1. Circulation and Gas Exchange
Chapter 42
Circulation and Gas Exchange

2. Overview: Trading Places
Every organism must exchange materials with its environment
Exchanges ultimately occur at the cellular level by crossing the plasma membrane
In unicellular organisms, these exchanges occur directly with the environment
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3. Gills are an example of a specialized exchange system in animals
For most cells making up multicellular organisms, direct exchange with the environment is not possible
Gills are an example of a specialized exchange system in animals
O2 diffuses from the water into blood vessels
CO2 diffuses from blood into the water
Internal transport and gas exchange are functionally related in most animals
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4. Concept 42.1: Circulatory systems link exchange surfaces with cells throughout the body
Diffusion time is proportional to the square of the distance
Diffusion is only efficient over small distances
In small and/or thin animals, cells can exchange materials directly with the surrounding medium
In most animals, cells exchange materials with the environment via a fluid-filled circulatory system
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5. Gastrovascular Cavities
Some animals lack a circulatory system
Some cnidarians, such as jellies, have elaborate gastrovascular cavities
A gastrovascular cavity functions in both digestion and distribution of substances throughout the body
The body wall that encloses the gastrovascular cavity is only two cells thick
Flatworms have a gastrovascular cavity and a large surface area to volume ratio
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6. Evolutionary Variation in Circulatory Systems
A circulatory system minimizes the diffusion distance in animals with many cell layers
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7. General Properties of Circulatory Systems
A circulatory system has
A circulatory fluid
A set of interconnecting vessels
A muscular pump, the heart
The circulatory system connects the fluid that surrounds cells with the organs that exchange gases, absorb nutrients, and dispose of wastes
Circulatory systems can be open or closed, and vary in the number of circuits in the body
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8. Open and Closed Circulatory Systems
In insects, other arthropods, and most molluscs, blood bathes the organs directly in an open circulatory system
In an open circulatory system, there is no distinction between blood and interstitial fluid, and this general body fluid is called hemolymph
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9. (a) An open circulatory system (b) A closed circulatory system
Figure 42.3
(a) An open circulatory system
(b) A closed circulatory system
Heart
Heart
Interstitial fluid
Hemolymph in sinuses
surrounding organs
Blood
Small branch
vessels in
each organ
Pores
Dorsal
vessel
(main heart)
Auxiliary
hearts
Figure 42.3 Open and closed circulatory systems.
Tubular heart
Ventral vessels

10. Annelids, cephalopods, and vertebrates have closed circulatory systems
In a closed circulatory system, blood is confined to vessels and is distinct from the interstitial fluid
Closed systems are more efficient at transporting circulatory fluids to tissues and cells
Annelids, cephalopods, and vertebrates have closed circulatory systems
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11. Heart Dorsal vessel (main heart) Auxiliary hearts
Figure 42.3b
(b) A closed circulatory system
Heart
Interstitial fluid
Blood
Small branch
vessels in
each organ
Dorsal
vessel
(main heart)
Auxiliary
hearts
Figure 42.3 Open and closed circulatory systems.
Ventral vessels

12. Organization of Vertebrate Circulatory Systems
Humans and other vertebrates have a closed circulatory system called the cardiovascular system
The three main types of blood vessels are arteries, veins, and capillaries
Blood flow is one way in these vessels
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13. Arteries branch into arterioles and carry blood away from the heart to capillaries
Networks of capillaries called capillary beds are the sites of chemical exchange between the blood and interstitial fluid
Venules converge into veins and return blood from capillaries to the heart
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14. Vertebrate hearts contain two or more chambers
Arteries and veins are distinguished by the direction of blood flow, not by O2 content
Vertebrate hearts contain two or more chambers
Blood enters through an atrium and is pumped out through a ventricle
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15. Single Circulation
Bony fishes, rays, and sharks have single circulation with a two-chambered heart
In single circulation, blood leaving the heart passes through two capillary beds before returning
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16. (a) Single circulation (b) Double circulation
Figure 42.4
(a) Single circulation
(b) Double circulation
Pulmonary circuit
Gill
capillaries
Lung
capillaries
Artery
Heart: A A
Atrium (A) V V
Ventricle (V)
Right
Left
Vein
Figure 42.4 Single and double circulation in vertebrates.
Systemic
capillaries
Body
capillaries
Systemic circuit
Key
Oxygen-rich blood
Oxygen-poor blood

17. Double Circulation
Amphibian, reptiles, and mammals have double circulation
Oxygen-poor and oxygen-rich blood are pumped separately from the right and left sides of the heart
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18. (b) Double circulation
Figure 42.4b
(b) Double circulation
Pulmonary circuit
Lung
capillaries A A V V
Right
Left
Figure 42.4 Single and double circulation in vertebrates.
Systemic
capillaries
Systemic circuit
Key
Oxygen-rich blood
Oxygen-poor blood

19. Oxygen-rich blood delivers oxygen through the systemic circuit
In reptiles and mammals, oxygen-poor blood flows through the pulmonary circuit to pick up oxygen through the lungs
In amphibians, oxygen-poor blood flows through a pulmocutaneous circuit to pick up oxygen through the lungs and skin
Oxygen-rich blood delivers oxygen through the systemic circuit
Double circulation maintains higher blood pressure in the organs than does single circulation
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20. Adaptations of Double Circulatory Systems
Hearts vary in different vertebrate groups
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21. Amphibians
Frogs and other amphibians have a three-chambered heart: two atria and one ventricle
The ventricle pumps blood into a forked artery that splits the ventricle’s output into the pulmocutaneous circuit and the systemic circuit
When underwater, blood flow to the lungs is nearly shut off
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22. Amphibians Key Pulmocutaneous circuit Lung and skin capillaries Atrium
Figure 42.5a
Amphibians
Pulmocutaneous circuit
Lung
and skin
capillaries
Atrium
(A)
Atrium
(A)
Figure 42.5 Exploring: Double Circulation in Vertebrates
Right
Left
Ventricle (V)
Key
Systemic
capillaries
Oxygen-rich blood
Oxygen-poor blood
Systemic circuit

23. Reptiles (Except Birds)
Turtles, snakes, and lizards have a three-chambered heart: two atria and one ventricle
In alligators, caimans, and other crocodilians a septum divides the ventricle
Reptiles have double circulation, with a pulmonary circuit (lungs) and a systemic circuit
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24. Reptiles (Except Birds)
Figure 42.5b
Reptiles (Except Birds)
Pulmonary circuit
Lung
capillaries
Right
systemic
aorta
Left
systemic
aorta
Atrium
(A) A
Incomplete
septum V
Ventricle
(V)
Right
Left
Figure 42.5 Exploring: Double Circulation in Vertebrates
Key
Systemic
capillaries
Oxygen-rich blood
Oxygen-poor blood
Systemic circuit

25. Mammals and Birds
Mammals and birds have a four-chambered heart with two atria and two ventricles
The left side of the heart pumps and receives only oxygen-rich blood, while the right side receives and pumps only oxygen-poor blood
Mammals and birds are endotherms and require more O2 than ectotherms
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26. Mammals and Birds Pulmonary circuit Lung capillaries Atrium (A) A V
Figure 42.5c
Mammals and Birds
Pulmonary circuit
Lung
capillaries
Atrium
(A) A V
Ventricle
(V)
Right
Left
Figure 42.5 Exploring: Double Circulation in Vertebrates
Key
Systemic
capillaries
Oxygen-rich blood
Oxygen-poor blood
Systemic circuit

27. Pulmonary artery Aorta Pulmonary artery Right atrium Left atrium
Figure 42.7
Pulmonary artery
Aorta
Pulmonary
artery
Right
atrium
Left
atrium
Semilunar
valve
Semilunar
valve
Figure 42.7 The mammalian heart: a closer look.
Atrioventricular
valve
Atrioventricular
valve
Right
ventricle
Left
ventricle

28. Four valves prevent backflow of blood in the heart
The atrioventricular (AV) valves separate each atrium and ventricle
The semilunar valves control blood flow to the aorta and the pulmonary artery
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29. Backflow of blood through a defective valve causes a heart murmur
The “lub-dup” sound of a heart beat is caused by the recoil of blood against the AV valves (lub) then against the semilunar (dup) valves
Backflow of blood through a defective valve causes a heart murmur
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30. Fainting is caused by inadequate blood flow to the head
Animals with longer necks require a higher systolic pressure to pump blood a greater distance against gravity
Blood is moved through veins by smooth muscle contraction, skeletal muscle contraction, and expansion of the vena cava with inhalation
One-way valves in veins prevent backflow of blood
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31. Direction of blood flow in vein (toward heart) Valve (open)
Figure 42.13
Direction of blood flow
in vein (toward heart)
Valve (open)
Skeletal muscle
Figure Blood flow in veins.
Valve (closed)

32. Fluid Return by the Lymphatic System
The lymphatic system returns fluid that leaks out from the capillary beds
Fluid, called lymph, reenters the circulation directly at the venous end of the capillary bed and indirectly through the lymphatic system
The lymphatic system drains into veins in the neck
Valves in lymph vessels prevent the backflow of fluid
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33. Edema is swelling caused by disruptions in the flow of lymph
Lymph nodes are organs that filter lymph and play an important role in the body’s defense
Edema is swelling caused by disruptions in the flow of lymph
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34. Concept 42.4: Blood components contribute to exchange, transport, and defense
With open circulation, the fluid that is pumped comes into direct contact with all cells
The closed circulatory systems of vertebrates contain blood, a specialized connective tissue
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35. Blood Composition and Function
Blood consists of several kinds of cells suspended in a liquid matrix called plasma
The cellular elements occupy about 45% of the volume of blood
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36. Plasma Blood plasma is about 90% water
Among its solutes are inorganic salts in the form of dissolved ions, sometimes called electrolytes
Another important class of solutes is the plasma proteins, which influence blood pH, osmotic pressure, and viscosity
Various plasma proteins function in lipid transport, immunity, and blood clotting
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37. Cellular Elements Suspended in blood plasma are two types of cells
Red blood cells (erythrocytes) transport oxygen O2
White blood cells (leukocytes) function in defense
Platelets, a third cellular element, are fragments of cells that are involved in clotting
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38. Erythrocytes
Red blood cells, or erythrocytes, are by far the most numerous blood cells
They contain hemoglobin, the iron-containing protein that transports O2
Each molecule of hemoglobin binds up to four molecules of O2
In mammals, mature erythrocytes lack nuclei and mitochondria
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39. Leukocytes
There are five major types of white blood cells, or leukocytes: monocytes, neutrophils, basophils, eosinophils, and lymphocytes
They function in defense by phagocytizing bacteria and debris or by producing antibodies
They are found both in and outside of the circulatory system
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40. Platelets
Platelets are fragments of cells and function in blood clotting
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41. Blood Clotting
Coagulation is the formation of a solid clot from liquid blood
A cascade of complex reactions converts inactive fibrinogen to fibrin, forming a clot
A blood clot formed within a blood vessel is called a thrombus and can block blood flow
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42. Concept 42.5: Gas exchange occurs across specialized respiratory surfaces
Gas exchange supplies O2 for cellular respiration and disposes of CO2
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43. Partial Pressure Gradients in Gas Exchange
A gas diffuses from a region of higher partial pressure to a region of lower partial pressure
Partial pressure is the pressure exerted by a particular gas in a mixture of gases
Gases diffuse down pressure gradients in the lungs and other organs as a result of differences in partial pressure
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44. Respiratory Media
Animals can use air or water as a source of O2, or respiratory medium
In a given volume, there is less O2 available in water than in air
Obtaining O2 from water requires greater efficiency than air breathing
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45. Respiratory Surfaces
Animals require large, moist respiratory surfaces for exchange of gases between their cells and the respiratory medium, either air or water
Gas exchange across respiratory surfaces takes place by diffusion
Respiratory surfaces vary by animal and can include the outer surface, skin, gills, tracheae, and lungs
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46. Gills in Aquatic Animals
Gills are outfoldings of the body that create a large surface area for gas exchange
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47. Parapodium (functions as gill)
Figure 42.22a
Figure Diversity in the structure of gills, external body surfaces that function in gas exchange.
Parapodium (functions as gill)
(a) Marine worm

48. Gills (b) Crayfish Figure 42.22b
Figure Diversity in the structure of gills, external body surfaces that function in gas exchange.
Gills
(b) Crayfish

49. Coelom Gills Tube foot (c) Sea star Figure 42.22c
Figure Diversity in the structure of gills, external body surfaces that function in gas exchange.
Gills
Tube foot
(c) Sea star

50. Ventilation moves the respiratory medium over the respiratory surface
Aquatic animals move through water or move water over their gills for ventilation
Fish gills use a countercurrent exchange system, where blood flows in the opposite direction to water passing over the gills; blood is always less saturated with O2 than the water it meets
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51. Countercurrent exchange PO (mm Hg) in water 2
Figure 42.23
O2-poor blood
Gill
arch
O2-rich blood
Lamella
Blood
vessels
Gill arch
Water
flow
Operculum
Water flow
Blood flow
Countercurrent exchange
Figure The structure and function of fish gills.
PO (mm Hg) in water 2
150
120 90 60 30
Gill filaments
Net diffu-
sion of O2
140
110 80 50 20
PO (mm Hg)
in blood 2

52. Gill arch Blood vessels Gill arch Water flow Operculum Gill filaments
Figure 42.23a
Gill
arch
Blood
vessels
Gill arch
Water
flow
Operculum
Figure The structure and function of fish gills.
Gill filaments

53. Countercurrent exchange PO (mm Hg) in water
Figure 42.23b
O2-poor blood
O2-rich blood
Lamella
Water flow
Blood flow
Figure The structure and function of fish gills.
Countercurrent exchange
PO (mm Hg) in water 2
150
120 90 60 30
Net diffu-
sion of O2
140
110 80 50 20
PO (mm Hg)
in blood 2

54. Tracheal Systems in Insects
The tracheal system of insects consists of tiny branching tubes that penetrate the body
The tracheal tubes supply O2 directly to body cells
The respiratory and circulatory systems are separate
Larger insects must ventilate their tracheal system to meet O2 demands
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55. Tracheoles Mitochondria Muscle fiber 2.5 m Body cell Tracheae Air sac
Figure 42.24
Tracheoles
Mitochondria
Muscle fiber
2.5 m
Body
cell
Tracheae
Air
sac
Tracheole
Figure Tracheal systems.
Air sacs
Trachea
Air
External opening

56. Tracheoles Mitochondria Muscle fiber 2.5 m Figure 42.24a
Figure Tracheal systems.
2.5 m

57. Lungs Lungs are an infolding of the body surface
The circulatory system (open or closed) transports gases between the lungs and the rest of the body
The size and complexity of lungs correlate with an animal’s metabolic rate
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58. Mammalian Respiratory Systems: A Closer Look
A system of branching ducts conveys air to the lungs
Air inhaled through the nostrils is warmed, humidified, and sampled for odors
The pharynx directs air to the lungs and food to the stomach
Swallowing tips the epiglottis over the glottis in the pharynx to prevent food from entering the trachea
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59. enveloping alveoli (SEM)
Figure 42.25
Branch of
pulmonary vein
(oxygen-rich
blood)
Branch of
pulmonary artery
(oxygen-poor
blood)
Terminal
bronchiole
Nasal
cavity
Pharynx
Left
lung
Larynx
(Esophagus)
Alveoli
Trachea
50 m
Right lung
Capillaries
Bronchus
Figure The mammalian respiratory system.
Bronchiole
Diaphragm
(Heart)
Dense capillary bed
enveloping alveoli (SEM)

60. Nasal cavity Pharynx Left Larynx lung (Esophagus) Trachea Right lung
Figure 42.25a
Nasal
cavity
Pharynx
Left
lung
Larynx
(Esophagus)
Trachea
Right lung
Figure The mammalian respiratory system.
Bronchus
Bronchiole
Diaphragm
(Heart)

61. Branch of pulmonary vein (oxygen-rich blood) Branch of
Figure 42.25b
Branch of
pulmonary vein
(oxygen-rich
blood)
Branch of
pulmonary artery
(oxygen-poor
blood)
Terminal
bronchiole
Figure The mammalian respiratory system.
Alveoli
Capillaries

62. enveloping alveoli (SEM)
Figure 42.25c
50 m
Figure The mammalian respiratory system.
Dense capillary bed
enveloping alveoli (SEM)

63. Exhaled air passes over the vocal cords in the larynx to create sounds
Air passes through the pharynx, larynx, trachea, bronchi, and bronchioles to the alveoli, where gas exchange occurs
Exhaled air passes over the vocal cords in the larynx to create sounds
Cilia and mucus line the epithelium of the air ducts and move particles up to the pharynx
This “mucus escalator” cleans the respiratory system and allows particles to be swallowed into the esophagus
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64. Concept 42.6: Breathing ventilates the lungs
The process that ventilates the lungs is breathing, the alternate inhalation and exhalation of air
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65. How an Amphibian Breathes
An amphibian such as a frog ventilates its lungs by positive pressure breathing, which forces air down the trachea
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66. How a Bird Breathes
Birds have eight or nine air sacs that function as bellows that keep air flowing through the lungs
Air passes through the lungs in one direction only
Every exhalation completely renews the air in the lungs
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67. Anterior air sacs Posterior air sacs Airflow Air tubes (parabronchi)
Figure 42.27
Anterior
air sacs
Posterior
air sacs
Lungs
Airflow
Air tubes
(parabronchi)
in lung
1 mm
Lungs
Posterior
air sacs
Anterior
air sacs 3
Figure The avian respiratory system. 2 4 1 1
First inhalation 3
Second inhalation 2
First exhalation 4
Second exhalation

68. Airflow Air tubes (parabronchi) in lung 1 mm Figure 42.27a
Figure The avian respiratory system.
1 mm

69. How a Mammal Breathes
Mammals ventilate their lungs by negative pressure breathing, which pulls air into the lungs
Lung volume increases as the rib muscles and diaphragm contract
The tidal volume is the volume of air inhaled with each breath
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70. 1 2 Rib cage expands. Air inhaled. Rib cage gets smaller. Air exhaled.
Figure 42.28 1 2
Rib cage
expands.
Air
inhaled.
Rib cage gets
smaller.
Air
exhaled.
Lung
Figure Negative pressure breathing.
Diaphragm

71. Concept 42.7: Adaptations for gas exchange include pigments that bind and transport gases
The metabolic demands of many organisms require that the blood transport large quantities of O2 and CO2
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72. Coordination of Circulation and Gas Exchange
Blood arriving in the lungs has a low partial pressure of O2 and a high partial pressure of CO2 relative to air in the alveoli
In the alveoli, O2 diffuses into the blood and CO2 diffuses into the air
In tissue capillaries, partial pressure gradients favor diffusion of O2 into the interstitial fluids and CO2 into the blood
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73. Respiratory Adaptations of Diving Mammals
Diving mammals have evolutionary adaptations that allow them to perform extraordinary feats
For example, Weddell seals in Antarctica can remain underwater for 20 minutes to an hour
For example, elephant seals can dive to 1,500 m and remain underwater for 2 hours
These animals have a high blood to body volume ratio
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74. Deep-diving air breathers stockpile O2 and deplete it slowly
Diving mammals can store oxygen in their muscles in myoglobin proteins
Diving mammals also conserve oxygen by
Changing their buoyancy to glide passively
Decreasing blood supply to muscles
Deriving ATP in muscles from fermentation once oxygen is depleted
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