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Lecture 14

BIOL 2P97 Lecture Notes - Lecture 14: Breathing, Bronchus, Bronchiole

Biological Sciences
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-dened as bulk ow of air from the atmosphere to the alveoli
-respiratory cycle: inspiration followed by an expiration
Lung volumes during ventilation Fig 17.7 b)
1. Tidal volume: Air that moves with normal inspiration/expiration (500mL per
breath for normal person)
2. Inspiratory reserve volume: additional volume that could be breathed in (extra
3. Expiratory reserve volume: air that could be forcefully exhaled after a normal
4. Residual volume: volume left in the respiratory system after maximum exhalation
Lung Capacities: The sum of 2 or more volumes
Total lung capacity: sum of all volumes
Inspiratory capacity: tidal volume + inspiratory reserve volume
Vital capacity: tidal volume + inspiratory reserve volume +expiratory reserve
volume (NO RESIDUAL VOLUME) ** MC question
Mechanics of Breathing
How does air move into our lungs?  Pressure gradients
Basic Principles
[Look at textbook for breathing/lung pictures]
-air always travels from an area of high pressure to low pressure
-as volume increases, pressure decreases (Boyle’s Law)
We need to keep in mind
-atmospheric pressure
-intrapulmonary pressure and volume (pressure in the lungs)
-intrathoracic pressure and volume (across entire thorax)
-intrapleural pressure (seen as negative pressure(not a true negative-can’t have
that) – less than the atmosphere)
Negative Pleural Pressure – opposing forces
-elastic recoil of lungs (pulling the lungs inwards)
-the thoracic wall wants to expand (maintains rigid structure – pulls thoracic wall
-thus pleura is pulled in opposite directions
-intrapleural space = resulting in negative pressure
-pleura “pushed” to thoracic wall
Why don’t the opposing forces pull the visceral and parietal pleura apart?
Bc of Pleural Fluid
-contains water
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