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GAS EXCHANGE & CIRCULATION
CHAPTER 42 (867–891)
MOVEMENT OF GASES
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Both O2 and CO2 move by _____________________________________________________
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The movement down a _____________________________________________________
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If a gas produced in one location, it diffuses away
But diffusion is usually not _________________________ or __________________________
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Time it takes a substance to diffuse is proportional to the square of the distance
o If it takes ________________ to diffuse 100µm
o It will take ________________ to diffuse 1mm
o It would take ________________ to diffuse 1cm!
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Therefore 1 mm – the maximum _______________________________ distance for simple
diffusion to supply cells with oxygen
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Poses a problem if cells are _______________________ from an O2 source
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They will asphyxiate!
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So animals are limited to being 2mm thin
But most animals are thicker than 2 mm!
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A _______________________________ mechanism must be involved to ensure no cell is >1
mm from O2
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More later …
REQUIREMENTS FOR GAS EXCHANGE
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In order to facilitate gas exchange certain requirements must be met:
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_______________________________ – gas dissolves into the water film and diffuses
across cell membranes
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Adequate respiratory _______________________________ to supply internal tissues
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Larger animals have more _______________________________
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More cells equals a _______________________________
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GAS EXCHANGE
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____________________ large organisms still use _______________________________ – across
moist surfaces
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If the animal is too large for diffusion ______________________________________________
they add a ______________________________________________________________
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Sites of gas exchange are highly _______________________________
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Capillaries pick-up and carry ______________ to the tissues in exchange for _____________
OPTIONS FOR GAS EXCHANGE
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All animals need a way to facilitate exchange
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There are two major strategies
1. Exchange gases over their _______________________________
2. Exchange gases at _______________________________
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_______________________________
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_______________________________
CUTANEOUS RESPIRATION
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The diffusion of gases across the body surfaces
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When does this work?
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Animals dependent on water – ___________________________________________________
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Animals with thin skin – ________________________________________________________
Poriferans – sponges
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Water canals everywhere
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All cells are directly _______________________________
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Choanocytes generate a constant current
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Immediate _______________________________
_______________________________ for gas exchange
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Cnidarians
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Some can get very large – how?
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Only 2 tissue layers (just _______________________________)
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The ‘bulk’ of big jellyfish is non-living jelly – _______________________________
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Gastrovascular cavity supplies O2 to the _______________________________
Flatworms – are flat!
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Not many platyhelminths get thicker than _______________________________
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Earthworm gas exchange
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Live in terrestrial but _______________________________ to help keep the body surface moist
(facilitates exchange)
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Numerous _______________________________ just beneath the integument which
_______________________________
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Works the same way as our lungs!
What about more complex animals?
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Not just restricted to the simpler animals
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Largely dependent on the animal’s
Usually found in
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Animals that are ______________________________________________________________
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Animals that still ______________________________________________________________
GILL BREATHING
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Most large aquatic organisms rely on _______________________________
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__________________________________________________ (outgrowths) of the body surface
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Thin-walled structures (_______________________________)
Why not cutaneous respiration?
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Many are covered with protective _______________________________
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__________________________________________
Not enough _______________________________ to supply all cells
Gills can be outside the body (_______________________________) or protected inside a
chamber (_______________________________)
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Evolutionary trend in gills is towards either
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An increased _______________________________
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Increased _______________________________
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Both lead to _______________________________ gas exchange
Many annelids (the Polychaetes) have large and elaborate lateral appendages
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_______________________________
Multitasking structures
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_______________________________
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_______________________________
_______________________________ – 1 pair/segment
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Relatively _______________________________
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Rich _______________________________
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Other polychaete worms have highly modified appendages - _______________________________
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Large feathery structures on the anterior end
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A massive, highly vascularized _______________________________
Multitasking again!
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_______________________________
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_______________________________
VENTILATION
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Internal gills pose a problem
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How do you get water to ________________________________________________________
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Ventilation
Fish – open their mouths & opercula to generate _____________________________
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Or they don’t ______________________________________________________
Lobsters, crabs, shrimp – beat appendages (_______________________________) to create water
currents
COUNTERCURRENT EXCHANGE
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The most efficient way to collect O2 out of water
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Water moves in the _______________________________ direction as the blood
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There is always a _______________________________ drawing O2 into the blood
AIR BREATHING
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Turn your gills inside out
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Rather than outpocketings, use _______________________________ or infoldings
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Forming a lung – an internal chamber
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Still has to be ________________________ with a large _______________________________
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But there are problems with this system
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Every breath you take, _______________________________
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More surface area equals more water loss
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Lungs vary in their efficiency
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Frogs have small lungs
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Smaller surface area for gas exchange _______________________________
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Why?
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_______________________________ (skin) is their major gas exchange structure
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Therefore they need to keep moist
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Stay near water
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Mucus (helps for sunburn too)
OTHER VERTEBRATE LUNGS
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Thousands of alveoli – _______________________________
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The site of _______________________________
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Associated with blood vessels – _______________________________
Incredibly large surface area _______________________________ in humans
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Ciliated & mucus lining
AIR BREATHING
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Insects use an entirely different system – the _______________________________
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Open to the environment through multiple _______________________________
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The network of tracheae and tracheoles (small airways) reaches nearly
______________________________________________________________
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Based on simple _______________________________ with each cell having a
_______________________________
CIRCULATORY SYSTEMS
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So you’ve exchanged your gases, now what?
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You need a way to get the O2 to the tissues and cells
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You need a circulatory system
Circulatory systems come in three different flavours:
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_______________________________ cavity
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_______________________________ system
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_______________________________ system
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GASTROVASCULAR CAVITY
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Think of who has a GVC?
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What are their body shapes?
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_______________________________
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_______________________________, but some are quite large >>2mm
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Diffusion cannot get into the deeper layers
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Does it need to?
_______________________________
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_______________________________, thin & flat
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Diffusion is an efficient mechanism to get to all tissues
The GVC works to move gasses and nutrients
CIRCULATORY SYSTEMS
Open Circulatory System
Closed Circulatory System
OPEN CIRCULATORY SYSTEMS
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The _______________________________ pumps the circulatory fluid throughout the system
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Vessels usually leave the heart and are _______________________________
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Fluid spills out into cavities called _______________________________
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Fluid then _______________________________ the cells providing nutrients, O2
Fluid re-enters the heart through ____________________________ (_______________________)
or separate vessels
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The body fluid that bathes the tissues is the ________________________ as that inside the vessels
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No _______________________________
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Just _______________________________
CLOSED CIRCULATORY SYSTEMS
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The ______________________________ pumps the circulatory fluid throughout the entire system
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The circuit is _______________________________ enclosed in a series of blood vessels
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Two _______________________________ types of fluid in the body are required
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The _______________________________ within the vessels
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And _______________________________ which bathes the cells in the tissues
Seen in:
– Some annelids (earthworms)
– Active molluscs – squid & octopi
– The vertebrates
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EARTHWORM CIRCULATION
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Advantages of a closed system
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Higher _______________________________
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Greater _______________________________
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More efficient _______________________________
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_______________________________ carries blood towards the heart – anteriorly
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_______________________________ carry blood towards the tissues – posteriorly
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5 pairs of auxiliary hearts (pseudohearts) come off the main dorsal heart and connect the vessels
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_______________________________ (arterioles)
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Carry blood towards the heart
_______________________________
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Carry blood away from the heart
_______________________________ (venules)
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VERTEBRATE CIRCULATORY VESSELS
Link arterioles with venules
_______________________________
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Carry blood between capillary beds
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All are modifications of a similar structure depending blood pressure
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Arteries (arterioles)
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Usually very _____________________________ made mostly of muscle and connective tissue
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Necessary to resist the enormous _______________________________
Veins (venules)
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Relatively _______________________________ -walled vessels containing
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Blood pressure is relatively _______________________________
Capillaries
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Very thin walled vessels
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One cell thick
Site of _______________________________
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ARTERIES AND VEINS
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Muscular walls of arteries are _______________________________
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Assists blood movement to the _______________________________
Veins have _______________________________ muscle to effectively move blood
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Rely upon contraction of nearby _______________________________
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Valves prevent _______________________________ since the pressure is so low
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Think about when you sit still for a long time
CAPILLARIES
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Extremely thin-walled with only one cell layer
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Huge number and total surface area to reduced _________________ and _____________________
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What other benefit does this have?
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More efficient _______________________________
VERTEBRATE CIRCULATORY SYSTEMS
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Evolution of the vertebrates lead to an increase in complexity of the circulatory system
Fish
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A simple _______________________________ heart
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One atrium – from body
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One ventricle – to body
One circulatory loop
1. Heart (Ventricle)
2. Arteries
3. Gill capillaries
4. Portal veins
5. Systemic capillaries
6. Veins
7. Heart (Atrium)
Amphibians
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A 2nd circulatory loop exists – _______________________________
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Heart divided into _______________________________ as a result
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Two atria
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One ventricle – some _______________________________
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Ridges in the ventricle wall prevent
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Pulmocutaneous circuit
1. ‘Right’ ventricle
2. Arteries
3. Lung and skin capillaries
4. Veins
5. Left atrium
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Systemic circuit
6. ‘Left’ ventricle
7. Arteries
8. Systemic capillaries
9. Veins
10. Right atrium
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Advantage is _______________________________ to the organs because of a
_______________________________ heart beat
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More efficient gas exchange at tissues
Reptiles
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Also have a 3 chamber heart with 2 blood circuits –
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Pulmonary circuit
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circulation
_______________________________ is not used as a respiratory surface
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Systemic circuit
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Ventricle has a _______________________________ to minimize mixing of blood
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Increased efficiency – more _______________________________
Birds and Mammals
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Also have double circulation
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Pulmonary circuit
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Systemic circuit
A _______________________________ divides the ventricle into two
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No mixing of oxygen-rich and oxygen-poor blood
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TAKEN TOGETHER
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Gas exchange and circulation
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Both O2 and CO2 move by diffusion
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Inhaled air
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[O2] = 104
[CO2] = 40
[O2] = <40
[CO2] = >45
Deoxygenated blood
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[CO2] = 0.2
At cells
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[O2] = 160
Oxygenated blood
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Down their concentration (pressure) gradients
[O2] = 40
[CO2] = 45
Exhaled air
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[O2] = 120
[CO2] = 27
FIGURES USED
42.19
42.1
42.23
33.4
33.10
42.20
42.21
42.22
42.2
33.10
42.3
42.10
42.9
42.11
42.4
42.27