Lecture #10 – Animal Circulation and Gas Exchange Systems 1

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 2

Animals use O 2 and produce CO 2 • All animals are aerobic 

Lots

of oxygen is required to support active mobility  Some animals use lots of oxygen to maintain body temperature • All animals produce CO 2 aerobic respiration as a byproduct of • Gasses must be exchanged  Oxygen must be acquired from the environment  Carbon dioxide must be released to the environment 3

Except……breaking news!

http://www.biomedcentral.com/1741-7007/8/30

Abstract – 6 April 2010 Background

Several 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.

Results

During 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.

Conclusions

This 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 4 lacking molecular oxygen.

Animals use O 2 and produce CO 2 • 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 5

Circulation systems have evolved over time • The most primitive animals exchange gasses and circulate resources entirely by diffusion  Process is slow and cannot support 3-D large bodies • Sponges, jellies and flatworms use diffusion alone 6

Critical Thinking

• Why isn’t diffusion adequate for exchange in a 3D large animal???

7

Critical Thinking

• Why isn’t diffusion adequate for exchange in a 3D large animal???

• Surface area / volume ratio becomes too small • Remember, area is a square function; volume is a cubic function 8

Critical Thinking

• But…..plants rely on diffusion for gas exchange…..how do they get so big???

9

Critical Thinking

• But…..plants rely on diffusion for gas exchange…..how do they get so big???

• Their living tissue is close to the surface and exposed to air – either in the open atmosphere or in the soil atmosphere 10

Circulation systems have evolved over time • The most primitive animals exchange gasses and circulate resources entirely by diffusion  Process is slow and cannot support 3-D large bodies  Surface area / volume ratio becomes too small • Sponges, jellies and flatworms use diffusion alone 11

Virtually every cell in a sponge is in direct contact with the water – little circulation is required Diagram of sponge structure 12

• Jellies and flatworms have thin bodies and elaborately branched gastrovascular cavities  Again, all cells are very close to the external environment  This facilitates diffusion  Some contractions help circulate (contractile fibers in jellies, muscles in flatworms) Diagram of jellyfish structure, and photos 13

Circulation systems have evolved over time • Most invertebrates (esp. insects) have an open circulatory system  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 Diagram of open circulatory system in a grasshopper 14

Circulation systems have evolved over time • Closed circulatory systems separate blood from interstitial fluid  Metabolic energy is used to pump blood through blood vessels  Blood is contained within the vessels  Exchange occurs by diffusion in capillary beds Diagram of a closed circulatory system, plus a diagram showing an earthworm circulatory system 15

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 16

All vertebrates have a closed circulatory system • Chambered heart pumps blood  Atria receive blood  Ventricles pump blood • Vessels contain the blood  Veins carry blood to atria  Arteries carry blood from ventricles • Capillary beds facilitate exchange  Capillary beds separate arteries from veins  Highly branched and very tiny  Infiltrate all tissues in the body We’ll go over these 17 step by step

Chambered heart pumps blood

• Atria receive blood • Ventricles pump blood Diagram of a chambered heart • One-way valves direct blood flow 18

Critical Thinking

• Atria receive blood; ventricles pump • Given that function, what structure would you predict???

19

Critical Thinking

• Atria receive blood; ventricles pump • Given that function, what structure would you predict???

• Atria are soft, flexible chambers • Ventricles have much more muscular walls 20

Chambered heart pumps blood

• Atria receive blood  Soft walled, flexible • Ventricles pump blood  Thick, muscular walls • One-way valves direct blood flow Diagram of a chambered heart 21

Vessels contain the blood

• Arteries carry blood from ventricles  Always under pressure • Veins carry blood to atria  One-way valves prevent back flow  Body movements increase circulation  Pressure is always low Diagram showing artery, vein and capillary bed 22

Note that blood vessel names reflect the direction of flow, NOT the amount of oxygen in the blood • Arteries carry blood

AWAY

from the heart  Arterial blood is always under pressure  It is NOT always oxygenated • Veins carry blood

TO

the heart Diagram of blood circulation pattern in humans 23

Capillary beds facilitate exchange • Capillary beds separate arteries from veins • Highly branched and very tiny • Infiltrate all tissues in the body • More later Diagram showing artery, vein and capillary bed 24

All vertebrates have a closed circulatory system – REVIEW • Chambered heart pumps blood  Atria receive blood  Ventricles pump blood • Vessels contain the blood  Veins carry blood to atria  Arteries carry blood from ventricles • Capillary beds facilitate exchange  Capillary beds separate arteries from veins  Highly branched and very tiny  Infiltrate all tissues in the body 25

Evolution of double circulation – not all animals have a 4-chambered heart Diagram showing progression from a 1 chambered heart to a 4-chambered heart. This diagram is used in the next 12 slides.

26

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 circuit  Blood 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 27

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 28

Amphibians have a 3-chambered heart • Two atria, one ventricle • Ventricle pumps to 2 circuits  One circuit goes to lungs and skin to release CO 2 and acquire O 2  The other circulates through body tissues • Oxygen rich and oxygen poor blood mix in the ventricle  A ridge helps to direct flow • Second pump increases the speed of O 2 delivery to the body 29

Most reptiles also have a 3-chambered heart • • A partial septum further separates the blood flow and decreases mixing  Crocodilians have a complete septum

Point of interest: reptiles have two arteries that lead to the systemic circuits



Arterial valves help direct blood flow away from pulmonary circuit when animal is submerged

30

Critical Thinking

• What is a disadvantage of a 3 chambered heart???

31

Critical Thinking

• What is a disadvantage of a 3 chambered heart???

• Oxygen rich and oxygen poor blood mix in the ventricle • Less than maximum efficiency 32

Mammals and birds have 4-chambered hearts • Two atria and two ventricles • Oxygen rich blood is completely separated from oxygen poor blood  No mixing  gas transport much more efficient  Efficient gas transport is essential for both movement and support of endothermy  Endotherms use 10-30x more energy to maintain body temperatures 33

Mammals and birds have 4-chambered hearts • Mammals and birds are NOT monophyletic • What does this mean???

34

Mammals and birds have 4-chambered hearts • Mammals and birds are NOT monophyletic • Mammals and birds evolved from separate reptilian ancestors Phylogenetic tree showing the diversification of vertebrates 35

Mammals and birds have 4-chambered hearts • Mammals and birds are NOT monophyletic • Four-chambered hearts evolved independently • What’s this called???

36

Mammals and birds have 4-chambered hearts • Mammals and birds are NOT monophyletic • Four-chambered hearts evolved independently • Convergent evolution 37

Review: evolution of double circulation 38

Blood Circulation

• Blood vessels are organs  Outer layer is elastic connective tissue  Middle layer is smooth muscle and elastic fibers  Inner layer is endothelial tissue • Arteries have thicker walls • Capillaries have only an endothelium and basement membrane 39

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???

40

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???

• Arteries are under more pressure than veins • Capillaries are the exchange surface 41

Form reflects function…

• Arteries are under more pressure than veins • Capillaries are the exchange surface Diagram showing artery, vein and capillary bed 42

Blood pressure and velocity drop as blood moves through capillaries

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.

43

Total cross sectional area in capillary beds is much higher than in arteries or veins; slows flow 44

Velocity increases as blood passes into veins (smaller cross sectional area); pressure remains dissipated 45

One-way valves and body movements force blood back to right heart atrium 46

Critical Thinking

• What makes rivers curl on the Coastal Plain???

47

Critical Thinking

• What makes rivers curl on the Coastal Plain???

• Velocity is controlled by gravity in rivers • The Coastal Plain is just a few meters above sea level – little gravity to force forward momentum • The water slows; the rivers meander • The functional equivalent to blood meandering through a capillary bed 48

Emphasize the difference between velocity and pressure!!!

Velocity increases in the venous system; pressure does NOT 49

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 open  Digestive system capillaries open after a meal  Skeletal muscle capillaries open during exercise  etc… 50

Bed fully open Bed closed, through flow only Note scale – capillaries are very tiny!!

Diagram showing sphincter muscle control over capillary flow. Micrograph of a capillary bed.

51

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 52

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 53

Bulk Flow in Capillary Beds

• Remember water potential: Ψ = P – s • Remember that in bulk flow P is dominant  No membrane  Plus, 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 54

Bulk Flow in Capillary Beds

Remember: Ψ = P – s Diagram showing osmotic changes across a capillary bed 55

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 56

Blood structure and function

• Blood is ~55% plasma and ~45% cellular elements  Plasma is ~90% water  Cellular elements include red blood cells, white blood cells and platelets 57

Blood Components

Chart listing all blood components – both liquid and cellular 58

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 pH  Escort lipids (remember, lipids are insoluble in water)  Defend against pathogens (antibodies)  Assist with blood clotting • Materials being transported  Nutrients  Hormones  Respiratory gasses  Waste products from metabolism 59

Cellular Elements

• Red blood cells, white blood cells and platelets  Red blood cells carry O 2 and some CO 2  White blood cells defend against pathogens  Platelets promote clotting 60

Red Blood Cells

• Most numerous of all blood cells • 5-6 million per mm 3 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 molecules  More on hemoglobin later… 61

Critical Thinking

• Tiny size and biconcave shape do what???

62

Critical Thinking

• Tiny size and biconcave shape do what???

• Increase surface area 63

White Blood Cells

• All function in defense against pathogens • We will cover extensively in the chapter on immune systems 64

Platelets

• Small fragments of cells • Formed in bone marrow • Function in blood clotting at wound sites 65

The Clotting Process

Diagram showing the clotting process 66

Blood Cell Production

• Blood cells are constantly digested by the liver and spleen  Components 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, 7 th ed Diagram showing blood cell production from stem cells in bone marrow 67

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 68

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!

69

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 70

Gas Exchange • Gas Exchange ≠ Respiration ≠ Breathing  Gas exchange = delivery of O 2 ; removal of CO 2  Respiration = the metabolic process that occurs in mitochondria and produces ATP  Breathing = ventilation to supply the exchange surface with O 2 and allow exhalation of CO 2 71

Diagram showing indirect links between external environment, respiratory system, circulatory system and tissues.

72

Gas Exchange Occurs at the Respiratory Surface • Respiratory medium = the source of the O 2  Air for terrestrial animals – air is 21% O 2 volume by  Water for aquatic animals – dissolved O 2 varies base on environmental conditions, especially salinity and temperature; always lower than in air 73

Gas Exchange Occurs at the Respiratory Surface • Respiratory surface = the site of gas exchange  Gasses move by diffusion across membranes  Gasses are always dissolved in the interstitial fluid • Surface area is important!

74

Evolution of Gas Exchange Surfaces • Skin  Must remain moist – limits environments  Must 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 75

Skin Limits

• Sponges, jellies and flatworms rely on the skin as their only respiratory surface 76

Evolution of Gas Exchange Surfaces • Skin  Must remain moist – limits environments  Must 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 77

Invertebrate Gills

• Dissolved oxygen is limited • Behaviors and structures increase water flow past gills to maximize gas exchange Diagrams and photos of gills in different animals.

78 Fig 42.20, 7 th ed

Countercurrent Exchange in Fish Gills • Direction of blood flow allows for maximum gas exchange – maintains high gradient Diagram of countercurrent exchange in fish gills 79 Fig 42.21, 7 th ed

How countercurrent flow maximizes diffusion Figure showing countercurrent vs co-current flow effects on diffusion 80

Evolution of Gas Exchange Surfaces • Skin  Must remain moist – limits environments  Must 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 81

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 Diagram and micrograph of insect tracheal system.

82

Tracheal Systems in Insects

Rings of chitin Look familiar???

83

Critical Thinking

• Name 2 other structures that are held open by rings 84

Critical Thinking

• Name 2 other structures that are held open by rings • Xylem cells by rings of lignin • Vertebrate trachea by rings of cartilage Diagrams and micrographs of tracheae, xylem and trachea 85

Evolution of Gas Exchange Surfaces • Skin  Must remain moist – limits environments  Must 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 86

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 system  Dense capillary beds lie directly adjacent to respiratory epithelium • In some animals, the skin supplements gas exchange (amphibians) 87

Mammalian Lungs

• Highly branched system of tubes – trachea, bronchi, and bronchioles • Each ends in a cluster of “bubbles” – the alveoli  Alveoli are surrounded by capillaries  This is the actual site of gas exchange  Huge surface area (100m 2 in humans) • Rings of cartilage keep the trachea open • Epiglottis directs food to esophagus 88

Figure and micrograph of lung and alveolus structure.

89

Mammalian Lungs

• Highly branched system of tubes – trachea, bronchi, and bronchioles • Each ends in a cluster of “bubbles” – the alveoli  Alveoli are surrounded by capillaries  This is the actual site of gas exchange  Huge surface area (100m 2 in humans) • Rings of cartilage keep the trachea open • Epiglottis directs food to esophagus 90

Figure of vascularized alveolus 91

Mammalian Lungs

• Highly branched system of tubes – trachea, bronchi, and bronchioles • Each ends in a cluster of “bubbles” – the alveoli  Alveoli are surrounded by capillaries  This is the actual site of gas exchange  Huge surface area (100m 2 in humans) • Rings of cartilage keep the trachea open • Epiglottis directs food to esophagus 92

Breathing Ventilates Lungs

• Positive pressure breathing – amphibians  Air is forced into trachea under pressure  Mouth and nose close, muscle contractions force air into lungs  Relaxation of muscles and elastic recoil of lungs force exhalation 93

Breathing Ventilates Lungs

• Positive pressure breathing – amphibians  Air is forced into trachea under pressure  Mouth and nose close, muscle contractions force air into lungs  Relaxation 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 94

Negative Pressure Breathing

Diagram of negative pressure breathing 95

Breathing Ventilates Lungs

• Positive pressure breathing – amphibians  Air is forced into trachea under pressure  Mouth and nose close, muscle contractions force air into lungs  Relaxation 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 96

Flow Through Breathing • No residual air left in lungs • Every breath brings fresh O 2 surface • Higher lung O 2 past the exchange concentration than in mammals Diagram of circuit flow breathing in birds 97

Critical Thinking

• What is the functional advantage of flow through breathing for birds???

98

Critical Thinking

• What is the functional advantage of flow through breathing for birds???

• More oxygen = more ATP = more energy • Flight requires a LOT of energy 99

Respiratory pigments – tying the two systems together • Respiratory pigments are proteins that reversibly bind O 2 and CO 2 • Circulatory systems transport the pigments to sites of gas exchange • O 2 and CO 2 molecules bind or are released depending on gradients of partial pressure 100

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 Hg  This 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 101

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) 102

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 Hg  This 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 103

Partial Pressure Gradients Drive Gas Transport • Each gas contributes to total atmospheric pressure in proportion to its volume % in the atmosphere  Each gas contributes a part of total pressure  That part = the partial pressure for that gas • The atmosphere is 21% O 2 CO 2  Partial pressure of O 2 Hg and 0.03% is 0.21x760 = 160 mm  Partial pressure of CO 2 mm Hg is 0.0003x760 = 0.23 104

Partial Pressure Gradients Drive Gas Transport • Each gas contributes to total atmospheric pressure in proportion to its volume % in the atmosphere  Each gas contributes a part of total pressure  That part = the partial pressure for that gas • The atmosphere is 21% O 2 CO 2  Partial pressure of O 2 Hg and 0.03% is 0.21x760 = 160 mm  Partial pressure of CO 2 mm Hg is 0.0003x760 = 0.23 105

Partial Pressure Gradients Drive Gas Transport • Atmospheric gasses dissolve into water in proportion to their partial pressure and solubility in water  Dynamic 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 106

Critical Thinking

• If a dynamic equilibrium exists in the alveoli, will the partial pressures be the same as in the outside atmosphere???

107

Critical Thinking

• If a dynamic equilibrium exists in the alveoli, will the partial pressures be the same as in the outside atmosphere???

• NO!!!

 Breathing does not completely replace alveolar air with fresh air  The PP of O 2 is lower and the PP of CO 2 is higher in the alveoli than in the atmosphere 108

• Inhaled air PP’s = atmospheric PP’s • Alveolar PP’s reflect mixing of inhaled and exhaled air  Lower PP of O 2 and higher PP of CO 2 than in atmosphere Diagram showing partial pressures of gasses in various parts of the body. This diagram is used in the next 3 slides.

109

• O 2 and CO 2 diffuse based on gradients of partial pressure  Blood PP’s reflect supply and usage  Blood leaves the lungs with high PP of O 2  Body tissues have lower PP of O 2 because of mitochondrial usage  O 2 moves from blood to tissues 110

• Same principles with CO 2  Blood leaves the lungs with low PP of CO 2  Body tissues have higher PP of CO 2 because of mitochondrial production  CO 2 moves from tissues to blood 111

• When blood reaches the lungs the gradients favor diffusion of O 2 into the blood and CO 2 into the alveoli 112

Oxygen Transport

• Oxygen is not very soluble in water (blood) • Oxygen transport and delivery are enhanced by binding of O 2 to respiratory pigments Diagram of hemoglobin structure and how it changes with oxygen loading. This diagram is used in the next 3 slides.

113 Fig 42.28, 7 th ed

Oxygen Transport

• Increase is 2 orders of magnitude!

• Almost 50 times more O 2 can be carried this way, as opposed to simply dissolved in the blood 114

Oxygen Transport

• Most vertebrates and some inverts use hemoglobin for O 2 transport • Iron (in heme group) is the binding element 115

Oxygen Transport

• Four heme groups per hemoglobin, each with one iron atom • Binding is reversible and cooperative 116

Critical Thinking

• Binding is reversible and cooperative • What does that mean???

117

Critical Thinking

• Binding is reversible and cooperative • What does that mean???

• Binding one O 2 induces shape change that speeds up the binding of the next 3 • Remember, hemoglobin is a protein!

 Binding events are both chemical and physical 118

Oxygen Transport

• Reverse occurs during unloading • Release of one O 2 induces shape change that speeds up the release of the next 3 119

Oxygen Transport

• More active metabolism (ie: during muscle use) increases unloading • Note steepness of curve  O 2 is unloaded quickly when metabolic use increases Graph showing how hemoglobin oxygen saturation changes with activity.

120

Oxygen Transport – the Bohr Shift

• More active metabolism also increases the release of CO 2  Converts to carbonic acid, acidifying blood  pH change stimulates release of additional O 2 Fig 42.29, 7 th ed Graph showing the Bohr Shift 121

Carbon Dioxide Transport

• Red blood cells also assist in CO 2 transport  7% of CO 2 is transported dissolved in plasma  23% is bound to amino groups of hemoglobin in the RBC’s  70% is converted to bicarbonate ions inside the RBC’s Figure showing how carbon dioxide is transported from tissues to lungs. This figure is used in the next 3 slides.

122

Carbon Dioxide Transport • CO 2 in RBC’s reacts with water to form carbonic acid (H 2 CO 3 ) • H 2 CO 3 dissociates to bicarbonate (HCO 3 ) and H + 123

Carbon Dioxide Transport • Most H + binds to hemoglobin  This limits blood acidification • HCO 3 diffuses back into plasma for transport 124

Carbon Dioxide Transport • Reverse occurs when blood reaches the lungs  Conversion back to CO 2 is driven by diffusion gradients as CO 2 moves into the lungs 125

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 126

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 127