as weight loss, exhaustion, weakness, slow walking speed, low activity

Integumentary System

  • Structural skin changes
    • Epidermal & dermal thinning; ↓ subcutaneous fat & collagen → wrinkles, laxity, prominent veins
    • Fragile skin, ↑ shear injury & delayed wound healing (slower fibroblast replication)
    • ↓ Sebaceous & eccrine activity → xerosis, pruritus
    • ↓ Melanocytes → gray hair; ↓ vit-D synthetic capacity (osteoporosis risk)
    • Sensory decline: duller perception of touch, vibration, temperature
  • Common benign lesions
    • Seborrheic keratoses: soft, wart-like, "pasted-on" papules, mostly back/trunk, no malignancy risk
    • Senile purpura: non-palpable purple patches on extensor forearm/hand surfaces after minor trauma; fade over weeks, leave brown hemosiderin
    • Lentigines ("liver spots"): tan-brown macules w/ "moth-eaten" borders on dorsum hands/forearms; UV damage; benign
  • Pathologic/precancerous lesions
    • Stasis dermatitis: eczematous changes on lower legs secondary to venous insufficiency; acute weepy plaques/vesicles → chronic hyperpigmentation & ulceration
    • Actinic keratosis: flat/thickened plaques (skin-colored ↔ yellow/white/red), scaly/horny; sun-exposed areas; precursor to squamous cell carcinoma

Ocular System

  • Global age effects
    • Slower light adaptation; glare intolerance; watery eyes (↓ corneal sensitivity)
  • Presbyopia
    • Lens loses elasticity → cannot accommodate near objects; onset early-mid 40s; corrected w/ readers/bifocals
  • Frequent geriatric eye conditions
    • Arcus senilis: bilateral gray-white peripheral corneal ring (lipid deposition); by ≈80 %\approx 80\,\% prevalence at 8080 yrs; if <4040 yrs, evaluate lipids & cardiovascular risk
    • Cataracts
    • Lens clouding (nuclear sclerosis, cortical spoking, posterior capsular haze)
    • Presentation: ↓ night vision, glare, halos, double vision; red reflex → gray/absent in mature cataract
    • Major cause of blindness in developing world; diagnosed w/ fundus exam after dilation
    • Glaucoma
    • Age-related trabecular cell loss → impaired aqueous drainage → ↑ intraocular pressure
    • Angle-closure: acute pain, halos, N/V; emergency
    • Open-angle: insidious peripheral → central field loss; often asymptomatic until late
    • Work-up: tonometry, gonioscopy, visual fields, dilated exam
    • Macular degeneration
    • Degeneration of macula (central retina) → central vision loss, metamorphopsia; #1 irreversible vision loss >6060 yrs
    • Dry (drusen) vs wet (neovascular, rapid)
    • Tools: Amsler grid, OCT, fluorescein angiography

Auditory System

  • Presbycusis (sensorineural)
    • Degeneration of ossicles, hair cells, auditory neurons → high-frequency loss, poor speech discrimination in noise
    • Cerumen impaction more frequent & worsens hearing

Cardiovascular System

  • Structural & functional changes
    • LV concentric hypertrophy, ↓ compliance, ↑ pulmonary capillary wedge pressure
    • Valvular annuli/cusps calcify (esp. aortic & mitral)
    • Aorta dilates/stiffens → ↑ afterload; arteries develop thickened intima & arteriosclerosis → isolated systolic HTN (↑ SBP, normal/low DBP)
  • Autonomic & hemodynamic shifts
    • Blunted baroreflex → orthostatic BP drop
    • ↓ Maximal HR (formula: HRmax=220−ageHR_{max}=220-age overestimates elders)
    • Normal S4 possible >7575 yrs (if no pathology)

Respiratory System

  • Volumes & mechanics
    • Total lung capacity ≈ unchanged; however:
    • ↓ FVC & FEV$_{1}$
    • ↑ Residual volume (loss of elastic recoil, chest‐wall stiffness, flatter diaphragm)
    • Small airway collapse earlier in expiration; breath sounds/crackles at bases may be normal
  • Gas exchange & defense
    • ↓ Response to hypoxia/hypercapnia; ↓ mucociliary clearance; weaker cough (↓ muscle strength)
    • Full lung expansion only when upright

Renal & Fluid-Electrolyte Balance

  • Morphology & GFR
    • Kidney mass ↓ 25!–!30%25!–!30\% (steepest after 5050 yrs); functional glomeruli ↓ ≈50%\approx 50\%
    • Creatinine clearance ↓; but serum creatinine may stay "normal" due to ↓ muscle mass → calculate eGFR
  • Tubular & endocrine effects
    • ↓ Concentrating/diluting ability; impaired Na⁺ conservation; ↑ nephrotoxic risk (e.g., NSAIDs)
    • ↓ Renin & angiotensin II; water/solute handling less adaptable

Genitourinary & Reproductive Systems

  • Bladder
    • ↓ Capacity & compliance; ↓ flow rate; ↑ post-void residual; urinary incontinence prevalence rises
  • Male
    • Benign prostatic hypertrophy (BPH)
    • ↓ Testosterone effect → need ↑ stimulation, fewer spontaneous erections, prolonged refractory interval
    •  Sperm count, motility, ↑ chromosomal abnormalities
  • Female
    • Ovarian failure → ↓ estrogen/progesterone; menopause ~5151 yrs
    • Postmenopausal urogenital atrophy: shortened urethra, weaker sphincter → stress incontinence 2!–!32!–!3× > men
    • Vaginal atrophy, ↑ pH → infection risk; need ↑ stimulation for arousal

Musculoskeletal System

  • Bone & cartilage
    • Bone mass ↓ 0.5%/yr0.5\% / yr; accelerates post-menopause → osteoporosis, fractures, kyphosis, height ↓ 2.5!–!5%2.5!–!5\% by 7070 yrs (faster after)
    • Articular cartilage degeneration >4040 yrs → osteoarthritis (AM stiffness improving w/ activity)
    • Fracture healing slower (↓ osteoblasts)
  • Muscle
    • Sarcopenia: loss begins ≈50≈50 yrs; ↓ fiber number & size → ↓ strength & power; contributes to frailty & falls

Gastrointestinal System & Liver

  • Oral & esophageal
    • Receding gums, xerostomia; ↓ taste bud sensitivity → ↓ appetite
    • ↓ Esophageal compliance & tongue strength → aspiration risk
  • Stomach & intestines
    • Delayed gastric emptying; ↓ prostaglandins → ↑ NSAID gastritis risk
    • Malabsorption: folate, B12B_{12}, Ca²⁺
    • Large bowel transit slower → constipation, laxative abuse; diverticulosis common; colorectal cancer risk ↑ 40!–!5040!–!50 yrs
    • Fecal incontinence multifactorial (sphincter weakness, neurogenic, meds)
  • Liver
    • Mass ↓ 20!–!40%20!–!40\%; blood flow ↓ up to 50%50\%
    • ↓ CYP450 → drug clearance ↓ 20!–!40%20!–!40\%; adjust doses/intervals
    • Slight ↓ serum albumin; LFTs (ALT/AST/ALP) largely unchanged
    • ↑ Lipofuscin & LDL (fewer LDL receptors)

Endocrine System

  • Pancreas: mild atrophy; postprandial hyperinsulinemia, mild peripheral insulin resistance
  • Altered circadian secretion of growth hormone, melatonin etc. → insomnia/phase shifts

Immune System

  • Overall immunosenescence → ↑ infection, cancer, autoimmunity
    • Baseline temp lower; fever may be absent. Atypical infection signs: falls, delirium, anorexia, weakness
  • Adaptive immunity > innate decline
    • T cells: ↓ numbers, clonal expansion, signaling → impaired cellular immunity
    • B cells: ↓ bone-marrow precursors, peripheral counts → weaker humoral responses, ↓ vaccine efficacy
  • Cytokine production diminished

Hematologic System

  • RBC life span, blood volume, leukocyte count unchanged
  • Bone marrow
    • Mass ↓; fat ↑; hematopoietic reserve ↓
    • Slower compensation to bleeding/hypoxia
  • Platelets more responsive → ↓ bleeding time; ↑ thrombus/embolus risk

Neurologic System

  • Hallmarks
    • Slowed reaction & processing; ↓ proprioception; falls
    • Executive function & attention decline (pronounced >7070 yrs) despite stable general cognition absent disease
  • Physical exam variations
    • DTRs may be brisk or absent; cranial-nerve sensory thresholds ↑
    • Medication effects may mimic neuropathology (e.g., sedatives prolong reflex times)

Pharmacologic Considerations (Beers Criteria Perspective)

  • Absorption & distribution
    • Slow gastric emptying, ↑ gastric pH → altered bioavailability
    • ↑ Fat/Muscle ratio → larger Vd for lipophilic drugs (e.g., diazepam)
    • ↓ Serum albumin → ↑ free fraction of highly protein-bound drugs (warfarin, phenytoin)
  • Metabolism & elimination
    • ↓ Hepatic CYP450 & renal GFR/CrCl → prolonged half‐lives; rely on eGFR not serum creatinine alone
  • Pharmacodynamics
    • ↑ CNS sensitivity to benzodiazepines, anticholinergics, hypnotics, TCAs, antihistamines, antipsychotics
    • Anticholinergic adverse effects: constipation, urinary retention (caution with BPH), blurred vision, dry mouth, orthostatic hypotension
  • Polypharmacy
    • Multiple comorbidities → ↑ risk adverse drug events, falls, cognitive decline; regular med reconciliation essential
    • Beers Criteria: evidence-based list of potentially inappropriate meds for ≥6565 yrs