Respiratory

• Mechanics of pulmonary ventilation

  Movement of air into/out of the lungs
• Gas exchange in lungs and tissues

  Exchange of oxygen and carbon dioxide between blood and alveoli, and between blood and tissues
• Transport of O2 and CO2

  Transport of oxygen and carbon dioxide between the lungs and the tissues
• Regulation of breathing


  Mechanisms that control and adjust the rate and depth of breathing

  
• Processes of respiration

  • Ventilation - movement of air into/out of the lungs
  • Gas exchange between blood and alveoli, and between blood and tissues
  • Transport of gases between the lungs and the tissues
  • Cellular respiration
• Respiratory system functions

  • Gas exchange
  • Acid-base balance
  • Water and heat balance
  • Protective
  • Filter of blood
  • Regulatory
• Pleura and pleural cavity


  Membranes and space surrounding the lungs
• Pulmonary circulation

  Blood flow through the lungs
• Airway functions

  • Filter/cleaning/warming
  • Resonating chamber for speech
  • Olfaction
• Pulmonary defence mechanisms

  • Role of mucous secretions and cilia: trap & remove inspired particles
  • Role of smooth muscles: adjust airway diameter to control airflow resistance & ventilation distribution
• Air reaching the bronchi is warmed, cleansed & saturated with water vapors
• Ciliated respiratory epithelium

  Lining of the trachea, bronchi, and lung parenchyma
• Airway divisions

  • Conducting Zone (air flow)
  • Respiratory Zone (gas exchange)
• Alveolar cells

  Two types: type I and type II
• Air-blood barrier

  Thin membrane across which gas exchange occurs
• Pulmonary ventilation

  1. Inspiration - air flows into the lungs

  2. Expiration - gases exit the lungs
• Mechanics of ventilation

  • Volume changes => Pressure changes => Flow of gases to equalize pressure
• Boyle's law

  Pressure of a gas is inversely proportional to the volume
• Inspiration


  • Active process requiring skeletal muscle contraction
• Inspiratory muscles (quiet breathing)

  • Diaphragm
  • External intercostal muscles
• Expiration

  • Passive during quiet, normal breathing
  • Active (forced) using internal intercostals & abdominal muscles
• Pressure gradient and airway resistance


  Determine air flow: F = ΔP/R
• Intrapulmonary (alveolar) pressure (PA)

  Pressure within the alveoli, rises and falls during breathing
• Intrapleural pressure (Ppl)

  Pressure within the pleural cavity, negative relative to atmospheric pressure
• Transpulmonary pressure

  Difference between alveolar pressure (PA) and intrapleural pressure (Ppl)
• Pneumothorax causes the lung to collapse due to Ppl = Patm
• Lung elasticity and surface tension

  Forces promoting lung collapse, opposed by chest wall elasticity
• Compliance


  Measure of how easily the lungs can be stretched, reciprocal of elastance
• Decreased lung compliance


  Lesser increase in lung volume for any given increase in transpulmonary pressure
• Factors decreasing lung compliance

  • Scar tissue or fibrosis
  • Decreased surfactant production
  • Decreased thoracic cage expansibility
  • Lung diseases (fibrosis, pneumonia, edema)
  • Airway blockage (mucus/fluid)
• Surface tension


  Cohesive forces between molecules at the air-liquid interface in the alveoli
• Pulmonary surfactant

  Mixture of lipids and proteins secreted by type II alveolar cells, lowers surface tension and stabilizes alveoli
• Role of surfactant

  • Lowers surface tension to improve lung compliance and decrease work of breathing
  • Stabilizes alveoli to prevent collapse
  • Reduces pulmonary edema
• Surfactant


  • Mixture of lipids and proteins secreted by type 2 alveolar cells
  • Lines the alveolar surface and decreases surface tension, preventing alveolar collapse
  • Acts like a detergent
• Type II granular pneumocytes


  Surfactant producing cells in the alveolar walls
• Composition of pulmonary surfactant

  • Phospholipids
  • Proteins
• Surfactant molecules

  Arranged on an air-water interface, disrupting the cohesive forces between water molecules
• Role of surfactant

  1. Lowers surface tension, making inflation of alveoli easier and decreasing work of breathing

  2. Stabilizes alveoli, preventing collapse

  3. Reduces pulmonary capillary filtration, helping to prevent pulmonary edema
• Schematic diagram of the alveoli and a terminal airway shows the liquid coating on the alveolar surface acting to reduce the size of the alveoli
• Secretion of surfactant occurs via exocytosis of the lamellar body