Respiration 1

• Main functions of the respiratory system

  • Transport of oxygen and carbon dioxide between the tissues and environment
• Components of the respiratory system

  • Nose
  • Nasal cavity
  • Paranasal sinuses
  • Pharynx
  • Larynx
  • Trachea
  • Bronchi and bronchioles
  • Lungs and alveoli

  
• Type I alveolar cells


  Predominant, simple squamous epithelium, main site of gas exchange

  
• Type II alveolar cells


  Cuboidal epithelial cells containing microvilli, secrete fluid containing surfactant
• Lung compliance


  Distensibility of the lungs. High lung compliance means the lungs will expand easily. Compliance is decreased in pulmonary edema, insufficient surfactant, and scar tissue.

  
• Elastic recoil


  Lung's intrinsic tendency to deflate following inflation (inspiration), due to pulmonary elastic fibres and surface tension
• Pulmonary surfactant


  Lipoprotein complex (70% lipid, mainly dipalmitoylphosphatidylcholine; 30% protein) produced by Type II alveolar epithelial cells, lowers surface tension so breathing can occur without too much effort, increases lung compliance and reduces the tendency of the lungs to recoil inward, makes the alveoli stable against collapse

  
• As alveoli radii change

  Surface tension varies. At end of expiration, alveoli radii reduced, surfactant more compressed and more active, reducing surface tension. At end of inspiration, alveoli expanded, surfactant more diluted and less active, increasing surface tension.

  
• Panting


  A controlled increase in respiratory frequency accompanied by a decrease in tidal volume, to increase ventilation of the upper respiratory tract, preserve alveolar ventilation and increase evaporative heat loss

  
• Inspiration


  Active process, air moves into the lungs due to a decrease in air pressure within the lungs

  
• Normal expiration


  Passive process, air moves out of the lungs due to an increase in air pressure within the lungs

  
• Forceful exhalation


  The abdominal and internal intercostals muscles contract

  
• Intrapulmonary/alveolar pressure


  The pressure of the air within the alveoli, changes during breathing, eventually equalizes with atmospheric pressure

  
• Intrapleural/pleural pressure


  The pressure of the air within the pleural cavity, between the visceral and parietal pleurae, changes during breathing, is always lower than or negative to the intrapulmonary pressure

  
• Transpulmonary pressure


  Represents the pressure that effectively promotes air flow and distends the lungs, the difference between the intrapleural pressure and the intrapulmonary pressure

  
• Intrapleural pressure is normally negative


  Due to inward lung and outward chest wall recoil

  
• In pneumothorax


  Air enters the pleural space, intrapleural pressure increases and lung volume decreases, can cause partial or complete lung collapse