Airways & Alveoli Video Lecture Notes

The Airways and Alveoli Overview

• Upper Airways

  • Part of the conducting airways.

  • Function: Connect atmospheric air to the gas-exchanging areas of the lungs.

  • No gas exchange occurs in these airways; role is to provide passage for air.

  • Additional Functions:

    • Warming the incoming air.

    • Humidifying the air.

    • Filtering the air.

  • Components:

    • Nose

    • Oral Cavity

    • Pharynx (Throat)

      • Divided into three sections:

      • Nasopharynx

      • Oropharynx

      • Laryngopharynx

    • Larynx (Voice Box)

      • Marks transition from upper to lower airways.

      • Important for preventing aspiration of foreign materials into the lower airways.

      • Reflexes for Protection:

      • Pharyngeal Reflex: Gag reflex helps expel foreign bodies.

      • Laryngeal Reflex: Causes laryngospasm, closing vocal cords.

• Distinction Between Respiration and Ventilation

  • Respiration: Cellular gas exchange process, comprising two types:

  • External Respiration: Gas exchange in the lungs.

  • Internal Respiration: Exchange of gases in body tissues.

  • Ventilation: Mechanical movement of air in and out of the lungs.

  • Measurement of Ventilation: Carbon dioxide (CO2) levels can indicate ventilation effectiveness:

    • Hypoventilation: High CO2 levels.

    • Hyperventilation: Low CO2 levels.

• Functions of the Nose and Nasal Cavity

  • Critical for warming, humidifying, and filtering air.

  • Heat Moisture Exchanger (HME):

    • Device used in respiratory care to replicate nose functions, providing warmth, humidity, and filtration.

    • Nicknamed "nose" due to its important role.

• Pharynx Structure

  • Three Sections:

    • Nasopharynx

    • Oropharynx

    • Laryngopharynx

      • Larynx: Comprised of cartilage types:

        • Thyroid Cartilage: Largest, anterior covering.

        • Cricoid Cartilage: Only complete ring; narrowest part of an infant's airway.

        • Epiglottic Cartilage: Above the larynx; critical landmark during intubation.

        • Cricothyroid Membrane: Separates thyroid from cricoid cartilage.

• Histology of the Respiratory System

  • Cellular Composition:

  • Majority of nasal cavity and tracheobronchial tree lined with Ciliated Pseudostratified Columnar Epithelium.

  • Simple Squamous Epithelium lines alveoli for efficient gas exchange.

  • Mucociliary Clearance Mechanism:

    • Utilizes mucus blanket and cilia to expel foreign particles.

    • Goblet cells and submucosal glands produce mucus with daily secretion of approximately 100 mL.

  • Optimal Conditions for Mucociliary Clearance:

    • Gas warmed to 37°C.

    • 100% relative humidity.

  • When bypassing the upper airway, we must replace these functions (warm, filter, and humidify gas delivered to a patient with an artificial airway).

• Lower Airways

  • Trachea:

    • Length: Approximately 11-13 cm.

    • Composed of 16-20 C-shaped cartilage rings (anterior).

• Conducting Zone: No gas exchange.

  • Bifurcation of trachea at the Carina into right and left main stem bronchi:

  • Right main stem bronchus: Wider, higher risk for aspiration.

  • Requirement for intubation: Tube should be above carina (2 inches).

  • Further branching into lobar bronchi, segmental bronchi, and down to non-cartilaginous bronchioles.

• Respiratory Zone: Gas exchange occurs.

  • Structures:

  • Respiratory Bronchioles

  • Alveolar Ducts

  • Alveolar Sacs

  • Oxygen travels from alveoli into pulmonary capillary blood, while CO2 is expelled.

• Respiratory Ducts and Alveoli

  • Conducting and Respiratory Zones:

  • Conducting zone leads to respiratory zone where gas exchange occurs.

  • Additional structures aiding in Collateral Ventilation:

  • Canals of Lambert: Connect terminal bronchioles to alveolar sacs.

  • Pores of Kohn: Openings between adjacent alveoli.

  • Alveolar Population: Up to 300,000,000 alveoli in adults.

  • Maximum gas-exchanging surface area comparable to half a tennis court.

  • Alveolar Cells:

  • Type I Cells (Pneumocytes): Thin cells for gas exchange.

  • Type II Cells (Pneumocytes): Produce surfactant to lower surface tension.

  • Type III Cells (Macrophages): Protect alveoli from foreign particles.

  • Alveolar Capillary Membrane: Thin and highly permeable for gas exchange. Gases cross membranes between alveoli and pulmonary capillary blood.

• Gas Exchange Process

  • Oxygen enters the blood; CO2 moves from blood to alveoli for exhalation.