Video 3 - Respiration & Pulmonary Physiology – Core Vocabulary

Mechanics of Breathing (Boyle’s Law in Action)

• Expansion of thoracic cavity ⇨ ↑ volume, ↓ pressure (Boyle’s Law) ⇨ air rushes in.

  • Inspiration = active; expiration = usually passive.

• Compression of thoracic cavity ⇨ ↓ volume, ↑ pressure ⇨ air flows out.

• Pleural linkage

  • Lungs are NOT glued to ribs/diaphragm; they “follow” chest wall because intrapleural pressure remains slightly negative.

  • Explains how delicate alveolar tissue is ventilated without direct muscular attachments.

Diaphragm & Intercostal Contributions

• Diaphragm

  • Contracts (flattens & pulls downward) during inhalation.

  • Relaxes (domes upward) during passive exhalation.

• External intercostals

  • Lift ribs “up & out” like a bucket-handle, enlarging rib cage.

• Forced exhalation muscles

  • Internal intercostals: pull ribs “down & in.”

  • Abdominal group (e.g., rectus abdominis): push diaphragm up, rapidly expelling air.

• Exercise/Winded state ⇨ recruits these additional muscles for rapid ventilation.

Balloon-Bottle Model Demonstration

• Components

  • 2-liter bottle = thoracic cage.

  • Red balloons = lungs (no contact with bottle walls).

  • Y-shaped straw = trachea + primary bronchi.

  • Stretched green balloon across cut bottom = diaphragm.

• Observations

  • Pull green balloon downward (↑ volume) ⇨ red balloons inflate.

  • Release/push upward (↓ volume) ⇨ red balloons deflate.

• Significance: visually separates lung tissue from chest wall, reinforcing pressure-based, not traction-based, ventilation.

Gas Exchange Principles

• Assume constant body temperature.

• Two key determinants of diffusion rate across respiratory membrane:

  • Partial-pressure gradients (concentration differences)

  • Solubility of gas in fluid.

• Respiratory membrane characteristics

  • Huge surface area (alveolar “raspberry” morphology).

  • Thickness ≈ 2 cell layers ⇒ minimal diffusion distance.

Representative Partial-Pressure Values (mm Hg)

• \Delta P{O2} = 105 - 40 = 65\;\text{mm Hg} ⇒ strong drive into blood.

• \Delta P{CO2} = 46 - 40 = 6\;\text{mm Hg} but high solubility lets it diffuse efficiently.

Hemoglobin & Oxygen Transport

• Structure

  • Tetramer = 4 globin chains (2 α, 2 β) each with a heme-Fe “bracket.”

  • Fe required for heme synthesis ⇒ dietary iron critical.

• Capacity: 1 Hb molecule binds 4 O_2 molecules.

• Loading (lungs): Hb + 4O2 \rightarrow Hb(O2)_4 (oxyhemoglobin).

• Unloading (tissues): reverse reaction producing deoxyhemoglobin.

• Affinity balance

  • Bond must be strong enough for transport yet weak enough for release.

Oxyhemoglobin Dissociation Curve (simplified)

• X-axis: P{O2}; Y-axis: % saturation.

• Between 100 \rightarrow 40\;\text{mm Hg}, saturation only drops from ~100 % → 75 % ⇒ buffer for normal activity.

• Below 40\;\text{mm Hg}, curve steepens → rapid O₂ unloading in hypoxic tissues.

Carbon Monoxide (CO) Competition

• Hb affinity for CO ≈ 200× that for O_2.

• Formation of carboxyhemoglobin (CO-Hb) is essentially irreversible under normal alveolar P{O2}.

• Sources & implications

  • Faulty heaters, indoor generators, cigarette smoke.

  • Symptoms: headache, drowsiness → lethal hypoxia during sleep.

  • Ethical/Practical: importance of home CO detectors & public-health education.

• Treatment: immediate high-flow O_2 or hyperbaric oxygen to displace CO.

Carbon Dioxide Transport (3 Forms)

1. \approx 90\% as bicarbonate system

   • CO2 + H2O \leftrightarrow H2CO3 \leftrightarrow HCO_3^- + H^+

   • Rapid, enzyme-mediated (carbonic anhydrase in RBCs).

   • Chloride shift exchanges Cl^- for HCO_3^- to maintain charge balance.

2. \approx 5\% bound reversibly to globin (carbaminohemoglobin).

3. \approx 5\% dissolved directly in plasma.

• Physiological implication: bicarbonate acts as major blood buffer (acid-base homeostasis).

Breathing Patterns & Terminology

• Eupnea (quiet breathing)

  • Passive exhalation via elastic recoil.

• Hyperpnea (forced/active breathing)

  • Requires internal intercostals + abdominal muscles for vigorous exhalation.

• Apnea = transient cessation of breathing (e.g., cold shock, sudden pain, sleep apnea).

Quantitative Respiratory Measurements

• Respiratory Rate (f): breaths ∙ min^{-1}.

• Tidal Volume (TV): air per normal breath (~500 mL).

• Dead-space / Residual Volume (RV): air in conducting zone never reaching alveoli.

  • Standard assumption: 1000\;\text{mL} (females) or 1200\;\text{mL} (males).

Alveolar Ventilation Rate

\text{AVR} = (TV - RV) \times f

• Example: f = 12\;\text{min}^{-1},\; TV = 500\;\text{mL},\; RV = 150\;\text{mL}

  • AVR = (500 - 150) \times 12 \approx 4\;\text{L·min}^{-1}.

Volumes & Capacities

• Inspiratory Reserve Volume (IRV): extra air inhalable after normal inspiration.

• Expiratory Reserve Volume (ERV): extra air exhalable after normal expiration.

• Vital Capacity (VC): TV + IRV + ERV.

• Total Lung Capacity (TLC): VC + RV.

  • On exams, RV is supplied or assumed; missing variables solvable algebraically.

Factors That Modify Respiration

• Sudden pain / cold splash → apnea.

• Chronic pain → ↑ respiratory rate (diagnostic clue in hospice/ICU).

• Fever (↑ body temperature) → ↑ respiratory rate (heat dissipation).

• Hypothermia → ↓ respiratory rate (overall metabolic slowdown).

Compliance, Elasticity & Surfactant

• Lung compliance normally high due to elastic fibers + surfactant that reduces alveolar surface tension.

• Pathologies lowering compliance (e.g., fibrosis, pregnancy-induced restriction) force accessory muscle use.

Pressure Flow Summary

• Muscle action alters thoracic \rightarrow intrapulmonary/intrapleural pressures.

• Air flows from high → low pressure, enabling ventilation.

• O2 moves down its steep partial-pressure gradient; CO2 moves primarily due to high solubility.

Real-World & Ethical Connections

• Safety: CO detectors, generator placement, smoking cessation campaigns.

• Clinical practice: monitoring respiratory rate for pain, fever, or drug overdose.

• Sports/rehab: training respiratory muscles for better vital capacity, forced-exhalation strength.

Next Steps (per instructor): Complete respiratory quiz before starting urinary module.