5. Respiration- The Exchange of Gases
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Transcript of 5. Respiration- The Exchange of Gases
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Respiration:
The Exchange of Gases
Respiration (gas exchange): the interchangebetween an animal and its environment.
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Mechanisms of Gas Exchange
Three phases of gas exchange:
1) Breathing
- gas exchange with environment
2) Gas transport
- circulatory system
- blood vessels
3) Servicing body tissues
- gas exchange with tissues
- O2 uptake - cellular respiration
- CO2 release - waste product
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Mechanisms of Gas Exchange
Respiratory surface - the part of the animal where O2 diffuses
into the animal and CO2 diffuses out to
the environment.
- covered by living cells (single layer, moist)
Outer skin
- skin breathers
- capillaries below skin-small, long, flat organisms
-high surface to volume ratio
e. g. earthworm and hydra
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Mechanisms of Gas Exchange
Most animals require specific adaptations for gas exchange
Gills
- feather-like extensions body surface
- very high surface area- in contact with environment
- must always be moist!!
e.g. fish, amphibians, crabs and
mollusca
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Mechanisms of Gas Exchange
In most terrestrial organisms, the respiratory surfaces areFolded into the body.
Tracheal system
- extensive system of internal tubes
- exchange gases with the cells
- no assistance from the circulatory
system.
e. g. insects
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Mechanisms of Gas Exchange
Most terrestrial organisms have lungs
Lungs
- internal sacs lined with moist
epithelium
- inner surfaces branch extensively
- large surface area!!
- gases carried between lungs and
body cells by the circulation.
e.g. amphibians, reptiles, birds and
mammals.
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Fish Gills
Gills are adapted for gas exchange in aquatic environments
Water - low dissolved O2
Ventilation- mechanism to increase
contact between respiratory
surface (gills or lungs)
and the environment.
- fish ventilate their gills
to maintain the flow of
O2 rich water.
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Fish Gills
Countercurrent flow in gills enhances O2 transfer
Countercurrent exchange
- the transfer of something from a
fluid moving in one direction to
another fluid moving in the
opposite direction.
- opposite flows maintain a diffusion
gradient.
Gills
- water (O2-rich) flows one way
- blood (O2-poor) flows the other way
* can remove 80% of water O2
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Tracheal System
Insect tracheae are tubes that branch throughout the body
air sacs - contraction of muscles around them control air movement
tracheoles - narrowest tubes that extend to the cells; contain fluid
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Lungs - terrestrial vertebrates
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Lungs
The alveoli are the site of gas exchange with the circulation.
Alveoli
- tiny sacs lined with a thin layer
of epithelial cells; the exchange
surface with blood
- each lung contains millions
- O2 dissolves in the film of
moisture lining the epithelialcells and diffuses across to the
blood
- CO2 moves the opposite way
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Lungs - BreathingBreathing - the alternation of inhalation and exhalation.
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Lungs - Breathing
Breathing in birds involves a one-way flow of air rather than
an in-and-out flow in humans.
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Control of Breathing
Breathing is automatically controlled
Breathing control centers
- in brain (pons and medulla)
- nerves from medulla signal diaphragmand rib muscles to contract (inhale)
- pons smooths out rhythm of breathing.
- pH sensing - control of CO2 release
- decrease in pH causes an increase
in breathing rate.
Hyperventilation - deep, rapid breathing.
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Gas TransportBlood transports the respiratory gases
Heart has two divisions:
1) left side handles O2-rich blood from
the lungs (pumps blood to body)
2) right side handles O2-poor blood
from the rest of the body
- pumps blood to alveolar capillaries
(gas exchange)
Partial pressure
- the portion of a mixed gas that a
particular pure gas accounts for
- gradients determine movement
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Gas Transport
Hemoglobin - the molecule in red blood cells that carries O2
- four polypeptide chains and a heme group
containing iron
- can carry up to 4 molecules of O2
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Gas TransportHemoglobin helps transport CO2 and buffer the blood
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Gas TransportThe human fetus exchanges gases with the mothers bloodstream
Fetus
- lungs are full of fluid and
non-functional
- capillaries from the umbilical
cord fan out into the placenta
- gas exchange occurs with the
maternal blood in the placenta
- countercurrent exchange offetal and maternal blood
- fetal hemoglobin has a higher
affinity for O2.
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SUMMARY
- Mechanisms of gas exchange
(skin, gills, tracheal system, lungs)
- Breathing in water
- countercurrent exchange
- Breathing in air
- tracheal system (insects)
- lungs (humans)
- Breathing (control by brain)
- Gas transport (circulation, blood, hemoglobin)