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what is the Effect of Change in Lung Volume on Airway Resistance

  • As lung volume increases the alveolar septa will becomes stretched and will apply tension to airway walls
  • Will dilate airways and reduce resistance


Where is smooth muscle located in the respiratory tract?

  • Trachea- Trachealis m.
  • Bronchi and
  • bronchioles  


  1. what does the smooth muscle do in the respiratory tract?
  2. What happens when parasympathetic system is activated?
  3. sympathetic system?

  1. Regulates airway diameter
  2. Parasympathetic system – constrict
  3. Sympathetic system –  dilate 


what receptors are part of sympathetic system?

Beta 2


what are some inflammatory mediators that cause constriction to respiratory tract?

•Histamine and leukotrienes


what can dilate the airways?

  • Nonadrenergic noncholinergic pathway
  • Vagus;
  • Nitric oxide


  1. extrathoracic compression occurs during?
  2. give examples

  1. inspiration
  2. •Nares, pharynx, and larynx narrowing
    •Example - Laryngeal hemiplegia – “roaring” - horse;  inspiratory stridor – dog 


  1. when are intrathoracic structures compressed
  2. give an example


  1. during expiration
    • Intrapleural pressure exceeds airway lumen pressure
    • Cough – even greater pressure
  2. Example – tracheal collapse (toy dogs)


what is happening in A



  • a- normal
  • b- thickening of alveolar wall leads to low compliance
  • c- narrowing, leads to high resistance



  1. whats happening in A for slow breathing
  2. rapid

  1. normal filling during inspiration and release in expiration
  2. normal filling and release during rapid breathing


  1. What happens in B during slow breathing and rapid breathing

alveolus B with low lung compliance fills less


What happens in C

  • fills more slowly because its airway is partially obstructed
  • receive less ventilation and will be unevenly distributed


  1. Ideally - Ventilation and perfusion of the lung will......
  2. will there be gas exchange if alveoli are ventilated but not perfused?


  1. match
  2. No gas exchange


Causes of uneven distribution (4)

  1. Regional variations in lung inflation
  2. Regional variations in airway resistance
  3. Regional variations in lung compliance
  4. Collateral ventilation


what is this showing

Intrapleural pressure in dorsal part of chest will be more negative because of gravity


Explain this

(need to get better explination)

  • Compliance is different in different parts of the curve.  Change in volume with change in pressure.  When inspiration occurs, the change in pleural pressure will be the same in all of the regions, but because of the compliance difference, the change in V (volume) will be different in the different areas.  The larger the difference between dorsal and ventral chest- the more it will affect their ventilation. 


  1. which animals have complete connective tissue in secondary lobules
  2. partial
  3. none 

  1. Pigs and cattle – Complete
  2. Horse and sheep – Partial
  3. Dog and cat – None


what is collateral ventilation

•Movement of air between adjacent lobules when a main bronchus obstructed


  1. which animals have extensive collateral ventilation
  2. intermediate
  3. none

  1. Dog and cat – Extensive
  2. Horse and sheep - Intermediate
  3. Pig and cattle - None


  1. why do cows, sheep and pigs have extensive no collateral ventilation
  2. what happens if a bronchiole is blocked?

  1. one bronchiole is connected to one alveoli
  2. Air Cannot move from alveoli to alveoli 


  1. what animals have septa in lungs
  2. what do septa contain
  3. what can they do?

  1. cow, sheep and pigs

  2. connective tissue

  3. Septa allow infection to be walled off and deter spread


  1. why do dogs, cats and primates have extensive collateral ventilation
  2. what happens if a bronchiole is blocked
  3. what happens if they get an infection?

  1. bronchioles are connected
  2. If bronchioles are blocked off air can still go to other alveoli

  3. infection can spread easier because of no septa to wall off


  1. Explain the septa in horses
  2. why do they have intermediate collateral ventilation

  1. some septa are present
  2. not as extensive connections between bronchioles


how is pulmonary circulation different that systemic? (2 things)

  1. One organ must accommodate large variations in blood flow (cardiac output)
  2. Distribution of blood within the lung must match ventilation


  1. where are pulmonary capillaries located?
  2. are they all perfused at rest

  1. surround the alveolus and are exposed to pressure changes in the alveolus. 

  2. Not all 


  1. What is the pulmonary artery smooth muscle thickness in the pig/cow,
  2. horse,
  3. dog/sheep?

  1. Adult pig and cow – thick
  2. Horse – less
  3. Dog and sheep – least 


How does the animal increase and decrease blood flow resistance in the lungs to control the amount of blood flow?

  • Extra-alveolar vessels are affected by the volume of the lungs- if airways are stretched, the blood vessels are stretched which lead to a lower resistance to bloodflow


what is this diagram saying

  • Diagrammatic representation of the extra-alveolar vessels (pulmonary artery and vein) in the bronchovascular bundle and (inset) an enlargement of the alveolar vessels (capillaries) in the alveolar septum.
  • Notice that the alveolar septa are attached to the bronchovascular bundle so that they exert a radial traction on the bundle. 


  1. What are alveolar vessels?
  2. What type of pressure will affect these vessels? 
  3. What types of activities can cause a positive pressure in the alveolus?

  1. Thin capillaries surrounding the alveoli
  2. Pressure in the alveolus will affect these vessels;
  3. e.g. coughing,
    • straining or
    • mechanical ventilation will result in a positive pressure in the alveolus