9.04 Inhaled Air

1. Warming and Moistening of Inhaled Air

Purpose

• Temperature Regulation: As air passes through the nose and trachea, it is warmed to match the body’s internal temperature.
• Moisturization: Evaporation adds moisture to the inhaled air.

Function

• Protection of Lungs: Prevents the delicate lung tissues from drying out (desiccation), ensuring optimal function and preventing irritation.

2. Filtration and Cleaning of Inhaled Air

Purpose

• Defense Against Harmful Particles: Inhaled air can carry harmful substances such as dust, sand, pollen, fungal spores, bacteria, and viruses that can damage lung tissue.

Mechanisms for Trapping Particles

Nose Hairs and Mucus

• Function:
  • Nose Hairs: Trap larger particles (>5–10 μm) present in the inhaled air.
  • Mucus Lining: Captures and holds these particles, preventing them from reaching the lower airways.

Goblet Cells and Mucus Production

• Location: Present in the ciliated epithelium of the trachea and bronchi.
• Structure:
  • Goblet Cells: Named for their goblet-like shape, these cells have an upper portion swollen with mucin droplets.
• Mucin:
  • Composition: A glycoprotein that imparts stickiness to mucus.
  • Function: Traps inhaled particles, making them easier to remove.
• Additional Mucus Sources: Mucous glands beneath the epithelium also produce mucus, enhancing the trapping capability.

Ciliated Epithelial Cells

• Structure: Epithelial cells equipped with hair-like structures called cilia.
• Function:
  • Mucus Transport: Cilia beat in a coordinated, wave-like motion, moving the mucus laden with trapped particles upward toward the larynx at a rate of approximately 1 cm/min.
  • Particle Removal: Transports trapped particles and pathogens to the throat, where they are swallowed and destroyed by stomach acid.

3. Role of Smooth Muscle in Bronchioles

Structure

• Location: Surrounds the bronchioles within the lungs.
• Composition: Contains smooth muscle fibers without cartilage support.

Function

• Airflow Regulation:
  • Contraction: Narrows the bronchiole diameter, reducing airflow.
  • Relaxation: Widens the bronchiole diameter, increasing airflow.
• Dynamic Adjustment:
  • During Exercise: Smooth muscles relax to allow a greater volume of air to reach the alveoli, accommodating increased oxygen demand.
• Flexibility: Absence of cartilage permits the bronchioles to adjust their diameter as needed, providing greater control over airflow distribution.

4. Protection Against Airborne Pollutants and Pathogens

Chemical Pollutants

• Examples: Sulfur dioxide, nitrogen dioxide.
• Impact:
  • Mucus Interaction: These pollutants can dissolve in mucus, forming acidic solutions.
  • Irritation: Acidic mucus can irritate the airway linings, leading to inflammation and discomfort.

Phagocytic Cells (Macrophages)

• Location: Patrol the surfaces of the airways.
• Function:
  • Engulfment: Engulf and remove small particles, including bacteria and fine dust.
  • Pathogen Clearance: Play a crucial role in the immune response by eliminating inhaled pathogens.
• Response to Infection:
  • Immune Activation: During infections, additional phagocytic white blood cells migrate from capillaries to assist in removing pathogens, enhancing the body’s defense mechanisms.