PHIS 206 Lecture Notes - Lecture 17: Functional Residual Capacity, Smooth Muscle Tissue, Perfusion
Lecture 17: Gas Exchange
X-Ray
• Maximum volume of lungs at maximum inspiration (image a) → twice as much as min
volume
• Minimum volume of lungs at maximum expiration (image b)
Pressures of Breathing
• Note that transmural pressures are always positive (expiration passive here)
• If expiration becomes an active process, intrapleural may be higher than intra-alveolar
(blue>pink) which means transmural pressure goes negative → collapse
• Diagram
• When you breathe in, you lower the pressure in your lungs
• When you breathe out, you increase the pressure in your lungs (pushes out the air)
Surfactant
• Surfactant aids in the inflation of the alveoli
• Like balloons, alveoli are most difficult to inflate when they are small
• Surfactant enables small and large alveoli to stay open at the same time
• The larger alveoli are easier to blow up than the small alveoli (like balloons) (if surfactant
didn’t exist)
Spirometry
• Before inspiration → FRC (functional residual capacity)
• After Expiration → FRC
• Normal Breath → TV
• After Inspiration, Before Expiration → FRC + TV → will be question
Vocabulary
• Ventilation (V) → fill (and empty) lung passages and alveoli with air
• Perfusion (Q) → Send blood to capillaries within regions of the lung
• There are mechanisms for matching the ventilation and the perfusion for the sake of
efficiency
• The “match” isn’t perfect → for the lungs as a whole, V/Q = 0.8
• V/Q can change depending upon the primary fuel source
• Ratio is different in different parts of the lung
• Understand vocab
Dead Space
• Portion of the respiratory system where exchange doesn’t happen → “dead space”
• Corresponds to areas that are ventilated, but not perfused
• Air here is “in the way”
• Snorkel idea
• Air in conducting zone doesn’t get used
• Some fresh air gets stuck in dead space, can’t use all the air we breathe in
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Document Summary
X-ray: maximum volume of lungs at maximum inspiration (image a) twice as much as min volume, minimum volume of lungs at maximum expiration (image b) Pressures of breathing: note that transmural pressures are always positive (expiration passive here) Spirometry: before inspiration frc (functional residual capacity, after expiration frc, normal breath tv, after inspiration, before expiration frc + tv will be question. In most of the body, when a region is oxygen deprived, it receives more blood. In the lung, it is the opposite reduces waste of ventilation: no one is sure how this works yet. Composition of air: total atmospheric pressure, n2 = 79, o2 = 21, other components, carbon dioxide, argon, helium, air serves as the source for o2 and the sink for co2 in our external respiration. Exchange: diffusion, all transport/flow of o2 and co2 is driven by the difference in partial pressures.