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Respiratory System Physiology - Anatomy & Physiology

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  • Phases of pulmonary ventilation
    Inspiration: gases flow into lungs; Expiration: gases exit lungs.
  • Atmospheric pressure (Patm)
    Pressure exerted by air surrounding the body; 760 mm Hg at sea level equals 1 atmosphere.
  • Intrapulmonary pressure (Ppul)
    Pressure inside alveoli; fluctuates with breathing and eventually equals atmospheric pressure.
  • Intrapleural pressure (Pip)
    Pressure in pleural cavity; always negative, usually 4 mm Hg less than Ppul, prevents lung collapse.
  • Forces promoting lung collapse
    1) Elastic recoil of lungs; 2) Surface tension of alveolar fluid pulling alveoli smaller.
  • Force opposing lung collapse
    Elasticity of chest wall pulling thorax outward, maintaining negative intrapleural pressure.
  • Transpulmonary pressure
    Difference between intrapulmonary and intrapleural pressure (\(P_{pul} - P_{ip}\)); keeps lungs open.
  • Atelectasis
    Lung collapse caused by plugged bronchioles or pneumothorax; treated by removing air with chest tubes.
  • Boyle's law in pulmonary ventilation
    Pressure of a gas varies inversely with volume: \(P_1V_1 = P_2V_2\).
  • Muscles involved in inspiration
    Diaphragm (contracts and flattens) and external intercostals (lift rib cage) increase thoracic volume.
  • Pressure changes during inspiration
    Intrapulmonary pressure drops below atmospheric pressure, causing air to flow into lungs.
  • Forced inspiration muscles
    Accessory muscles: scalenes, sternocleidomastoid, pectoralis minor, and erector spinae increase thoracic cage size.
  • Expiration process
    Usually passive; inspiratory muscles relax, thoracic volume decreases, intrapulmonary pressure rises above atmospheric, air flows out.
  • Forced expiration muscles
    Oblique and transverse abdominal muscles and internal intercostals actively decrease thoracic volume.
  • Airway resistance and gas flow relationship
    Gas flow (F) is proportional to pressure difference (∆P) and inversely proportional to resistance (R): \(F = \frac{\Delta P}{R}\).
  • Alveolar surface tension
    Attraction of liquid molecules in alveoli that tends to collapse alveoli; reduced by surfactant.
  • Surfactant
    Detergent-like lipid-protein complex produced by type II alveolar cells; reduces surface tension and prevents alveolar collapse.
  • Lung compliance
    Measure of lung stretchability; higher compliance means easier lung expansion.
  • Lung compliance formula
    \(C_L = \frac{\Delta V_L}{\Delta (P_{pul} - P_{ip})}\), where CL is compliance, ΔVL is change in lung volume.
  • Respiratory volumes: Tidal volume (TV)
    Amount of air moved in and out of lungs with each breath; averages about 500 ml.
  • Inspiratory reserve volume (IRV)
    Amount of air that can be forcibly inspired beyond tidal volume (2100–3200 ml).
  • Expiratory reserve volume (ERV)
    Amount of air that can be forcibly expelled from lungs (1000–1200 ml).
  • Residual volume (RV)
    Amount of air remaining in lungs after forced expiration; keeps alveoli open.
  • Vital capacity (VC)
    Sum of tidal volume, inspiratory reserve volume, and expiratory reserve volume (TV + IRV + ERV).
  • Anatomical dead space
    Air in conducting passages (~150 ml) that does not participate in gas exchange.
  • Dalton's law of partial pressures
    Total pressure of gas mixture equals sum of partial pressures of individual gases.
  • Henry's law
    Gas dissolves in liquid proportional to its partial pressure; solubility and temperature affect amount dissolved.
  • External respiration
    Gas exchange between alveoli and blood influenced by partial pressure gradients, membrane thickness, and ventilation-perfusion coupling.
  • Ventilation-perfusion coupling
    Matching of alveolar ventilation and pulmonary blood flow controlled by local PO2 and PCO2 affecting arteriole and bronchiole diameters.
  • Internal respiration
    Gas exchange between blood and body tissues; oxygen moves from blood to tissues, CO2 moves from tissues to blood.