Biology 2601A/B Lecture Notes - Lecture 12: Partial Pressure, Exhalation, Thoracic Cavity

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We’ll fous o soe of the was Natural Selection has worked to improve the O2 extraction efficiency of
animals (especially in water).
Tidal Ventilation - Mammals
- Tidal Ventilation: pathway to get air in and out of internal environment is the same
- Diaphragm moves downwards (contracts) to expand the volume of the thoracic cavity. This increase in
volume causes a lower pressure inside the thoracic cavity than outside so air is sucked in. Inhalation is
an active process.
- Diaphragm relaxes which decreases volume of thoracic cavity which causes a higher pressure inside
than outside, so air is pushed out. Exhalation is a passive process.
Tidal Ventilation is negative pressure! Mammals usually use positive pressure to move liquids around the
body (heart pumps blood through circulatory system), but we use negative pressure to move air in.
Gas Exchange
1. Cocurrent/Concurrent Gas Exchange Water Breathers
- medium and blood flow in same direction
- found in VERY FEW gill types
- 50-50 euiliatio at est…
- at equilibrium, there is no longer a P of O2
btwn. the medium and blood, so no further
diffusion occurs.
- Air comes into and out of the alveoli, where gas exchange
happens, in a tidal fashion it takes the same route in and out.
The partial pressure of air that reaches the alveoli is only 100
compared to the partial pressure of air outside of 159. This is
eause whe we eath, we do’t ehage the etie
volume of our lungs some stale air is taken in as well, which
dilutes the pressure of air that comes in.
How do medium and blood flow relative to each other?
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