5.6 Respiratory System

1. Structures of the Respiratory System

  • Upper Respiratory Tract: Nose/Nasal Cavity, Pharynx, Larynx (Voice Box).
  • Lower Respiratory Tract: Trachea (Windpipe), Bronchi, Bronchioles, Lungs, Alveoli (Air Sacs), Pleura.

2. Mechanism of Breathing (Ventilation)

  • Inspiration (Inhaling):
    • Diaphragm contracts (moves down).
    • External intercostal muscles contract (ribs up/out).
    • Thoracic volume increases, intrapulmonary pressure decreases.
    • Air flows into lungs.
  • Expiration (Exhaling):
    • Diaphragm and external intercostal muscles relax.
    • Thoracic volume decreases, intrapulmonary pressure increases.
    • Air flows out of lungs.

3. Tissue Respiration (Cellular Respiration)

  • Metabolic process where cells break down organic molecules (glucose) to release energy (ATP).
  • Process: Glucose + Oxygen → Carbon Dioxide + Water + Energy (ATP) + Heat.
  • Heat Production: Exothermic process, crucial for maintaining body temperature.

4. Anaerobic Respiration: Plants vs. Humans

Feature Plants (Alcoholic Fermentation) Humans (Lactic Acid Fermentation)
Conditions Oxygen scarce (e.g., waterlogged soil, yeast) Intense physical activity (insufficient O₂ supply)
Equation Glucose → Ethanol + CO₂ + ATP Glucose → Lactic Acid + ATP
End Products Ethanol, CO₂ Lactic Acid

5. Gaseous Transport

  • Oxygen Transport:
    • ~97% bound to Hemoglobin (oxyhemoglobin) in RBCs.
    • ~3% dissolved in plasma.
  • Carbon Dioxide Transport:
    • ~70% as Bicarbonate Ions (HCO₃⁻) in plasma.
    • ~20-25% as Carbaminohemoglobin (bound to Hb).
    • ~7-10% dissolved in plasma.

6. Respiratory Volumes and Capacities

  • Tidal Volume (TV): Normal breath (~500 mL).
  • Inspiratory Reserve Volume (IRV): Max air inhaled after normal inspiration.
  • Expiratory Reserve Volume (ERV): Max air exhaled after normal expiration.
  • Residual Volume (RV): Air remaining in lungs after max exhalation.
  • Vital Capacity (VC): Max exchangeable air (TV + IRV + ERV).
  • Total Lung Capacity (TLC): Max air lungs can hold (VC + RV).

7. Effect of Altitude on Breathing

  • Lower atmospheric PO₂ at high altitudes makes oxygen intake challenging.
  • Immediate Responses (Acclimatization): Increased breathing rate (hyperventilation), increased heart rate.
  • Long-Term Adaptations: Increased red blood cell production, increased capillary density, increased myoglobin.

8. Asphyxiation and Hypoxia

  • Asphyxiation (Suffocation): Severe O₂ deficiency due to interference with breathing process (e.g., airway obstruction).
  • Hypoxia: Insufficient O₂ supply at the tissue level.
    • Causes: Low blood O₂ (hypoxemic), reduced O₂-carrying capacity (anemic), inadequate blood flow (ischemic), tissues unable to use O₂ (histotoxic).