Lec18 - Respiratory Systems.doc

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22 Apr 2012
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Respiratory Systems
1 partial pressure of gasses
Gasping is the most rudimentary method of obtaining air
Partial pressure of a gas
oThe pressure exerted by a given gas within a gas mixture
Composition of air
o79% nitrogen
o21% oxygen
o0.03% carbon dioxide
Humans breathe to get rid of co2, not to get oxygen
oOpposite for fish; breathe to get oxygen, not to expel co2
oAt least from a controls system point of view
Air pressure is going to be the sum of the partial pressures of the gases in the
atmosphere
2 partial pressure of gases
Norm-
oNormal levels
oOxia oxygen
oCapnia carbon dioxide
Hypo-
oDecreased levels
Hypoxaemia:
Decrease in blood (arterial) o2
Hyper-
oIncreased levels
3 air vs water
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Animals can breathe either water or air
Animals have a wide variety of respiratory organs
Air has 30x more oxygen than water
Oxygen diffuses 10000x faster in air than in water
Water breathers need to move more water over their gills than air breathers
need to move air over their lungs in order to extract the same amount of
oxygen
Water is 1000x more dense than air
Water is 50x more viscous than air
More energy is required to move water than air over a respiratory surface
oAs a result, the fish gill has become much more efficient at extracting
oxygen from water than a human lung does extracting oxygen from air
4 general forms of respiratory organs
Lungs for air breathing
oInternal
Gills for water breathing
oExternal
oInternal
Active vs passive ventilation (gills)
oActive
Muscle contraction
oPassive
Moving around in water
Tidal / unidirectional / non-directional ventilation
oTidal
Move air in and out through same passage (like tides of the
ocean)
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oUnidirectional
Fish gill
In through mouth, around, out the back
Bird lung
Different from mammals / amphibians / reptiles
oNon-directional
External gills passive ventilation in water
Diffusion lungs
oNot going to talking about this in detail
oCan be seen in spiders
Bimodal breathers (water/air; lungs/gills/skin)
oSome breathe both water and air; having multiple respiratory structures
5 external gills
Stick out from animal
Gas exchange across gills / tentacles
oOxygen diffuses across gills into blood
oGills are exposed to the bulk water and can be moved around (active
ventilation)
6 internal gills (aquatic invertebrates)
Most gills are found eternally
Encephalopod squid
oSpecialised mechanism of ventilation
oVentilation by muscular contraction not beating cilia
oWater sucked into the mantle and then forced out of a funnel
Source of propulsion force
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