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