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Lecture 7

BIO271H1 Lecture Notes - Lecture 7: Internal Intercostal Muscles, Negative Feedback, Paracrine Signalling

Course Code
Chris Garside

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Lecture 7 (March 9, 2016): Respiratory Systems
Ventilation and Gas Exchange in Air
Respiratory organs are typically thin with a large SA and must be kept moist
Two animal lineages that colonized terrestrial habitats
System is almost identical to their water-breathing cousins
Air moves through bronchial chamber
Chelicerates (arachnids)
Book lung
Simple tracheal system
Extensive, branched tracheal system where air filled tubes are open
to the outside via spiracles
Tracheae branch to form tracheoles (end of the tube and filled
with hemolymph, so most gases dissolve in it)
Very extensively branched and high SA
Diffusion distance is very short
Tracheole is invaginated into the muscle tissue in the myofibers
Oxygen has a high diffusion coefficient in air
Contraction of abdominal muscles or movements of
the thorax
oAir flows in and out of the same
oEnter anterior spiracles and exit
abdominal spiracles
Ram ventilation (draft ventilation)
They leave some of their spiracles open
which forces the air through while they are
oDiscontinuous gas exchange
Phase 1 (spiracles are closed)
No gas exchange
PO2 decreases
oThis part triggers phase 2
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CO2 is being produced, but it can be
converted into bicarbonate and stored in the
hemolymph of the tracheoles
Total pressure in trachea decreases
Phase 2 (spiracles flutter open and close in rapid
Since there is lower pressure inside the
trachea, air will move inside
Little bursts of release of CO2 down the
pressure gradient
Phase 3
Triggered by an increase of partial pressure
of CO2
Bicarbonate can no longer be store so CO2
builds up
Then total pressure in trachea increases
Spiracles open and CO2 is released
More oxygen will flow in down its partial
pressure gradient
Why do insects do this discontinuous gas exchange?
To decrease desiccation maybe
Or to maintain the partial pressure gradient
Or to reduce the effects of oxygen (which is
a toxic molecule
Do insects breathe like humans?
oWhen they looked inside, they saw expanded and collapsed
trachea in insects, but they could not correlate that with any
movement of fluids or musculature in the body, so
somehow they are able to change the pressure in their body
and move air in and out
oInsects probably have lots of other mechanisms
Many insects have secondarily moves back into aquatic habitats
oTrachea are very inefficient for ventilation in water
Too expensive
oOne strategy is to use cutaneous respiration and they can
survive with just the diffusion across the surface
oBut the larger insects who live in low oxygenated areas
need other strategies
Tracheal gills
Fan-shaped structure
Insects constantly move the gills around to
get fresh water
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Very thin cuticle over the gills reducing
diffusion distance
oThey can still use air to breathe
Siphons can lead up to the surface of the water to
get the air
Adapted wings, legs, or specialized hair to carry
bubbles of air into the water with them
Functions as a short-term physical gill
Bubbles will shrink in size eventually, so
they do have to come back to the surface to
get another air bubble
Clicker Question: In teleost fish, water enters the mouth when the buccal cavity expands
Air breathing has evolved a lot
Gills are thin, but reinforced
Highly vascularized respiratory structures
Catfish has vascularized stomach
Some fish have specialized pockets of the gut which are highly
Eels have vascularized mouth and pharyngeal activity
Lung fish
oComplex lungs
oHigh SA
oTwo circuit circulatory system
Ventilation is tidal (but unidirectional in water breathing fish)
oUses buccal force pump to create pressure to push the
fluids across the respiratory surface
oMouth opens, buccal activity expands, decrease in pressure,
air move into the buccal activity, mouth closes, buccal
cavity compresses, air moves into anterior chamber and
stores in there. Posterior chamber compresses moving spent
air out, then buccal cavity compresses pushes air from the
anterior chamber into the posterior chamber so gas
exchange can occur
oMost fish live in habitats that do get hypoxic
oMost of the these fish have gills which supplements the gas
Cutaneous respiration
External gills
Simple bilobed lungs
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