Transport of Oxygen and Carbon Dioxide

Oxygen Transport 🩸

  • 97% of O₂ is carried by red blood cells (RBCs) using hemoglobin.
  • Only 3% dissolves directly in plasma.
  • Hemoglobin binds O₂ to form oxyhemoglobin (each hemoglobin carries up to 4 O₂ molecules!).
  • Binding depends on:
    • O₂ partial pressure (pO₂) – main factor
    • CO₂ partial pressure (pCO₂)
    • H⁺ concentration (acidity)
    • Temperature 🌡️
  • Oxygen dissociation curve (sigmoid curve) shows how hemoglobin saturation changes with pO₂.
  • In lungs: High pO₂ + low pCO₂ + low H⁺ + cool → O₂ binds hemoglobin.
  • In tissues: Low pO₂ + high pCO₂ + high H⁺ + warm → O₂ releases from hemoglobin.
  • 100 ml oxygenated blood gives tissues ~5 ml O₂.

Carbon Dioxide Transport 💨

  • 20-25% binds hemoglobin → carbamino-hemoglobin.
  • 70% travels as bicarbonate (HCO₃⁻) in blood.
  • 7% dissolves in plasma.
  • Binding depends on pCO₂ and pO₂:
    • Tissues: High pCO₂ + low pO₂ → CO₂ binds hemoglobin.
    • Lungs: Low pCO₂ + high pO₂ → CO₂ releases from hemoglobin.
  • Carbonic anhydrase (enzyme in RBCs) speeds up this reaction: \[ \ce{CO2 + H2O <=> H2CO3 <=> H+ + HCO3^-} \]
  • At tissues: CO₂ → HCO₃⁻ for transport.
  • At lungs: HCO₃⁻ → CO₂ (exhaled!).
  • 100 ml deoxygenated blood releases ~4 ml CO₂ in lungs.

Regulation of Breathing 🧠

  • Respiratory rhythm centre (medulla brain) sets breathing pace.
  • Pneumotaxic centre (pons brain) fine-tunes rhythm → shortens inhales.
  • Chemosensitive area (near rhythm centre) detects ↑CO₂/H⁺ → signals to adjust breathing and remove excess CO₂.
  • Aortic/carotid artery sensors also detect CO₂/H⁺ changes → alert rhythm centre.
  • Note: Oxygen levels play a minor role in regulating breathing.

Respiratory Disorders 😷

  • Asthma: Wheezing due to swollen bronchi/bronchioles.
  • Emphysema: Alveoli walls break down → less gas exchange surface. Main cause: Smoking 🚬.

NEET Quick Tips! 🎯

  1. O₂ dissociation curve: Sigmoid shape + how pCO₂/H⁺/temp shift it.
  2. CO₂ transport: % as carbamino-hemoglobin vs. bicarbonate.
  3. Carbonic anhydrase: Converts CO₂ ↔ HCO₃⁻ (reversible!).
  4. Breathing control: Role of medulla/pons + chemosensors for CO₂.
  5. Emphysema: Alveolar damage → reduced surface area (smoking link!).

Keep revising – you’re getting closer to acing this! 💪