1 lecture #10 – animal circulation and gas exchange systems
TRANSCRIPT
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Lecture #10 – Animal Circulation and Gas Exchange Systems
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Key Concepts:
• Circulation and gas exchange – why?• Circulation – spanning diversity• Hearts – the evolution of double circulation• Blood circulation and capillary exchange• Blood structure and function• Gas exchange – spanning diversity• Breathing – spanning diversity• Respiratory pigments
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Animals use O2 and produce CO2
• All animals are aerobicLots of oxygen is required to support active
mobilitySome animals use lots of oxygen to maintain
body temperature• All animals produce CO2 as a byproduct of
aerobic respiration• Gasses must be exchanged
Oxygen must be acquired from the environmentCarbon dioxide must be released to the
environment
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Except……breaking news!http://www.biomedcentral.com/1741-7007/8/30
Abstract – 6 April 2010BackgroundSeveral unicellular organisms (prokaryotes and protozoa) can live under permanently anoxic conditions. Although a few metazoans can survive temporarily in the absence of oxygen, it is believed that multi-cellular organisms cannot spend their entire life cycle without free oxygen. Deep seas include some of the most extreme ecosystems on Earth, such as the deep hypersaline anoxic basins of the Mediterranean Sea. These are permanently anoxic systems inhabited by a huge and partly unexplored microbial biodiversity.ResultsDuring the last ten years three oceanographic expeditions were conducted to search for the presence of living fauna in the sediments of the deep anoxic hypersaline L'Atalante basin (Mediterranean Sea). We report here that the sediments of the L'Atalante basin are inhabited by three species of the animal phylum Loricifera (Spinoloricus nov. sp., Rugiloricus nov. sp. and Pliciloricus nov. sp.) new to science. Using radioactive tracers, biochemical analyses, quantitative X-ray microanalysis and infrared spectroscopy, scanning and transmission electron microscopy observations on ultra-sections, we provide evidence that these organisms are metabolically active and show specific adaptations to the extreme conditions of the deep basin, such as the lack of mitochondria, and a large number of hydrogenosome-like organelles, associated with endosymbiotic prokaryotes.ConclusionsThis is the first evidence of a metazoan life cycle that is spent entirely in permanently anoxic sediments. Our findings allow us also to conclude that these metazoans live under anoxic conditions through an obligate anaerobic metabolism that is similar to that demonstrated so far only for unicellular eukaryotes. The discovery of these life forms opens new perspectives for the study of metazoan life in habitats lacking molecular oxygen.
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Animals use O2 and produce CO2
• Circulation systems move gasses (and other essential resources such as nutrients, hormones, etc) throughout the animal’s body
• Respiratory systems exchange gasses with the environment
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Circulation systems have evolved over time
• The most primitive animals exchange gasses and circulate resources entirely by diffusionProcess is slow and cannot support 3-D large
bodies• Sponges, jellies and flatworms use diffusion
alone
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Critical Thinking
• Why isn’t diffusion adequate for exchange in a 3D large animal???
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Critical Thinking
• Why isn’t diffusion adequate for exchange in a 3D large animal???
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Critical Thinking
• But…..plants rely on diffusion for gas exchange…..how do they get so big???
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Critical Thinking
• But…..plants rely on diffusion for gas exchange…..how do they get so big???
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Circulation systems have evolved over time
• The most primitive animals exchange gasses and circulate resources entirely by diffusionProcess is slow and cannot support 3-D large
bodiesSurface area / volume ratio becomes too small
• Sponges, jellies and flatworms use diffusion alone
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Diagram of sponge structure
Virtually every cell in a sponge is in direct contact with the water – little circulation is
required
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Diagram of jellyfish structure, and photos
• Jellies and flatworms have thin bodies and elaborately branched gastrovascular cavitiesAgain, all cells are very close to the external
environmentThis facilitates diffusionSome contractions help circulate (contractile
fibers in jellies, muscles in flatworms)
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Diagram of open circulatory system in a grasshopper
Circulation systems have evolved over time
Metabolic energy is used to pump hemolymph through blood vessels into the body cavity
Hemolymph is returned to vessels via ostia – pores that draw in the fluid as the heart relaxes
• Most invertebrates (esp. insects) have an open circulatory system
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Diagram of a closed circulatory system, plus a diagram showing an earthworm circulatory system
Circulation systems have evolved over time
Metabolic energy is used to pump blood through blood vessels
Blood is contained within the vessels
Exchange occurs by diffusion in capillary beds
• Closed circulatory systems separate blood from interstitial fluid
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Open vs. Closed…both systems are common
Open systems…. • Use less metabolic
energy to run• Use less metabolic
energy to build• Can function as a
hydrostatic skeleton
• Most invertebrates (except earthworms and larger mollusks) have open systems
Closed systems….• Maintain higher
pressure • Are more effective
at transport• Supply more
oxygen to support larger and more active animals
• All vertebrates have closed systems
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All vertebrates have a closed circulatory system
• Chambered heart pumps bloodAtria receive bloodVentricles pump blood
• Vessels contain the bloodVeins carry blood to atriaArteries carry blood from ventricles
• Capillary beds facilitate exchangeCapillary beds separate arteries from veinsHighly branched and very tinyInfiltrate all tissues in the body We’ll go over these
step by step
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Diagram of a chambered heart
Chambered heart pumps blood• Atria receive blood
• Ventricles pump blood
• One-way valves direct blood flow
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Critical Thinking
• Atria receive blood; ventricles pump• Given that function, what structure would
you predict???
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Critical Thinking
• Atria receive blood; ventricles pump• Given that function, what structure would
you predict???
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Diagram of a chambered heart
Chambered heart pumps blood• Atria receive blood
Soft walled, flexible• Ventricles pump
bloodThick, muscular
walls• One-way valves
direct blood flow
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Diagram showing artery, vein and capillary bed
Vessels contain the blood• Arteries carry blood
from ventriclesAlways under pressure
• Veins carry blood to atriaOne-way valves
prevent back flowBody movements
increase circulationPressure is always low
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Diagram of blood circulation pattern in humans
Note that blood vessel names reflect the direction of flow, NOT the amount of
oxygen in the blood
• Arteries carry blood AWAY from the heartArterial blood is always
under pressureIt is NOT always
oxygenated• Veins carry blood TO
the heart
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Diagram showing artery, vein and capillary bed
Capillary beds facilitate exchange
• Capillary beds separate arteries from veins• Highly branched and very tiny• Infiltrate all tissues in the body• More later
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All vertebrates have a closed circulatory system – REVIEW
• Chambered heart pumps bloodAtria receive bloodVentricles pump blood
• Vessels contain the bloodVeins carry blood to atriaArteries carry blood from ventricles
• Capillary beds facilitate exchangeCapillary beds separate arteries from veinsHighly branched and very tinyInfiltrate all tissues in the body
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Diagram showing progression from a 1-chambered heart to a 4-chambered heart. This diagram is used in the next 12 slides.
Evolution of double circulation – not all animals have a 4-chambered heart
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Fishes have a 2-chambered heart
• One atrium, one ventricle• A single pump of the heart
circulates blood through 2 capillary beds in a single circuitBlood pressure drops as blood
enters the capillaries (increase in cross-sectional area of vessels)
Blood flow to systemic capillaries and back to the heart is very slow
Flow is increased by swimming movements
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Two circuits increases the efficiency of gas exchange = double circulation
• One circuit goes to exchange surface• One circuit goes to body systems• Both under high pressure – increases flow rate
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Amphibians have a 3-chambered heart• Two atria, one ventricle• Ventricle pumps to 2 circuits
One circuit goes to lungs and skin to release CO2 and acquire O2
The other circulates through body tissues
• Oxygen rich and oxygen poor blood mix in the ventricleA ridge helps to direct flow
• Second pump increases the speed of O2 delivery to the body
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Most reptiles also have a 3-chambered heart
• A partial septum further separates the blood flow and decreases mixingCrocodilians have a complete
septum• Point of interest: reptiles have
two arteries that lead to the systemic circuitsArterial valves help direct blood
flow away from pulmonary circuit when animal is submerged
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Critical Thinking
• What is a disadvantage of a 3 chambered heart???
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Critical Thinking
• What is a disadvantage of a 3 chambered heart???
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Mammals and birds have 4-chambered hearts
• Two atria and two ventricles• Oxygen rich blood is completely
separated from oxygen poor bloodNo mixing much more efficient gas
transportEfficient gas transport is essential
for both movement and support of endothermy
Endotherms use 10-30x more energy to maintain body temperatures
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Mammals and birds have 4-chambered hearts
• Mammals and birds are NOT monophyletic
• What does this mean???
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Phylogenetic tree showing the diversification of vertebrates
Mammals and birds have 4-chambered hearts
• Mammals and birds are NOT monophyletic
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Mammals and birds have 4-chambered hearts
• Mammals and birds are NOT monophyletic
• Four-chambered hearts evolved independently
• What’s this called???
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Mammals and birds have 4-chambered hearts
• Mammals and birds are NOT monophyletic
• Four-chambered hearts evolved independently
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Review: evolution of double circulation
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Blood Circulation
• Blood vessels are organsOuter layer is elastic connective tissueMiddle layer is smooth muscle and elastic
fibersInner layer is endothelial tissue
• Arteries have thicker walls• Capillaries have only an endothelium and
basement membrane
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Critical Thinking
• Arteries have thicker walls than veins• Capillaries have only an endothelium and
basement membrane• What is the functional significance of this
structural difference???
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Critical Thinking
• Arteries have thicker walls than veins• Capillaries have only an endothelium and
basement membrane• What is the functional significance of this
structural difference???
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Diagram showing artery, vein and capillary bed
Form reflects function…
• Arteries are under more pressure than veins
• Capillaries are the exchange surface
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Graph showing relationships between blood pressure, blood velocity, and the cross-sectional area of different kinds of blood vessels – arteries to capillaries to veins. This same graph is on the next 3 slides.
Blood pressure
and velocity drop as
blood moves through
capillaries
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Total cross-sectional area
in capillary beds is much higher than in
arteries or veins; slows
flow
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Velocity increases as blood passes
into veins (smaller cross-
sectional area);
pressure remains
dissipated
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One-way valves and
body movements force blood back to right heart atrium
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Critical Thinking
• What makes rivers curl on the Coastal Plain???
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Critical Thinking
• What makes rivers curl on the Coastal Plain???
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Emphasize the difference
between velocity and pressure!!!
Velocity increases in the venous system; pressure does
NOT
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Capillary Exchange
• Gas exchange and other transfers occur in the capillary beds
• Muscle contractions determine which beds are “open”Brain, heart, kidneys and liver are generally
always fully openDigestive system capillaries open after a mealSkeletal muscle capillaries open during
exerciseetc…
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Diagram showing sphincter muscle control over capillary flow. Micrograph of a capillary bed.
Bed fully open
Bed closed, through-flow only
Note scale – capillaries are very tiny!!
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Capillary Transport Processes:
• Endocytosis exocytosis across membrane• Diffusion based on electrochemical gradients• Bulk flow between endothelial cells
Water potential gradient forces solution out at arterial end
Reduction in pressure draws most (85%) fluid back in at venous end
Remaining fluid is absorbed into lymph, returned at shoulder ducts
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Capillary Transport Processes:
• Endocytosis exocytosis across membrane• Diffusion based on concentration gradients• Bulk flow between endothelial cells
Water potential gradient forces solution out at arterial end
Reduction in pressure draws most (85%) fluid back in at venous end
Remaining fluid is absorbed into lymph, returned at shoulder ducts
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Bulk Flow in Capillary Beds
• Remember water potential: Ψ = P – s• Remember that in bulk flow P is dominant
No membranePlus, in the capillaries, s is ~stable (blood
proteins too big to pass)• P changes due to the interaction between
arterial pressure and the increase in cross-sectional area
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Diagram showing osmotic changes across a capillary bed
Bulk Flow in Capillary BedsRemember: Ψ = P – s
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Capillary Transport Processes:
• Endocytosis exocytosis across membrane• Diffusion based on concentration gradients• Bulk flow between endothelial cells
Water potential gradient forces solution out at arterial end
Reduction in pressure draws most (85%) fluid back in at venous end
Remaining fluid is absorbed into lymph, returned at shoulder ducts
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Blood structure and function• Blood is ~55% plasma and ~45% cellular
elementsPlasma is ~90% waterCellular elements include red blood cells, white
blood cells and platelets
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Chart listing all blood components – both liquid and cellular
Blood Components
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Plasma Solutes – 10% of plasma volume• Solutes
Inorganic salts that maintain osmotic balance, buffer pH to 7.4, contribute to nerve and muscle function
Concentration is maintained by kidneys• Proteins
Also help maintain osmotic balance and pHEscort lipids (remember, lipids are insoluble in water)Defend against pathogens (antibodies)Assist with blood clotting
• Materials being transportedNutrientsHormonesRespiratory gassesWaste products from metabolism
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Cellular Elements • Red blood cells, white blood cells and
plateletsRed blood cells carry O2 and some CO2
White blood cells defend against pathogensPlatelets promote clotting
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Red Blood Cells
• Most numerous of all blood cells• 5-6 million per mm3 of blood!• 25 trillion in the human body• Biconcave shape• No nucleus, no mitochondria
They don’t use up any of the oxygen they carry!• 250 million molecules of hemoglobin per cell
Each hemoglobin can carry 4 oxygen moleculesMore on hemoglobin later…
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Critical Thinking
• Tiny size and biconcave shape do what???
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Critical Thinking
• Tiny size and biconcave shape do what???
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White Blood Cells• All function in defense against pathogens• We will cover extensively in the chapter on
immune systems
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Platelets
• Small fragments of cells• Formed in bone marrow• Function in blood clotting at wound sites
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Diagram showing the clotting process
The Clotting Process
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Diagram showing blood cell production from stem cells in bone marrow
Blood Cell Production
• Blood cells are constantly digested by the liver and spleenComponents are re-
used
• Pluripotent stem cells produce all blood cells
• Feedback loops that sense tissue oxygen levels control red blood cell production
Fig 42.16, 7th ed
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Key Concepts:
• Circulation and gas exchange – why?• Circulation – spanning diversity• Hearts – the evolution of double circulation• Blood circulation and capillary exchange• Blood structure and function• Gas exchange – spanning diversity• Breathing – spanning diversity• Respiratory pigments
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Hands On
• Dissect out the circulatory system of your rat
• Start by clearing the tissues around the heart
• Be especially careful at the anterior end of the heart – this is where the major blood vessels emerge
• Trace the aorta, the vena cava, and as many additional vessels as possible – use your manual and lab handout for direction!
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Hands On
• Feel and describe the texture of the atria vs. the ventricles
• Take cross sections of the heart through both the atria and the ventricles
• Examine under the dissecting microscope• Do the same with aorta and vena cava• Try for a thin enough section to look at
under the compound microscope too
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Gas Exchange
• Gas Exchange ≠ Respiration ≠ BreathingGas exchange = delivery of O2; removal of
CO2
Respiration = the metabolic process that occurs in mitochondria and produces ATP
Breathing = ventilation to supply the exchange surface with O2 and allow exhalation of CO2
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Diagram showing indirect links between external environment, respiratory system, circulatory system and tissues.
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Gas Exchange Occurs at the Respiratory Surface
• Respiratory medium = the source of the O2
Air for terrestrial animals – air is 21% O2 by volume
Water for aquatic animals – dissolved O2 varies base on environmental conditions, especially salinity and temperature; always lower than in air
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Gas Exchange Occurs at the Respiratory Surface
• Respiratory surface = the site of gas exchangeGasses move by diffusion across membranesGasses are always dissolved in the interstitial
fluid• Surface area is important!
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Evolution of Gas Exchange Surfaces
• SkinMust remain moist – limits environmentsMust maintain functional SA / V ratio – limits
3D size• Gills
Large SA suspended in water• Tracheal systems
Large SA spread diffusely throughout body• Lungs
Large SA contained within small space
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Skin Limits
• Sponges, jellies and flatworms rely on the skin as their only respiratory surface
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Evolution of Gas Exchange Surfaces
• SkinMust remain moist – limits environmentsMust maintain functional SA / V ratio – limits
3D size• Gills
Large SA suspended in water• Tracheal systems
Large SA spread diffusely throughout body• Lungs
Large SA contained within small space
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Diagrams and photos of gills in different animals.
Invertebrate Gills
• Dissolved oxygen is limited
• Behaviors and structures increase water flow past gills to maximize gas exchange
Fig 42.20, 7th ed
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Diagram of countercurrent exchange in fish gills
Countercurrent Exchange in Fish Gills• Direction of blood flow allows for maximum
gas exchange – maintains high gradient
Fig 42.21, 7th ed
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Figure showing countercurrent vs co-current flow effects on diffusion
How countercurrent flow maximizes diffusion
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Evolution of Gas Exchange Surfaces
• SkinMust remain moist – limits environmentsMust maintain functional SA / V ratio – limits
3D size• Gills
Large SA suspended in water• Tracheal systems
Large SA spread diffusely throughout body• Lungs
Large SA contained within small space
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Diagram and micrograph of insect tracheal system.
Tracheal Systems in Insects
• Air tubes diffusely penetrate entire body• Small openings to the outside limit
evaporation• Open circulatory system does not transport
gasses from the exchange surface• Body movements ventilate
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Tracheal Systems in InsectsRings of chitin
Look familiar???
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Critical Thinking
• Name 2 other structures that are held open by rings
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• Name 2 other structures that are held open by rings
Critical Thinking
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Evolution of Gas Exchange Surfaces
• SkinMust remain moist – limits environmentsMust maintain functional SA / V ratio – limits
3D size• Gills
Large SA suspended in water• Tracheal systems
Large SA spread diffusely throughout body• Lungs
Large SA contained within small space
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Lungs in Spiders, Terrestrial Snails and Vertebrates
• Large surface area restricted to small part of the body
• Single, small opening limits evaporation• Connected to all cells and tissues via a
circulatory systemDense capillary beds lie directly adjacent to
respiratory epithelium• In some animals, the skin supplements
gas exchange (amphibians)
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Mammalian Lungs• Highly branched system of tubes – trachea,
bronchi, and bronchioles• Each ends in a cluster of “bubbles” – the
alveoliAlveoli are surrounded by capillariesThis is the actual site of gas exchangeHuge surface area (100m2 in humans)
• Rings of cartilage keep the trachea open• Epiglottis directs food to esophagus
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Figure and micrograph of lung and alveolus structure.
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Mammalian Lungs• Highly branched system of tubes – trachea,
bronchi, and bronchioles• Each ends in a cluster of “bubbles” – the
alveoliAlveoli are surrounded by capillariesThis is the actual site of gas exchangeHuge surface area (100m2 in humans)
• Rings of cartilage keep the trachea open• Epiglottis directs food to esophagus
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Figure of vascularized alveolus
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Mammalian Lungs• Highly branched system of tubes – trachea,
bronchi, and bronchioles• Each ends in a cluster of “bubbles” – the
alveoliAlveoli are surrounded by capillariesThis is the actual site of gas exchangeHuge surface area (100m2 in humans)
• Rings of cartilage keep the trachea open• Epiglottis directs food to esophagus
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Breathing Ventilates Lungs
• Positive pressure breathing – amphibiansAir is forced into trachea under pressureMouth and nose close, muscle contractions
force air into lungsRelaxation of muscles and elastic recoil of lungs
force exhalation
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Breathing Ventilates Lungs
• Positive pressure breathing – amphibiansAir is forced into trachea under pressureMouth and nose close, muscle contractions
force air into lungsRelaxation of muscles and elastic recoil of lungs
force exhalation• Negative pressure breathing – mammals
Air is sucked into trachea under suction• Circuit flow breathing – birds
Air flows through entire circuit with every breath
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Diagram of negative pressure breathing
Negative Pressure Breathing
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Breathing Ventilates Lungs
• Positive pressure breathing – amphibiansAir is forced into trachea under pressureMouth and nose close, muscle contractions
force air into lungsRelaxation of muscles and elastic recoil of lungs
forces exhalation• Negative pressure breathing – mammals
Air is sucked into trachea under suction• Circuit flow breathing – birds
Air flows through entire circuit with every breath
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Diagram of circuit flow breathing in birds
Flow Through Breathing• No residual air left in lungs• Every breath brings fresh O2 past the exchange
surface• Higher lung O2 concentration than in mammals
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Critical Thinking
• What is the functional advantage of flow-through breathing for birds???
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Critical Thinking
• What is the functional advantage of flow-through breathing for birds???
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Respiratory pigments – tying the two systems together
• Respiratory pigments are proteins that reversibly bind O2 and CO2
• Circulatory systems transport the pigments to sites of gas exchange
• O2 and CO2 molecules bind or are released depending on gradients of partial pressure
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Partial Pressure Gradients Drive Gas Transport
• Atmospheric pressure at sea level is equivalent to the pressure exerted by a column of mercury 760 mm high = 760 mm HgThis represents the total pressure that the
atmosphere exerts on the surface of the earth• Partial pressure is the percentage of total
atmospheric pressure that can be assigned to each component of the atmosphere
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Atmospheric pressure at sea level is equivalent to the pressure exerted by
a column of mercury 760 mm high = 760 mm Hg (29.92” of mercury)
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Partial Pressure Gradients Drive Gas Transport
• Atmospheric pressure at sea level is equivalent to the pressure exerted by a column of mercury 760 mm high = 760 mm HgThis represents the total pressure that the
atmosphere exerts on the surface of the earth• Partial pressure is the percentage of total
atmospheric pressure that can be assigned to each component of the atmosphere
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Partial Pressure Gradients Drive Gas Transport
• Each gas contributes to total atmospheric pressure in proportion to its volume % in the atmosphereEach gas contributes a part of total pressureThat part = the partial pressure for that gas
• The atmosphere is 21% O2 and 0.03% CO2
Partial pressure of O2 is 0.21x760 = 160 mm Hg
Partial pressure of CO2 is 0.0003x760 = 0.23 mm Hg
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Partial Pressure Gradients Drive Gas Transport
• Each gas contributes to total atmospheric pressure in proportion to its volume % in the atmosphereEach gas contributes a part of total pressureThat part = the partial pressure for that gas
• The atmosphere is 21% O2 and 0.03% CO2
Partial pressure of O2 is 0.21x760 = 160 mm Hg
Partial pressure of CO2 is 0.0003x760 = 0.23 mm Hg
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Partial Pressure Gradients Drive Gas Transport
• Atmospheric gasses dissolve into water in proportion to their partial pressure and solubility in waterDynamic equilibriums can eventually develop
such that the PP in solution is the same as the PP in the atmosphere
This occurs in the fluid lining the alveoli
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Critical Thinking
• If a dynamic equilibrium exists in the alveoli, will the partial pressures be the same as in the outside atmosphere???
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Critical Thinking
• If a dynamic equilibrium exists in the alveoli, will the partial pressures be the same as in the outside atmosphere???
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Diagram showing partial pressures of gasses in various parts of the body. This diagram is used in the next 3 slides.
• Inhaled air PP’s = atmospheric PP’s
• Alveolar PP’s reflect mixing of inhaled and exhaled airLower PP of O2 and
higher PP of CO2 than in atmosphere
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• O2 and CO2 diffuse based on gradients of partial pressureBlood PP’s reflect supply
and usageBlood leaves the lungs
with high PP of O2
Body tissues have lower PP of O2 because of mitochondrial usage
O2 moves from blood to tissues
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• Same principles with CO2 Blood leaves the lungs
with low PP of CO2
Body tissues have higher PP of CO2 because of mitochondrial production
CO2 moves from tissues to blood
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• When blood reaches the lungs the gradients favor diffusion of O2 into the blood and CO2 into the alveoli
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Diagram of hemoglobin structure and how it changes with oxygen loading. This diagram is used in the next 3 slides.
Oxygen Transport
• Oxygen is not very soluble in water (blood)• Oxygen transport and delivery are
enhanced by binding of O2 to respiratory pigments
Fig 42.28, 7th ed
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Oxygen Transport• Increase is 2 orders of magnitude!• Almost 50 times more O2 can be carried this
way, as opposed to simply dissolved in the blood
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Oxygen Transport
• Most vertebrates and some inverts use hemoglobin for O2 transport
• Iron (in heme group) is the binding element
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Oxygen Transport
• Four heme groups per hemoglobin, each with one iron atom
• Binding is reversible and cooperative
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Critical Thinking
• Binding is reversible and cooperative• What does that mean???
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Critical Thinking
• Binding is reversible and cooperative• What does that mean???
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Oxygen Transport
• Reverse occurs during unloading• Release of one O2 induces shape change
that speeds up the release of the next 3
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Graph showing how hemoglobin oxygen saturation changes with activity.
Oxygen Transport
• More active metabolism (ie: during muscle use) increases unloading
• Note steepness of curveO2 is unloaded
quickly when metabolic use increases
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Graph showing the Bohr Shift
Oxygen Transport – the Bohr Shift
• More active metabolism also increases the release of CO2
Converts to carbonic acid, acidifying blood
pH change stimulates release of additional O2
Fig 42.29, 7th ed
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Figure showing how carbon dioxide is transported from tissues to lungs. This figure is used in the next 3 slides.
Carbon Dioxide Transport
• Red blood cells also assist in CO2 transport7% of CO2 is transported
dissolved in plasma23% is bound to amino groups of
hemoglobin in the RBC’s70% is converted to bicarbonate
ions inside the RBC’s
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Carbon Dioxide Transport
• CO2 in RBC’s reacts with water to form carbonic acid (H2CO3)
• H2CO3 dissociates to bicarbonate (HCO3
-) and H+
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Carbon Dioxide Transport
• Most H+ binds to hemoglobinThis limits blood
acidification
• HCO3- diffuses
back into plasma for transport
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Carbon Dioxide Transport
• Reverse occurs when blood reaches the lungsConversion back to
CO2 is driven by diffusion gradients as CO2 moves into the lungs
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REVIEW – Key Concepts:
• Circulation and gas exchange – why?• Circulation – spanning diversity• Hearts – the evolution of double circulation• Blood circulation and capillary exchange• Blood structure and function• Gas exchange – spanning diversity• Breathing – spanning diversity• Respiratory pigments
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Hands On
• Dissect out the respiratory system of your rat
• Trace the trachea into the lungs• Examine trachea and lungs under the
dissecting microscope• Try for thin enough sections to also
examine with the compound microscope