External respiration

• External respiration:

  Oxygen diffuses from alveoli into pulmonary cpaillaroes. Carbon dioxide moves in the opposite direction
• What is gas exchange?

  Gases move from the alveolar air and blood by passive diffusion
• what is the contact time?

  0.75 with alveoli and reaches equilibrium in about 0.25 seconds
• What occurs to diffusion rate with excerise?

  heart rate increases so blood flow increases so time for diffusion decreases
• why might we run out of oxygen during heavy exercise?

  As blood flow increases less time for oxygen diffusion, so less oxygen in blood
• what is partial pressure?


  individual gas pressure it exerts
• How to work out partial pressure?

  total pressure X percentage it occupies
• what is the composition of air?

  • 78.09% nitrogen PP=593.5mmHg
  • 20.95% oxygen PP=159.2mmHg
  • 0.93% argon (& other inert gases)
  • 0.03% carbon dioxide PP= 0.23mmHg
• what is pressure at sea level?

  760 mmHg
• what is the limiting factor of breathing at sea level?

  Co2 levels
• what is the limiting factor at altitude?

  Oxygen levels
• what occurs if you live at high altitudes all your life?


  they have a barrel chest
• what occurs with COPD?

  barrel chest
• what is the respiratory membrane?

  alveolar walls and blood vessel walls
• Describe alveolus:

  • elastic fibres for movement and stretch
  • macrophage (dust cells) for filtration
  • 2 types of alveolar cell (pulmonary epithelial cells)
• what happens to dust cells in smokers?

  Smoke particles collects into dust cells
• Which type of alveoli cell releases surfactant?

  type 2
• what is the surfactant like?

  lipid-rich
• what does surfactant do?

  lowers surface tenstion

  Increases in surface area
• when is surfactant produced in prenatal?

  from week 26
• how to treat respiratory distress syndrome?

  cortisol treatment in mother
• What makes up the respiratory membrane structure?

  • Type 1 alveolar cells
  • Alveolar basement membrane
  • Interstitial space: elastic fibres
  • Capillary basement membrane
  • Capillary endothelium
• what affects gas exchange?

  • surface are
  • diffusionn distance
  • diffusion gradient

  ANY THING THAT AFFECTS FICKS LAW
• what increases surface area?

  inflation

  mutliple small alveoli increase surface are
• what do healthy alveoli look like?

  spherical structure that have a 80-100 square meters
• diffusion distance increases with fluid and mucus in the lungs
• Rate of diffusion is explained by Fick’s law and means that diffusion of gas is slow if the diffusion thickness increases
• how do gases move?

  from high to low PP
• when is repeated replenishment increased?

  with high PO2 and low Co2
• what is ventilation?


  Amount of air reaching the alveoli per min
• how do ventilation and perfusion related?

  The rate of oxygen uptake depends on the rate at which it is supplied (ventilation), and the rate at which it is removed (perfusion).
• what is perfusion?


  amount of blood reaching the alveolid per min
• what does a mismatch of V/P (V/Q) lead to ?

  respiratory failure
• how to detect embolism?

  V/P (V/Q) scan
• where might you find a V/Q ratio mismatch?

  top of lungs (lots of air - dead space)
• what occurs more at bottom of lungs?

  more diffusion
• What occurs at the apex of the lungs?

  Higher V/Q ratio, there more ventilation
• what occurs when V/Q = infinity?

  no perfusion
• what does a high V/Q mean?

  more ventialtion
• what does V/Q =0 mean?

  Perfusion but no ventilation