Pathophysiology Exam 3 – Rapid Review Notes

Pulmonary System Anatomy

• Upper (conducting) portion: naso/oro/laryngopharynx
• Lower (respiratory) portion: larynx → trachea → bronchi → bronchopulmonary segments → alveoli
• Blood supply: bronchial & pulmonary arteries
• Alveolar cells: type I (gas exchange); type II (surfactant ↓ surface tension)

Neural Control & ANS Effects

• Respiratory centers: pons & medulla; efferent via phrenic nerve
• Parasympathetic (acetylcholine, vagus) → bronchoconstriction
• Sympathetic (β₂-adrenergic, epinephrine) → bronchodilation

Mechanics of Breathing

• Inspiration: diaphragm & external intercostals contract → ↑thoracic volume → negative intrapleural pressure
• Expiration: passive; active (forceful) uses internal intercostals & abdominals
• Functional residual capacity = air left after normal expiration
• Surfactant keeps alveoli open

Airway Resistance & Compliance

• Resistance ∝ \frac{1}{\text{radius}^4}; highest at nose, lowest in small bronchioles
• ↑Resistance factors: mucus, bronchospasm, stress, aging
• Compliance = \frac{\Delta V}{\Delta P}; ↑ in neonates, ↓ with age (rigid chest, ↓elastic fibers)

Ventilation & Diffusion

• Distribution: greatest at lung bases (upright)
• Diffusion barriers: surfactant → RBC (6 layers)
• Hypoventilation → ↑PaCO2 (resp. acidosis); Hyperventilation → ↓PaCO2 (resp. alkalosis)

Obstructive vs Restrictive Patterns

• Obstructive: air OUT problem (↑resistance, wheeze, hyperinflation)
• Restrictive: air IN problem (↓compliance, ↓volumes, crackles)

Obstructive Disorders

• Asthma (reversible)

• Intrinsic (non-allergic, adult); Extrinsic (IgE-mediated, pediatric)
• Immediate mediators: histamine, leukotrienes, prostaglandins
• S/S: wheeze, cough, tight chest, dyspnea
• Dx: ↓PEFR/FEV₁; Tx: trigger avoidance, β₂-agonists, steroids, O₂
  • Chronic Bronchitis (Type B COPD, “blue bloater”)
• Productive cough >3 mo/yr for 2 yrs
• Patho: mucous-gland hyperplasia, thick wall, pulmonary HTN
• S/S: cough, sputum, edema, cyanosis
• Tx: stop smoking, bronchodilators, hydration
  • Emphysema (Type A COPD, “pink puffer”)
• Alveolar wall destruction, loss of recoil; α₁-antitrypsin deficiency or smoking
• S/S: dyspnea, thin, barrel chest, pursed-lip breathing
• PFT: ↓FEV₁, ↑TLC; CXR: hyperinflation
• Tx: O₂, anticholinergics, steroids
  • Bronchiectasis: irreversible bronchial dilation post‐infection; copious purulent sputum
  • Cystic Fibrosis: AR CFTR mutation → thick secretions, recurrent infections

Restrictive Parenchymal Disorders

• Diffuse Interstitial Lung Disease (fibrotic)

• Immune injury → inflammation → fibrosis
• S/S: exertional dyspnea, dry cough, bibasilar crackles, clubbing
  • Sarcoidosis: non-caseating granulomas; young women; S/S: fatigue, skin lesions; Tx: steroids
  • ARDS: acute alveolar-capillary damage (sepsis, trauma, aspiration)
• Patho: leaky capillaries → non-cardiogenic pulmonary edema, surfactant loss
• Hallmark: severe hypoxemia refractory to O₂; CXR “white-out”

Neuromuscular / Chest-Wall Causes

• Poliomyelitis, ALS, Guillain-Barré, Myasthenia gravis → ventilatory failure
• Deformities: kyphoscoliosis, flail chest, obesity restrict expansion

Pulmonary Infections

• Pneumonia: alveolar inflammation by bacteria/virus/aspiration
  • S/S: fever, crackles, purulent sputum; CXR infiltrate; Tx: antibiotics
• SARS, TB also impact respiration (not detailed here)

Fluid & Electrolyte Basics

• Homeostasis: intake, absorption, distribution, excretion
• Regulators: hypothalamic thirst/ADH, RAAS, natriuretic peptides
• Edema mechanisms: ↑hydrostatic P, ↓oncotic P, lymph block, Na/H₂O retention

Key Electrolyte Ranges & Imbalance Signs

• Sodium 135–145 mEq/L
  • Hyponatremia: cramps, confusion • Hypernatremia: thirst, dry mucosa
• Potassium 3.5–5 mEq/L
  • Hypo: weakness, arrhythmia • Hyper: flaccid paralysis, arrest
• Calcium 8.5–10.5 mg/dL
  • Hypo: tetany, spasms • Hyper: lethargy, constipation
• Magnesium 1.5–2.5 mEq/L
  • Hypo: cramps, arrhythmia • Hyper: ↓reflexes, respiratory depression
• Chloride 98–108 mEq/L; Phosphate 2.5–4.5 mg/dL (see symptoms as needed)

Acid–Base Quick Table

High-Yield Reminders

• Surfactant from type II cells critical for alveolar stability
• \text{Resistance} \uparrow as airway radius ↓; neonates have naturally higher resistance
• COPD hallmark: ↓FEV₁/FVC ratio; Restrictive: ↓TLC with normal ratio
• ARDS: treat underlying cause & provide supportive oxygenation
• RAAS ↑Na⁺/water reabsorption; Natriuretic peptides oppose RAAS
• Buffer systems (Hb, bicarbonate) & lungs/kidneys maintain pH 7.35–7.45