Lecture 10 – Animal Circulation and Gas Exchange Systems

1
Lecture 10 Animal Circulation and Gas Exchange
Systems
2
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

3
Animals use O2 and produce CO2

• 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 CO2 as a byproduct of
  aerobic respiration
• Gasses must be exchanged
• Oxygen must be acquired from the environment
• Carbon dioxide must be released to the environment

4
Animals use O2 and produce CO2

• Circulation systems move gasses (and other
  essential resources such as nutrients, hormones,
  etc) throughout the animals 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 isnt diffusion adequate for exchange in a 3D
  large animal???

7
Critical Thinking

• Why isnt 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. Closedboth 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

Well go over these step by step
17
Chambered heart pumps blood

• Atria receive blood
• Ventricles pump blood
• One-way valves direct blood flow

Diagram of a chambered heart
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
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

26
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.
27
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

28
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

29
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
  ventricle
• A ridge helps to direct flow
• Second pump increases the speed of O2 delivery to
  the body

30
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

31
Critical Thinking

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

32
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

33
Mammals and birds have 4-chambered hearts

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

34
Mammals and birds have 4-chambered hearts

• Mammals and birds are NOT monophyletic
• What does this mean???

35
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
36
Mammals and birds have 4-chambered hearts

• Mammals and birds are NOT monophyletic
• Four-chambered hearts evolved independently
• Whats this called???

37
Mammals and birds have 4-chambered hearts

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

38
Review evolution of double circulation
39
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

40
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

41
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???

42
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

43
Form reflects function

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

Diagram showing artery, vein and capillary bed
44
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.
45
Total cross-sectional area in capillary beds is
much higher than in arteries or veins slows flow
46
Velocity increases as blood passes into veins
(smaller cross-sectional area) pressure remains
dissipated
47
One-way valves and body movements force blood
back to right heart atrium
48
Critical Thinking

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

49
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

50
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

51
Bed fully openBed closed, through-flow
onlyNote scale capillaries are very tiny!!
Diagram showing sphincter muscle control over
capillary flow. Micrograph of a capillary bed.
52
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

53
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

54
Bulk Flow in Capillary Beds

• Remember water potential ? 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

55
Bulk Flow in Capillary BedsRemember ? P s
Diagram showing osmotic changes across a
capillary bed
56
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

57
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

58
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

59
Blood Components
Chart listing all blood components both liquid
and cellular
60
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

61
Cellular Elements

• Red blood cells, white blood cells and platelets
• Red blood cells carry O2 and some CO2
• White blood cells defend against pathogens
• Platelets promote clotting

62
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 dont 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

63
Critical Thinking

• Tiny size and biconcave shape do what???

64
Critical Thinking

• Tiny size and biconcave shape do what???
• Increase surface area

65
White Blood Cells

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

66
Platelets

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

67
The Clotting Process
Diagram showing the clotting process
68
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

Diagram showing blood cell production from stem
cells in bone marrow
Fig 42.16, 7th ed
69
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

70
Gas Exchange

• Gas Exchange ? Respiration ? Breathing
• Gas 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

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 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

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.
Fig 42.20, 7th ed
78
Countercurrent Exchange in Fish Gills

• Direction of blood flow allows for maximum gas
  exchange maintains high gradient

Diagram of countercurrent exchange in fish gills
Fig 42.21, 7th ed
79
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 InsectsRings of chitinLook
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 (100m2 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 (100m2 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 (100m2 in humans)
• Rings of cartilage keep the trachea open
• Epiglottis directs food to esophagus

92
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

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

94
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

95
Negative Pressure Breathing
Diagram of negative pressure breathing
96
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

97
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

Diagram of circuit flow breathing in birds
98
Critical Thinking

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

99
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

100
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

101
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

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
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)
104
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

105
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 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

106
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 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

107
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

108
Critical Thinking

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

109
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 O2 is lower and the PP of CO2 is higher
  in the alveoli than in the atmosphere

110
Diagram showing partial pressures of gasses in
various parts of the body. This diagram is used
in the next 3 slides.

• Inhaled air PPs atmospheric PPs
• Alveolar PPs reflect mixing of inhaled and
  exhaled air
• Lower PP of O2 and higher PP of CO2 than in
  atmosphere

111

• O2 and CO2 diffuse based on gradients of partial
  pressure
• Blood PPs reflect supply and usage
• Blood 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

112

• 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

113

• When blood reaches the lungs the gradients favor
  diffusion of O2 into the blood and CO2 into the
  alveoli

114
Oxygen Transport

• Oxygen is not very soluble in water (blood)
• Oxygen transport and delivery are enhanced by
  binding of O2 to respiratory pigments

Diagram of hemoglobin structure and how it
changes with oxygen loading. This diagram is
used in the next 3 slides.
Fig 42.28, 7th ed
115
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

116
Oxygen Transport

• Most vertebrates and some inverts use hemoglobin
  for O2 transport
• Iron (in heme group) is the binding element

117
Oxygen Transport

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

118
Critical Thinking

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

119
Critical Thinking

• Binding is reversible and cooperative
• What does that mean???
• Binding one O2 induces shape change that speeds
  up the binding of the next 3
• Remember, hemoglobin is a protein!
• Binding events are both chemical and physical

120
Oxygen Transport

• Reverse occurs during unloading
• Release of one O2 induces shape change that
  speeds up the release of the next 3

121
Oxygen Transport

• More active metabolism (ie during muscle use)
  increases unloading
• Note steepness of curve
• O2 is unloaded quickly when metabolic use
  increases

Graph showing how hemoglobin oxygen saturation
changes with activity.
122
Oxygen Transport the Bohr Shift
Graph showing 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
123
Carbon Dioxide Transport
Figure showing how carbon dioxide is transported
from tissues to lungs. This figure is used in
the next 3 slides.

• Red blood cells also assist in CO2 transport
• 7 of CO2 is transported dissolved in plasma
• 23 is bound to amino groups of hemoglobin in the
  RBCs
• 70 is converted to bicarbonate ions inside the
  RBCs

124
Carbon Dioxide Transport

• CO2 in RBCs reacts with water to form carbonic
  acid (H2CO3)
• H2CO3 dissociates to bicarbonate (HCO3-) and H

125
Carbon Dioxide Transport

• Most H binds to hemoglobin
• This limits blood acidification
• HCO3- diffuses back into plasma for transport

126
Carbon Dioxide Transport

• Reverse occurs when blood reaches the lungs
• Conversion back to CO2 is driven by diffusion
  gradients as CO2 moves into the lungs

127
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