Pleural Fluid and Its Functions

  • Purpose of Pleural Fluid:

    • Reduces friction during lung expansion and contraction.

    • Ensures smooth movement of lungs against thoracic cavity.

  • Pleural Effusion:

    • Accumulation of excess fluid in the pleural cavity due to inflammation.

    • Causes chest pain due to pleura rubbing (pleurisy).

Pressure Dynamics in the Respiratory System

  • Pressure Types:

    • Atmospheric Pressure:

    • Standard value: 760 ext{ mmHg}.

    • Intrapleural Pressure:

    • Pressure within the pleural cavity.

    • Intra-alveolar (Intrapulmonary) Pressure:

    • Pressure within the lungs.

  • Pressure Gradient:

    • Air flows from high pressure (atmospheric) to low pressure (intrapulmonary).

    • Flow of Air:

    • Directly proportional to pressure difference and inversely proportional to resistance.

  • Breathing Mechanics:

    • Inspiration:

    • Intrapulmonary pressure decreases (negative relative to atmospheric pressure).

    • Volume within the lungs increases, pressure decreases: This follows Boyle's Law:

      • V imes P = k (constant).

    • Expiration:

    • Intrapulmonary pressure increases, leading to a decrease in lung volume.

Pleural Pressures and Breathing Mechanics

  • Function of Pleura:

    • Parietal Pleura: Pulls lungs outward.

    • Visceral Pleura: Pulls lungs inward.

    • Negative pressure is maintained even at rest to prevent lung collapse.

Effect of Trauma on Lung Dynamics

  • Stab Wound/Trauma:

    • Introduces air into pleural cavity, altering negative pressure that keeps the lung inflated, leading to a lung collapse (pneumothorax).

  • Hemothorax: Blood accumulation in the pleural cavity due to trauma.

    • Treatment: Chest tube insertion to drain fluid/air.

Mechanics of Breathing

  • Ventilation Defined: Whole process of inspiration and expiration.

  • Pathway of Air: Nose → Pharynx → Larynx → Trachea → Bronchi (Primary, Secondary, Tertiary) → Bronchioles → Alveoli.

  • Resistance in Airways: Resembles that in blood vessels, hence as bronchioles constrict, resistance increases, potentially limiting airflow.

Division of Respiratory Zones

  • Conducting Zone:

    • No gas exchange; includes nose, larynx, trachea, and bronchi (composed of cartilage).

  • Respiratory Zone:

    • Contains respiratory bronchioles and alveoli where gas exchange occurs.