Lecture Notes: Respiratory Volumes and Gas Exchange

Lung Volumes

• Tidal Volume:
  • Quiet breathing moves about 0.5 liters (a pint) of air in and out.
  • Small relative to total lung volume (about 5 liters).
• Inspiratory Reserve Volume:
  • Additional 2.5 liters can be inhaled after a quiet inhalation.
• Expiratory Reserve Volume:
  • About 1.5 liters can be exhaled beyond a normal exhalation.
• Vital Capacity:
  • Total volume from full inhalation to full exhalation.
  • Measure with a spirometer.
• Residual Volume:
  • Gas remains in lungs after full exhalation (~1,200 mL).
• Anatomical Dead Space:
  • Air in passages not used for gas exchange (~150 mL).

Alveolar Structure and Function

• Alveoli: Air sacs in lungs.
  • Type I Pneumocytes: Thin cells for gas exchange.
  • Type II Pneumocytes: Secrete surfactant to reduce surface tension, prevent collapse.
  • Dust Cells: Alveolar macrophages that clean alveoli.
• Surfactant:
  • Important for newborn viability.
  • Synthetic surfactant available now.

Gas Exchange

• Partial Pressure: Driving force for gas exchange.
  • Oxygen and other gases in air contribute to total air pressure.
  • Difference in partial pressures drives oxygen into blood, carbon dioxide out.
• Oxygen Transport:
  • Carried by hemoglobin in red blood cells.
  • Oxygen Dissociation Curve:
    • Factors affecting oxygen release: Low pH, high temperature, high CO2, presence of 2,3-BPG.
• Carbon Monoxide:
  • Binds to hemoglobin more strongly than oxygen, leading to poisoning.

Respiratory Control

• Brain Centers:
  • Medulla Oblongata: Controls rhythmic breathing.
  • Pons: Fine-tunes breathing depth and force.
• Chemoreceptors:
  • Located in aorta, carotid arteries, and CNS.
  • Monitor CO2, O2, and pH in blood.
• Factors Influencing Breathing:
  • Emotional state, physical activity, environmental temperature.

Hypoxia

• Signs:
  • Cyanosis (blue discoloration) indicates low oxygen in tissues.
  • Clubbing of fingers may indicate chronic hypoxia.

This lecture covered the mechanics of lung volumes, the role of various types of cells in the alveoli, and the physiological mechanisms of gas exchange and respiratory control.