Respiratory System 2

• Law of LaPlace


  P=2T/r (P=Pressure, T=Surface Tension, r=radius)
• Surfactant


  A surface active agent in water, greatly reduces the surface tension of water
• Surfactant formation


  Formed in lamellar bodies in type 2 alveolar cells
• Tubular myelin secretion


  1. Secreted by exocytosis

  2. Regulated by increase tidal volumes
• Surface tension


  • Minimises the area of contact with the air
  • Pressure is equalised in the large/small alveoli
• Roles of Surfactant


  • Reduces work in inspiration à increased compliance
  • Stabilizes alveoli
  • Reduces alveolar tension and keeps them dry à prevents pulmonary oedema
  • Important for lung expansion at birth
• Respiratory rate


  Number of breaths per minute
• Minute ventilation


  Amount of air moved into and out of respiratory system per minute
• Anatomic dead space (ADS)


  Part of respiratory system where gas exchange does not take place (Conducting Zone~150mls)
• Normal respiratory values


  • Tidal Volume (TV) ~ 500 mls
  • Respiratory Rate ~ 12 breaths per minute
  • Minute ventilation average (MV) ~ 6 L/min
  • Anatomical dead space ~150mls (AV 350mls/breath)
• Alveolar ventilation


  Changed by taking deeper breaths and reducing dead space
• Partial pressure


  The pressure exerted by each gas in a mixture
• Dalton's law


  Total pressure = sum of partial pressure
• Atmospheric air is mostly nitrogen and oxygen
• Partial pressure


  Changes with atmospheric pressure/altitude
• Fick's Law


  Diffusion coefficient of gases in water
• A limitation of gas movement is the rate at which these gases diffuse through tissue water
• Respiratory membrane composition


  • Layer of fluid lining the alveolus, containing surfactant
  • Alveolar epithelium
  • Epithelial basement membrane
  • Capillary basement membrane
  • Capillary endothelium
• The average diameter of pulmonary capillaries is 5 micrometres
• Distance between alveolar space and capillary lumen is 1-2micrometres