Respiratory System Review

Capillary Permeability and Inflammation

• Increased blood flow leads to pain and swelling.
• This occurs due to:
  • Capillary permeability becoming leaky.
  • Fluid leaks from capillaries into interstitial space, causing swelling.
• Pain is generated due to increased pressure in the swollen area.

Role of Interferons in Viral Infection

• Infected cells release interferons.
• Interferons bind to non-infected cells, preventing viral replication.
• The infected cell sacrifices itself to protect neighboring non-infected cells.

Immune Response: NK Cells and Cytotoxic T Cells

• Key players in cellular immunity include:
  • NK (Natural Killer) Cells: Involved in early defense against virally infected cells.
  • Cytotoxic T Cells: Target and kill infected cells.
• Perforins:
  • Insert pores into the membranes of pathogens.
• Granzymes: Enter through the pores to induce apoptosis in infected cells.

Plasma Cells and Antibody Production

• B Cells: Upon activation, differentiate into plasma cells.
• Function of Plasma Cells: Produce antibodies that protect against pathogens.

Activation of T Cells

• For T cells to activate, two critical steps must occur:
  1. Antigen binding to T cell receptors.
  2. Co-stimulation signals from other immune cells.

Anatomy of the Respiratory System

• Trachea: Positioned anteriorly in the neck, supported by C-shaped cartilaginous rings to prevent collapse.
• The trachea is lined with ciliated mucosa that helps move particles out of the airway.
• Larynx: Contains false and true vocal cords.
• Lungs:
  • Right lung: Superior, middle, and inferior lobes.
  • Left lung: Superior and inferior lobes (smaller due to space for the heart).

Bronchial Tree

• Primary Bronchi: Branch from the trachea into each lung.
• Further dividing into secondary and tertiary bronchi, leading into terminal bronchioles.
• Terminal Bronchioles: End of the conducting zone, leading to respiratory bronchioles where gas exchange begins.

Respiratory Zone Structure

• Alveoli: Main site for gas exchange, demonstrated by:
  • Presence of pulmonary capillaries closely surrounding alveoli.
  • Alveolar Ducts and Sacs: Structures leading to groups of alveoli.

Functions of the Conducting Zone

• Functions: Cleans, warms, and moistens the air.
• Changes occur in structure:
  • Cartilaginous rings decrease and are replaced with elastic fibers as passageways get smaller.
  • Initially ciliated epithelium becomes non-ciliated deeper in lungs, replaced by macrophages that can phagocytize particles.

Gas Exchange Process

• Gas exchange occurs across the respiratory membrane between alveoli and capillaries.
• Type I Alveolar Cells: Simple squamous epithelium facilitating gas exchange.
• Type II Alveolar Cells: Secrete surfactant to reduce surface tension and prevent alveolar collapse.

Importance of Surfactant

• Surfactant decreases surface tension, preventing the collapse of alveoli during breathing.
• Premature infants can suffer respiratory distress from lack of surfactant; surfactant therapy can be life-saving.

Alveolar Macrophages

• Present in alveolar spaces, protect against inhaled particles and pathogens.
• Vital in maintaining lung health and responding to infections.

Pressure Dynamics in the Thoracic Cavity

• Intrapulmonary Pressure: Pressure within the lungs (760 mmHg at sea level).
• Intrapleural Pressure: Pressure in the pleural cavity (slightly lower than intrapulmonary pressure).
• Maintaining pressure differential is crucial for lung inflation; equalization can lead to lung collapse.