Chapter 22 Gas Exchange.

Chapter 22 Gas Exchange

Introduction People cannot survive for long in the air at the world’s highest peaks in the Himalayan Mountains. Yet twice a year, flocks of geese migrate over the Himalayas. How can geese fly where people cannot breathe? Geese have more efficient lungs than humans, and their hemoglobin has a very high affinity for oxygen. © 2012 Pearson Education, Inc. 2

Mechanisms of Gas Exchange The Human Respiratory System
Figure 22.0_1 Chapter 22: Big Ideas Mechanisms of Gas Exchange The Human Respiratory System Figure 22.0_1 Chapter 22: Big ideas Transport of Gases in the Human Body 3

Figure 22.0_2 Figure 22.0_2 Migrating geese 4

MECHANISMS OF GAS EXCHANGE
MECHANISMS OF GAS EXCHANGE © 2012 Pearson Education, Inc. 5

22.1 Overview: Gas exchange in humans involves breathing, transport of gases, and exchange with body cells The process of gas exchange is sometimes called respiration, the interchange of O2 and the waste product CO2 between an organism and its environment. Student Misconceptions and Concerns 1. As the authors note (in Module 22.1), it is important to distinguish between the use of the word respiration in the context of the whole organism (breathing) and in the context of cells (cellular respiration). 2. Respiratory structures such as gills, lungs, and insect tracheal systems are highly branched, reflecting an adaptation to increase the surface area and ultimately the surface-to-volume ratio of the animal. Students might not realize the common principles of adaptations to increase surface-to-volume ratios in the highly branched respiratory structures, as well as in the circulatory system (for example, the small size of red blood cells and tiny size of capillaries), discussed in detail in the next chapter. You might consider expanding on this principle as you address other systems that reflect such adaptations (for example, greater surface area of the digestive system for absorption of nutrients). Teaching Tips You may want to point out that in scientific artwork, it is common to identify blood vessels in the arterial system by coloring them red, and blood vessels in the venous system by coloring them blue. As experienced biologists, such expectations can be so routine that we forget that we might need to point this out to our students. © 2012 Pearson Education, Inc. 6

22.1 Overview: Gas exchange in humans involves breathing, transport of gases, and exchange with body cells Three phases of gas exchange occur in humans and other animals with lungs: breathing, transport of oxygen and carbon dioxide in blood, and exchange of gases with body cells. Body tissues take up oxygen and release carbon dioxide. Cellular respiration requires a continuous supply of oxygen and the disposal of carbon dioxide. Student Misconceptions and Concerns 1. As the authors note (in Module 22.1), it is important to distinguish between the use of the word respiration in the context of the whole organism (breathing) and in the context of cells (cellular respiration). 2. Respiratory structures such as gills, lungs, and insect tracheal systems are highly branched, reflecting an adaptation to increase the surface area and ultimately the surface-to-volume ratio of the animal. Students might not realize the common principles of adaptations to increase surface-to-volume ratios in the highly branched respiratory structures, as well as in the circulatory system (for example, the small size of red blood cells and tiny size of capillaries), discussed in detail in the next chapter. You might consider expanding on this principle as you address other systems that reflect such adaptations (for example, greater surface area of the digestive system for absorption of nutrients). Teaching Tips You may want to point out that in scientific artwork, it is common to identify blood vessels in the arterial system by coloring them red, and blood vessels in the venous system by coloring them blue. As experienced biologists, such expectations can be so routine that we forget that we might need to point this out to our students. © 2012 Pearson Education, Inc. 7

Transport of gases by the circulatory system
Figure 22.1 O2 1 Breathing CO2 Lung Heart Circulatory System Blood vessels 2 Transport of gases by the circulatory system Figure 22.1 The three phases of gas exchange in a human Capillary Mitochondria Exchange of gases with body cells O2 3 CO2 Cell 8

22.2 Animals exchange O2 and CO2 across moist body surfaces
Respiratory surfaces must be moist for diffusion of O2 and CO2 and thin, to best facilitate diffusion. The skin may be used for gas exchange in animals that are wet and small. Earthworms are an example. Student Misconceptions and Concerns Respiratory structures such as gills, lungs, and insect tracheal systems are highly branched, reflecting an adaptation to increase the surface area and ultimately the surface-to-volume ratio of the animal. Students might not realize the common principles of adaptations to increase surface-to-volume ratios in the highly branched respiratory structures, as well as in the circulatory system (for example, the small size of red blood cells and tiny size of capillaries), discussed in detail in the next chapter. You might consider expanding on this principle as you address other systems that reflect such adaptations (for example, greater surface area of the digestive system for absorption of nutrients). Teaching Tips Salamanders in the family Plethodontidae are unusual terrestrial vertebrates that survive mainly on land as adults, yet have no lungs. The adults acquire all of their oxygen through their skin. Consider discussing with your class how this is possible. Their relatively small size, slow metabolic rates, preference for cool environments, and minimal physical activity all permit the absence of lungs. © 2012 Pearson Education, Inc. 9

Cross section of the respiratory surface (the outer skin)
Figure 22.2A Cross section of the respiratory surface (the outer skin) CO2 Figure 22.2A The skin: the outer body surface O2 Capillaries 10

22.2 Animals exchange O2 and CO2 across moist body surfaces
Most animals have specialized body parts that promote gas exchange: gills in fish and amphibians, tracheal systems in arthropods, and lungs in tetrapods that live on land, such as amphibians, reptiles including birds, and mammals. Student Misconceptions and Concerns Respiratory structures such as gills, lungs, and insect tracheal systems are highly branched, reflecting an adaptation to increase the surface area and ultimately the surface-to-volume ratio of the animal. Students might not realize the common principles of adaptations to increase surface-to-volume ratios in the highly branched respiratory structures, as well as in the circulatory system (for example, the small size of red blood cells and tiny size of capillaries), discussed in detail in the next chapter. You might consider expanding on this principle as you address other systems that reflect such adaptations (for example, greater surface area of the digestive system for absorption of nutrients). Teaching Tips Salamanders in the family Plethodontidae are unusual terrestrial vertebrates that survive mainly on land as adults, yet have no lungs. The adults acquire all of their oxygen through their skin. Consider discussing with your class how this is possible. Their relatively small size, slow metabolic rates, preference for cool environments, and minimal physical activity all permit the absence of lungs. © 2012 Pearson Education, Inc. 11

Respiratory surface (gills)
Figure 22.2B Body surface Respiratory surface (gills) Figure 22.2B Gills: extensions of the body surface CO2 O2 Capillary 12

Body cells (no capillaries)
Figure 22.2C Body surface Respiratory surface (tips of tracheae) O2 Figure 22.2C A tracheal system: air tubes that extend throughout the body Body cells (no capillaries) CO2 13

Respiratory surface (within lung) CO2 O2
Figure 22.2D Body surface Respiratory surface (within lung) CO2 O2 Figure 22.2D Lungs: internal thin-walled sacs CO2 O2 Capillary 14

22.3 Gills are adapted for gas exchange in aquatic environments
Gills are extensions of the body, increase the surface to volume ratio, and increase the surface area for gas exchange. Oxygen is absorbed. Carbon dioxide is released. Student Misconceptions and Concerns Respiratory structures such as gills, lungs, and insect tracheal systems are highly branched, reflecting an adaptation to increase the surface area and ultimately the surface-to-volume ratio of the animal. Students might not realize the common principles of adaptations to increase surface-to-volume ratios in the highly branched respiratory structures, as well as in the circulatory system (for example, the small size of red blood cells and tiny size of capillaries), discussed in detail in the next chapter. You might consider expanding on this principle as you address other systems that reflect such adaptations (for example, greater surface area of the digestive system for absorption of nutrients). Teaching Tips 1. Students struggling to recall the conditions that increase the oxygen content of water might benefit by picturing in their mind a scenario that includes all the best conditions. A pool at the base of a waterfall, generated from melting snow, has a very high oxygen content because the water is (a) fresh, (b) cool, and (c) turbulent. 2. As the authors note in Module 22.3, the basic principles of countercurrent exchange apply to the transfer of gases and temperature. Countercurrent exchange as it applies to temperature is addressed in Chapter 25. 3. Challenge your class to explain why fish gills do not work well in air. As noted in Modules 22.2 and 22.3, respiratory surfaces need to remain moist. In addition, the surface area of the gills is greatly reduced as the filaments adhere to each other. You can visually demonstrate this point by simply lifting your hand and spreading your fingers apart, noting that gills are spaced like this in water. In air (bring your fingers together), the filaments adhere into one larger mass with less surface area. © 2012 Pearson Education, Inc. 15

In a fish, gas exchange is enhanced by ventilation of the gills (moving water past the gills) and countercurrent flow of water and blood. Student Misconceptions and Concerns Respiratory structures such as gills, lungs, and insect tracheal systems are highly branched, reflecting an adaptation to increase the surface area and ultimately the surface-to-volume ratio of the animal. Students might not realize the common principles of adaptations to increase surface-to-volume ratios in the highly branched respiratory structures, as well as in the circulatory system (for example, the small size of red blood cells and tiny size of capillaries), discussed in detail in the next chapter. You might consider expanding on this principle as you address other systems that reflect such adaptations (for example, greater surface area of the digestive system for absorption of nutrients). Teaching Tips 1. Students struggling to recall the conditions that increase the oxygen content of water might benefit by picturing in their mind a scenario that includes all the best conditions. A pool at the base of a waterfall, generated from melting snow, has a very high oxygen content because the water is (a) fresh, (b) cool, and (c) turbulent. 2. As the authors note in Module 22.3, the basic principles of countercurrent exchange apply to the transfer of gases and temperature. Countercurrent exchange as it applies to temperature is addressed in Chapter 25. 3. Challenge your class to explain why fish gills do not work well in air. As noted in Modules 22.2 and 22.3, respiratory surfaces need to remain moist. In addition, the surface area of the gills is greatly reduced as the filaments adhere to each other. You can visually demonstrate this point by simply lifting your hand and spreading your fingers apart, noting that gills are spaced like this in water. In air (bring your fingers together), the filaments adhere into one larger mass with less surface area. © 2012 Pearson Education, Inc. 16

Gas exchange with water has its limits. Water holds only about 3% of the oxygen in air. Cold water holds more oxygen than warm water. Fresh water holds more oxygen than salt water. Turbulent water holds more oxygen than still water. Student Misconceptions and Concerns Respiratory structures such as gills, lungs, and insect tracheal systems are highly branched, reflecting an adaptation to increase the surface area and ultimately the surface-to-volume ratio of the animal. Students might not realize the common principles of adaptations to increase surface-to-volume ratios in the highly branched respiratory structures, as well as in the circulatory system (for example, the small size of red blood cells and tiny size of capillaries), discussed in detail in the next chapter. You might consider expanding on this principle as you address other systems that reflect such adaptations (for example, greater surface area of the digestive system for absorption of nutrients). Teaching Tips 1. Students struggling to recall the conditions that increase the oxygen content of water might benefit by picturing in their mind a scenario that includes all the best conditions. A pool at the base of a waterfall, generated from melting snow, has a very high oxygen content because the water is (a) fresh, (b) cool, and (c) turbulent. 2. As the authors note in Module 22.3, the basic principles of countercurrent exchange apply to the transfer of gases and temperature. Countercurrent exchange as it applies to temperature is addressed in Chapter 25. 3. Challenge your class to explain why fish gills do not work well in air. As noted in Modules 22.2 and 22.3, respiratory surfaces need to remain moist. In addition, the surface area of the gills is greatly reduced as the filaments adhere to each other. You can visually demonstrate this point by simply lifting your hand and spreading your fingers apart, noting that gills are spaced like this in water. In air (bring your fingers together), the filaments adhere into one larger mass with less surface area. © 2012 Pearson Education, Inc. 17

Blood flow in simplified
Figure 22.3 Oxygen-poor blood Oxygen-rich blood Lamella Water flow Blood vessels Operculum (gill cover) Gill arch Water flow between lamellae Blood flow through capillaries in a lamella Figure 22.3 The structure of fish gills and countercurrent gas exchange Countercurrent exchange Water flow, showing % O2 Gill filaments Diffusion of O2 from water to blood Blood flow in simplified capillary, showing % O2 18

Operculum (gill cover)
Figure 22.3_1 Water flow Blood vessels Operculum (gill cover) Gill arch Figure 22.3_1 The structure of fish gills and countercurrent gas exchange (part 1) Gill filaments 19

Blood flow in simplified capillary, showing % O2
Figure 22.3_2 Oxygen-poor blood Oxygen- rich blood Lamella Countercurrent exchange Water flow, showing % O2 Diffusion of O2 from water to blood Blood flow in simplified capillary, showing % O2 Water flow between lamellae Figure 22.3_2 The structure of fish gills and countercurrent gas exchange (part 2) Blood flow through capillaries in a lamella 20

22.4 The tracheal system of insects provides direct exchange between the air and body cells
Compared to water, using air to breathe has two big advantages. Air contains higher concentrations of O2 than water. Air is lighter and easier to move than water. However, air-breathing animals lose water through their respiratory surfaces. Student Misconceptions and Concerns Respiratory structures such as gills, lungs, and insect tracheal systems are highly branched, reflecting an adaptation to increase the surface area and ultimately the surface-to-volume ratio of the animal. Students might not realize the common principles of adaptations to increase surface-to-volume ratios in the highly branched respiratory structures, as well as in the circulatory system (for example, the small size of red blood cells and tiny size of capillaries), discussed in detail in the next chapter. You might consider expanding on this principle as you address other systems that reflect such adaptations (for example, greater surface area of the digestive system for absorption of nutrients). Teaching Tips 1. You might mention to your class that most animals use tracheal systems. After all, insects are by far the dominant type of animal on Earth (at least 70% of all known animal species). Therefore, whatever insects do is automatically the most common animal adaptation! 2. In a very general sense, the tracheal system of insects is like the ductwork bringing outside air into the individual offices of a high-rise building. (But unlike a tracheal system, the air is removed from the building by another system.) © 2012 Pearson Education, Inc. 21

22.4 The tracheal system of insects provides direct exchange between the air and body cells
Insect tracheal systems use tiny branching tubes that reduce water loss and pipe air directly to cells. Student Misconceptions and Concerns Respiratory structures such as gills, lungs, and insect tracheal systems are highly branched, reflecting an adaptation to increase the surface area and ultimately the surface-to-volume ratio of the animal. Students might not realize the common principles of adaptations to increase surface-to-volume ratios in the highly branched respiratory structures, as well as in the circulatory system (for example, the small size of red blood cells and tiny size of capillaries), discussed in detail in the next chapter. You might consider expanding on this principle as you address other systems that reflect such adaptations (for example, greater surface area of the digestive system for absorption of nutrients). Teaching Tips 1. You might mention to your class that most animals use tracheal systems. After all, insects are by far the dominant type of animal on Earth (at least 70% of all known animal species). Therefore, whatever insects do is automatically the most common animal adaptation! 2. In a very general sense, the tracheal system of insects is like the ductwork bringing outside air into the individual offices of a high-rise building. (But unlike a tracheal system, the air is removed from the building by another system.) © 2012 Pearson Education, Inc. 22

Tracheae Air sacs Tracheoles Opening for air Body cell Air sac
Figure 22.4A Tracheae Air sacs Tracheoles Opening for air Body cell Air sac Tracheole Figure 22.4A The tracheal system of an insect Trachea Body wall O2 CO2 23

Figure 22.4A_1 Tracheoles Figure 22.4A_1 The tracheal system of an insect (micrograph) 24

Figure 22.4B Figure 22.4B A grasshopper in flight 25

22.5 EVOLUTION CONNECTION:The evolution of lungs facilitated the movement of tetrapods onto land
Tetrapods seem to have evolved in shallow water. Fossil fish with legs had lungs and gills. Legs may have helped them lift up to gulp air. The fossil fish Tiktaalik lived about 375 million years ago and illustrates these air-breathing adaptations. Student Misconceptions and Concerns Respiratory structures such as gills, lungs, and insect tracheal systems are highly branched, reflecting an adaptation to increase the surface area and ultimately the surface-to-volume ratio of the animal. Students might not realize the common principles of adaptations to increase surface-to-volume ratios in the highly branched respiratory structures, as well as in the circulatory system (for example, the small size of red blood cells and tiny size of capillaries), discussed in detail in the next chapter. You might consider expanding on this principle as you address other systems that reflect such adaptations (for example, greater surface area of the digestive system for absorption of nutrients). Teaching Tips Many aquatic amphibians, such as the axolotl salamander, use gills, lungs, and skin surfaces for gas exchange. As noted in Module 22.5, this appears to be true of the first tetrapods such as Tiktaalik. © 2012 Pearson Education, Inc. 26

Eyes on top of a flat skull
Figure 22.5 Shoulder bones Neck Eyes on top of a flat skull Figure 22.5 A cast of a fossil of Tiktaalik Fin 27

22.5 CONNECTION:The evolution of lungs facilitated the movement of tetrapods onto land
The first tetrapods on land diverged into three major lineages. Amphibians use small lungs and their body surfaces. Nonbird reptiles have lower metabolic rates and simpler lungs. Birds and mammals have higher metabolic rates and more complex lungs. Student Misconceptions and Concerns Respiratory structures such as gills, lungs, and insect tracheal systems are highly branched, reflecting an adaptation to increase the surface area and ultimately the surface-to-volume ratio of the animal. Students might not realize the common principles of adaptations to increase surface-to-volume ratios in the highly branched respiratory structures, as well as in the circulatory system (for example, the small size of red blood cells and tiny size of capillaries), discussed in detail in the next chapter. You might consider expanding on this principle as you address other systems that reflect such adaptations (for example, greater surface area of the digestive system for absorption of nutrients). Teaching Tips Many aquatic amphibians, such as the axolotl salamander, use gills, lungs, and skin surfaces for gas exchange. As noted in Module 22.5, this appears to be true of the first tetrapods such as Tiktaalik. © 2012 Pearson Education, Inc. 28

THE HUMAN RESPIRATORY SYSTEM
THE HUMAN RESPIRATORY SYSTEM © 2012 Pearson Education, Inc. 29

22.6 In mammals, branching tubes convey air to lungs located in the chest cavity
The diaphragm separates the abdominal cavity from the thoracic cavity and helps ventilate the lungs. In mammals, air is inhaled through the nostrils into the nasal cavity. Air is filtered by hairs and mucus surfaces, warmed and humidified, and sampled for odors. Student Misconceptions and Concerns Students often confuse the structures and functions of the trachea and esophagus. To help them distinguish, point out that the trachea has a structure and function like the hose of a vacuum cleaner. The rigid ribbed walls of the trachea keep the tube open as air is sucked through it. The esophagus, however, relies upon rhythmic changes in the shape of the walls (peristalsis) to push food toward the stomach. If the esophagus had stiff walls, it would not be able to perform this function. Teaching Tips 1. The basic principles of the vocal cords can be demonstrated by inflating a balloon and letting air out, while stretching the neck of the balloon. If the balloon neck is stretched tightly, it will produce high-pitched sounds; when it is relaxed, it will produce lower-pitched sounds. 2. Students often appreciate explanations that help them understand their own experiences. When we struggle with respiratory infections or allergies, especially when the air is dry, thick mucus accumulates in our branchial system. A long, warm shower hydrates these mucus films, facilitating their movement up and out of our respiratory systems. Although students might have heard this advice, they might not have fully understood the mechanisms. (Sipping hot tea also helps to hydrate these mucus surfaces.) © 2012 Pearson Education, Inc. 30

From the nasal cavity, air next passes to the pharynx, then larynx, past the vocal cords, into the trachea, held open by cartilage rings, into the paired bronchi, into bronchioles, and finally to the alveoli, grapelike clusters of air sacs, where gas exchange occurs. Student Misconceptions and Concerns Students often confuse the structures and functions of the trachea and esophagus. To help them distinguish, point out that the trachea has a structure and function like the hose of a vacuum cleaner. The rigid ribbed walls of the trachea keep the tube open as air is sucked through it. The esophagus, however, relies upon rhythmic changes in the shape of the walls (peristalsis) to push food toward the stomach. If the esophagus had stiff walls, it would not be able to perform this function. Teaching Tips 1. The basic principles of the vocal cords can be demonstrated by inflating a balloon and letting air out, while stretching the neck of the balloon. If the balloon neck is stretched tightly, it will produce high-pitched sounds; when it is relaxed, it will produce lower-pitched sounds. 2. Students often appreciate explanations that help them understand their own experiences. When we struggle with respiratory infections or allergies, especially when the air is dry, thick mucus accumulates in our branchial system. A long, warm shower hydrates these mucus films, facilitating their movement up and out of our respiratory systems. Although students might have heard this advice, they might not have fully understood the mechanisms. (Sipping hot tea also helps to hydrate these mucus surfaces.) © 2012 Pearson Education, Inc. 31

Figure 22.6A To the heart From the heart Nasal cavity Oxygen-rich blood Left lung Oxygen-poor blood Pharynx (Esophagus) Bronchiole Larynx Trachea Right lung CO2 O2 Bronchus Bronchiole Figure 22.6A The anatomy of the human respiratory system (left) and details of the alveoli (right) Alveoli Diaphragm Blood capillaries (Heart) 32

Nasal cavity Left lung Pharynx (Esophagus) Larynx Trachea Right lung
Figure 22.6A_1 Nasal cavity Left lung Pharynx (Esophagus) Larynx Trachea Right lung Bronchus Figure 22.6A_1 The anatomy of the human respiratory system and details of the alveoli (part 1) Bronchiole Diaphragm (Heart) 33

To the heart From the heart
Figure 22.6A_2 To the heart From the heart Oxygen-rich blood Oxygen-poor blood Bronchiole CO2 O2 Figure 22.6A_2 The anatomy of the human respiratory system and details of the alveoli (part 2) Alveoli Blood capillaries 34

Alveoli are well adapted for gas exchange with high surface areas of capillaries. In alveoli, O2 diffuses into the blood and CO2 diffuses out of the blood. Student Misconceptions and Concerns Students often confuse the structures and functions of the trachea and esophagus. To help them distinguish, point out that the trachea has a structure and function like the hose of a vacuum cleaner. The rigid ribbed walls of the trachea keep the tube open as air is sucked through it. The esophagus, however, relies upon rhythmic changes in the shape of the walls (peristalsis) to push food toward the stomach. If the esophagus had stiff walls, it would not be able to perform this function. Teaching Tips 1. The basic principles of the vocal cords can be demonstrated by inflating a balloon and letting air out, while stretching the neck of the balloon. If the balloon neck is stretched tightly, it will produce high-pitched sounds; when it is relaxed, it will produce lower-pitched sounds. 2. Students often appreciate explanations that help them understand their own experiences. When we struggle with respiratory infections or allergies, especially when the air is dry, thick mucus accumulates in our branchial system. A long, warm shower hydrates these mucus films, facilitating their movement up and out of our respiratory systems. Although students might have heard this advice, they might not have fully understood the mechanisms. (Sipping hot tea also helps to hydrate these mucus surfaces.) © 2012 Pearson Education, Inc. 35

Figure 22.6B Figure 22.6B A colorized electron micrograph showing the network of capillaries that surround the alveoli in the lung 36

Surfactants are specialized secretions required to keep the walls of the small alveoli from sticking shut. Babies born 6 weeks or more before their due date often struggle with respiratory distress syndrome due to an inadequate amount of lung surfactant. Artificial surfactants are now administered to preterm infants. Student Misconceptions and Concerns Students often confuse the structures and functions of the trachea and esophagus. To help them distinguish, point out that the trachea has a structure and function like the hose of a vacuum cleaner. The rigid ribbed walls of the trachea keep the tube open as air is sucked through it. The esophagus, however, relies upon rhythmic changes in the shape of the walls (peristalsis) to push food toward the stomach. If the esophagus had stiff walls, it would not be able to perform this function. Teaching Tips 1. The basic principles of the vocal cords can be demonstrated by inflating a balloon and letting air out, while stretching the neck of the balloon. If the balloon neck is stretched tightly, it will produce high-pitched sounds; when it is relaxed, it will produce lower-pitched sounds. 2. Students often appreciate explanations that help them understand their own experiences. When we struggle with respiratory infections or allergies, especially when the air is dry, thick mucus accumulates in our branchial system. A long, warm shower hydrates these mucus films, facilitating their movement up and out of our respiratory systems. Although students might have heard this advice, they might not have fully understood the mechanisms. (Sipping hot tea also helps to hydrate these mucus surfaces.) © 2012 Pearson Education, Inc. 37

Exposure to pollutants can cause continual irritation and inflammation of the lungs. Examples of common lung pollutants include air pollution and tobacco smoke. Chronic obstructive pulmonary disease (COPD) can result, limiting lung ventilation and gas exchange. Student Misconceptions and Concerns Students often confuse the structures and functions of the trachea and esophagus. To help them distinguish, point out that the trachea has a structure and function like the hose of a vacuum cleaner. The rigid ribbed walls of the trachea keep the tube open as air is sucked through it. The esophagus, however, relies upon rhythmic changes in the shape of the walls (peristalsis) to push food toward the stomach. If the esophagus had stiff walls, it would not be able to perform this function. Teaching Tips 1. The basic principles of the vocal cords can be demonstrated by inflating a balloon and letting air out, while stretching the neck of the balloon. If the balloon neck is stretched tightly, it will produce high-pitched sounds; when it is relaxed, it will produce lower-pitched sounds. 2. Students often appreciate explanations that help them understand their own experiences. When we struggle with respiratory infections or allergies, especially when the air is dry, thick mucus accumulates in our branchial system. A long, warm shower hydrates these mucus films, facilitating their movement up and out of our respiratory systems. Although students might have heard this advice, they might not have fully understood the mechanisms. (Sipping hot tea also helps to hydrate these mucus surfaces.) © 2012 Pearson Education, Inc. 38

22.7 CONNECTION: Smoking is a serious assault on the respiratory system
Mucus and cilia in the respiratory passages sweep contaminant-laden mucus up and out of the airways and can be damaged by smoking. One of the worst sources of lung-damaging air pollutants is tobacco smoke, containing more than 4,000 chemicals. Without healthy cilia, smokers must cough to clear dirty mucus from the trachea. Student Misconceptions and Concerns Students might misunderstand how the cilia lining our respiratory passages work. Cilia do not filter the air like a comb. Instead, cilia are covered by a layer of mucus. Dust particles adhere to sticky mucus, which is then swept up the respiratory tract by the cilia. If students clear their throats, they will identify the fate of this mucus. We swallow after clearing our throats! Teaching Tips The impact of smoking on public health is described in detail in Module Despite this increasingly available information, many students still choose to smoke. Consider including some exercise in your class that will provide students with an opportunity to better understand the public health consequences of smoking. © 2012 Pearson Education, Inc. 39

Smoking can cause lung cancer, cardiovascular disease, and emphysema. Smoking accounts for 90% of all lung cancer cases. Smoking increases the risk of other types of cancer. Student Misconceptions and Concerns Students might misunderstand how the cilia lining our respiratory passages work. Cilia do not filter the air like a comb. Instead, cilia are covered by a layer of mucus. Dust particles adhere to sticky mucus, which is then swept up the respiratory tract by the cilia. If students clear their throats, they will identify the fate of this mucus. We swallow after clearing our throats! Teaching Tips The impact of smoking on public health is described in detail in Module Despite this increasingly available information, many students still choose to smoke. Consider including some exercise in your class that will provide students with an opportunity to better understand the public health consequences of smoking. © 2012 Pearson Education, Inc. 40

Smoking also increases the risk of heart attacks and strokes, raises blood pressure, and increases harmful types of cholesterol. Every year in the United States, smoking kills about 440,000 people, more than all the deaths from accidents, alcohol, drug abuse, HIV, and murders combined. Adults who smoke die 13–14 years earlier than nonsmokers. Student Misconceptions and Concerns Students might misunderstand how the cilia lining our respiratory passages work. Cilia do not filter the air like a comb. Instead, cilia are covered by a layer of mucus. Dust particles adhere to sticky mucus, which is then swept up the respiratory tract by the cilia. If students clear their throats, they will identify the fate of this mucus. We swallow after clearing our throats! Teaching Tips The impact of smoking on public health is described in detail in Module Despite this increasingly available information, many students still choose to smoke. Consider including some exercise in your class that will provide students with an opportunity to better understand the public health consequences of smoking. © 2012 Pearson Education, Inc. 41

Figure 22.7 Lung Figure 22.7 Healthy lungs (left) and cancerous lungs (right) Heart 42

22.8 Negative pressure breathing ventilates your lungs
Breathing is the alternate inhalation and exhalation of air (ventilation). In mammals, inhalation occurs when the rib cage expands, the diaphragm moves downward, the pressure around the lungs decreases, and air is drawn into the respiratory tract. This type of ventilation is called negative pressure breathing. Teaching Tips 1. In its relaxed state, the human diaphragm is domed upward toward the heart. Contracting the diaphragm pushes down on the intestines and stomach, forcing the abdominal region outward. Thus, it can be more difficult to inhale after having consumed a large volume of food and/or drink. 2. Some of your students may have been taught to breathe deeply by actively extending their stomach outwards. Ask your class to explain why this permits them to take a deeper breath. (The answer: it allows the diaphragm to move down with less resistance from body organs in the abdominal cavity). © 2012 Pearson Education, Inc. 43

The diaphragm contracts (moves down) The diaphragm relaxes (moves up)
Figure 22.8 Rib cage expands as rib muscles contract Rib cage gets smaller as rib muscles relax Air inhaled Air exhaled Lung Diaphragm Figure 22.8 Negative pressure breathing The diaphragm contracts (moves down) The diaphragm relaxes (moves up) Inhalation Exhalation 44

Exhalation occurs when the rib cage contracts, the diaphragm moves upward, the pressure around the lungs increases, and air is forced out of the respiratory tract. Teaching Tips 1. In its relaxed state, the human diaphragm is domed upward toward the heart. Contracting the diaphragm pushes down on the intestines and stomach, forcing the abdominal region outward. Thus, it can be more difficult to inhale after having consumed a large volume of food and/or drink. 2. Some of your students may have been taught to breathe deeply by actively extending their stomach outwards. Ask your class to explain why this permits them to take a deeper breath. (The answer: it allows the diaphragm to move down with less resistance from body organs in the abdominal cavity). © 2012 Pearson Education, Inc. 45

Not all air is expelled during exhalation. Some air still remains in the trachea, bronchi, bronchioles, and alveoli. This remaining air is “dead air.” Thus, inhalation mixes fresh air with dead air. One-way flow of air in birds reduces dead air and increases their ability to obtain oxygen. Teaching Tips 1. In its relaxed state, the human diaphragm is domed upward toward the heart. Contracting the diaphragm pushes down on the intestines and stomach, forcing the abdominal region outward. Thus, it can be more difficult to inhale after having consumed a large volume of food and/or drink. 2. Some of your students may have been taught to breathe deeply by actively extending their stomach outwards. Ask your class to explain why this permits them to take a deeper breath. (The answer: it allows the diaphragm to move down with less resistance from body organs in the abdominal cavity). © 2012 Pearson Education, Inc. 46

22.9 Breathing is automatically controlled
Breathing is usually under automatic control. Breathing control centers in the brain sense and respond to CO2 levels in the blood. A drop in blood pH increases the rate and depth of breathing. Teaching Tips As noted in Module 22.9, the breathing control centers in the brain are based upon the concentration of carbon dioxide in the blood (and the resulting changes in pH). Challenge your students to explain why this system is usually sufficient to provide adequate levels of oxygen in the blood. (The by-product of aerobic respiration is carbon dioxide.) © 2012 Pearson Education, Inc. 47

Nerve signals trigger contraction of the rib muscles and diaphragm.
Figure 22.9_s1 Brain Cerebrospinal fluid 1 Nerve signals trigger contraction of the rib muscles and diaphragm. Medulla Figure 22.9_s1 How the breathing control center regulates breathing (step 1) Diaphragm Rib muscles 48

Figure 22.9_s2 Brain Cerebrospinal fluid 2 Breathing control center responds to the pH of blood and cerebrospinal fluid. 1 Nerve signals trigger contraction of the rib muscles and diaphragm. Medulla Figure 22.9_s2 How the breathing control center regulates breathing (step 2) Diaphragm Rib muscles 49

Figure 22.9_s3 Brain Cerebrospinal fluid 2 Breathing control center responds to the pH of blood and cerebrospinal fluid. 1 Nerve signals trigger contraction of the rib muscles and diaphragm. Medulla 3 Nerve signals indicate CO2 and O2 levels. Figure 22.9_s3 How the breathing control center regulates breathing (step 3) CO2 and O2 sensors in the aorta Heart Diaphragm Rib muscles 50

TRANSPORT OF GASES IN THE HUMAN BODY
TRANSPORT OF GASES IN THE HUMAN BODY © 2012 Pearson Education, Inc. 51

22.10 Blood transports respiratory gases
The heart pumps blood to two regions. The right side pumps oxygen-poor blood to the lungs. The left side pumps oxygen-rich blood to the body. In the lungs, blood picks up O2 and drops off CO2. In the body tissues, blood drops off O2 and picks up CO2. Student Misconceptions and Concerns 1. Many students still struggle with the concept of diffusion as the main mechanism of gas transport. Before discussing gas transport, ask your class to explain why oxygen moves out of the blood in body tissues, but into the blood in the lungs. Why don’t these processes proceed in the opposite direction? 2. Many students struggle with fundamental aspects of fetal circulation and respiration. Students might assume that the mother’s blood flows through the umbilical cord into the fetus. Students might also expect that the fetus is somehow breathing air. Nobody likes to be embarrassed by ignorance, so gauging these and many other misconceptions can be a challenge. To better understand your students’ background knowledge consider giving a short quiz on fundamental points before lecturing on the subject. Teaching Tips Figure is an especially helpful depiction of the movements of gases in the human respiratory system. The figure includes all of the main sites where oxygen is consumed, the alveoli where gas exchange occurs in the lungs, and the separate movement of oxygenated and deoxygenated blood through the heart. © 2012 Pearson Education, Inc. 52

A mixture of gases, such as air, exerts pressure. Each kind of gas in a mixture accounts for a portion of the total pressure of the mixture. Thus, each gas has a partial pressure. The exchange of gases between capillaries and the surrounding cells is based on partial pressures. Molecules of each kind of gas diffuse down a gradient of its own partial pressure, moving from regions of higher partial pressure to lower partial pressure. Student Misconceptions and Concerns 1. Many students still struggle with the concept of diffusion as the main mechanism of gas transport. Before discussing gas transport, ask your class to explain why oxygen moves out of the blood in body tissues, but into the blood in the lungs. Why don’t these processes proceed in the opposite direction? 2. Many students struggle with fundamental aspects of fetal circulation and respiration. Students might assume that the mother’s blood flows through the umbilical cord into the fetus. Students might also expect that the fetus is somehow breathing air. Nobody likes to be embarrassed by ignorance, so gauging these and many other misconceptions can be a challenge. To better understand your students’ background knowledge consider giving a short quiz on fundamental points before lecturing on the subject. Teaching Tips Figure is an especially helpful depiction of the movements of gases in the human respiratory system. The figure includes all of the main sites where oxygen is consumed, the alveoli where gas exchange occurs in the lungs, and the separate movement of oxygenated and deoxygenated blood through the heart. © 2012 Pearson Education, Inc. 53

Gases move from areas of higher concentration to areas of lower concentration. Gases in the alveoli of the lungs have more O2 and less CO2 than gases in the blood. O2 moves from the alveoli of the lungs into the blood. CO2 moves from the blood into the alveoli of the lungs. The tissues have more CO2 and less O2 than gases in the blood. CO2 moves from the tissues into the blood. O2 moves from the blood into the tissues. Student Misconceptions and Concerns 1. Many students still struggle with the concept of diffusion as the main mechanism of gas transport. Before discussing gas transport, ask your class to explain why oxygen moves out of the blood in body tissues, but into the blood in the lungs. Why don’t these processes proceed in the opposite direction? 2. Many students struggle with fundamental aspects of fetal circulation and respiration. Students might assume that the mother’s blood flows through the umbilical cord into the fetus. Students might also expect that the fetus is somehow breathing air. Nobody likes to be embarrassed by ignorance, so gauging these and many other misconceptions can be a challenge. To better understand your students’ background knowledge consider giving a short quiz on fundamental points before lecturing on the subject. Teaching Tips Figure is an especially helpful depiction of the movements of gases in the human respiratory system. The figure includes all of the main sites where oxygen is consumed, the alveoli where gas exchange occurs in the lungs, and the separate movement of oxygenated and deoxygenated blood through the heart. © 2012 Pearson Education, Inc. 54

Animation: CO2 from Blood to Lungs
Student Misconceptions and Concerns 1. Many students still struggle with the concept of diffusion as the main mechanism of gas transport. Before discussing gas transport, ask your class to explain why oxygen moves out of the blood in body tissues, but into the blood in the lungs. Why don’t these processes proceed in the opposite direction? 2. Many students struggle with fundamental aspects of fetal circulation and respiration. Students might assume that the mother’s blood flows through the umbilical cord into the fetus. Students might also expect that the fetus is somehow breathing air. Nobody likes to be embarrassed by ignorance, so gauging these and many other misconceptions can be a challenge. To better understand your students’ background knowledge consider giving a short quiz on fundamental points before lecturing on the subject. Teaching Tips Figure is an especially helpful depiction of the movements of gases in the human respiratory system. The figure includes all of the main sites where oxygen is consumed, the alveoli where gas exchange occurs in the lungs, and the separate movement of oxygenated and deoxygenated blood through the heart. Animation: CO2 from Blood to Lungs Right click on animation / Click play © 2012 Pearson Education, Inc. 55

Animation: CO2 from Tissues to Blood
Student Misconceptions and Concerns 1. Many students still struggle with the concept of diffusion as the main mechanism of gas transport. Before discussing gas transport, ask your class to explain why oxygen moves out of the blood in body tissues, but into the blood in the lungs. Why don’t these processes proceed in the opposite direction? 2. Many students struggle with fundamental aspects of fetal circulation and respiration. Students might assume that the mother’s blood flows through the umbilical cord into the fetus. Students might also expect that the fetus is somehow breathing air. Nobody likes to be embarrassed by ignorance, so gauging these and many other misconceptions can be a challenge. To better understand your students’ background knowledge consider giving a short quiz on fundamental points before lecturing on the subject. Teaching Tips Figure is an especially helpful depiction of the movements of gases in the human respiratory system. The figure includes all of the main sites where oxygen is consumed, the alveoli where gas exchange occurs in the lungs, and the separate movement of oxygenated and deoxygenated blood through the heart. Animation: CO2 from Tissues to Blood Right click on animation / Click play © 2012 Pearson Education, Inc. 56

Animation: O2 from Blood to Tissues
Student Misconceptions and Concerns 1. Many students still struggle with the concept of diffusion as the main mechanism of gas transport. Before discussing gas transport, ask your class to explain why oxygen moves out of the blood in body tissues, but into the blood in the lungs. Why don’t these processes proceed in the opposite direction? 2. Many students struggle with fundamental aspects of fetal circulation and respiration. Students might assume that the mother’s blood flows through the umbilical cord into the fetus. Students might also expect that the fetus is somehow breathing air. Nobody likes to be embarrassed by ignorance, so gauging these and many other misconceptions can be a challenge. To better understand your students’ background knowledge consider giving a short quiz on fundamental points before lecturing on the subject. Teaching Tips Figure is an especially helpful depiction of the movements of gases in the human respiratory system. The figure includes all of the main sites where oxygen is consumed, the alveoli where gas exchange occurs in the lungs, and the separate movement of oxygenated and deoxygenated blood through the heart. Animation: O2 from Blood to Tissues Right click on animation / Click play © 2012 Pearson Education, Inc. 57

Animation: O2 from Lungs to Blood
Student Misconceptions and Concerns 1. Many students still struggle with the concept of diffusion as the main mechanism of gas transport. Before discussing gas transport, ask your class to explain why oxygen moves out of the blood in body tissues, but into the blood in the lungs. Why don’t these processes proceed in the opposite direction? 2. Many students struggle with fundamental aspects of fetal circulation and respiration. Students might assume that the mother’s blood flows through the umbilical cord into the fetus. Students might also expect that the fetus is somehow breathing air. Nobody likes to be embarrassed by ignorance, so gauging these and many other misconceptions can be a challenge. To better understand your students’ background knowledge consider giving a short quiz on fundamental points before lecturing on the subject. Teaching Tips Figure is an especially helpful depiction of the movements of gases in the human respiratory system. The figure includes all of the main sites where oxygen is consumed, the alveoli where gas exchange occurs in the lungs, and the separate movement of oxygenated and deoxygenated blood through the heart. Animation: O2 from Lungs to Blood Right click on animation / Click play © 2012 Pearson Education, Inc. 58

Alveolar capillaries of lung Tissue cells throughout the body
Figure 22.10 CO2 in exhaled air O2 in inhaled air Alveolar epithelial cells Air spaces CO2 O2 CO2 O2 Alveolar capillaries of lung CO2-rich, O2-poor blood O2-rich, CO2-poor blood Figure Gas transport and exchange in the body Tissue capillaries Heart CO2 O2 CO2 Interstitial fluid O2 Tissue cells throughout the body 59

Alveolar capillaries of lung
Figure 22.10_1 O2 CO2 Alveolar capillaries of lung CO2-rich, O2-poor blood O2-rich, CO2-poor blood Figure 22.10_1 Gas transport and exchange in the body (detail) Tissue capillaries Heart CO2 O2 60

22.11 Hemoglobin carries O2, helps transport CO2, and buffers the blood
Most animals transport O2 bound to proteins called respiratory pigments. Blue, copper-containing pigment is used by molluscs and arthropods. Red, iron-containing hemoglobin is used by almost all vertebrates and many invertebrates and transports oxygen, buffers blood, and transports CO2. Student Misconceptions and Concerns 1. Many students still struggle with the concept of diffusion as the main mechanism of gas transport. Before discussing gas transport, ask your class to explain why oxygen moves out of the blood in body tissues, but into the blood in the lungs. Why don’t these processes proceed in the opposite direction? 2. Many students struggle with fundamental aspects of fetal circulation and respiration. Students might assume that the mother’s blood flows through the umbilical cord into the fetus. Students might also expect that the fetus is somehow breathing air. Nobody likes to be embarrassed by ignorance, so gauging these and many other misconceptions can be a challenge. To better understand your students’ background knowledge consider giving a short quiz on fundamental points before lecturing on the subject. Teaching Tips Students are often surprised to learn that the mineral iron in our diets is the same iron we use for building automobiles, pots, and pans. You might wish to point out that like the rust formed by the reaction of oxygen and iron, blood is also red, due to the bonding of oxygen to iron in our red blood cells. Furthermore, the familiar “metal” taste we experience when we have a cut in our mouth is due to the presence of iron in our blood. © 2012 Pearson Education, Inc. 61

O2 loaded in lungs O2 unloaded in tissues
Figure 22.11 Iron atom O2 loaded in lungs O2 O2 unloaded in tissues O2 Heme group Figure Hemoglobin loading and unloading O2 Polypeptide chain 62

Most CO2 in the blood enters red blood cells. Some CO2 combines with hemoglobin. Other CO2 reacts with water, forming carbonic acid, which then breaks apart into hydrogen ions and bicarbonate ions in a reversible reaction. Hemoglobin binds most of the H+ produced by this reaction, minimizing the change in blood pH. Student Misconceptions and Concerns 1. Many students still struggle with the concept of diffusion as the main mechanism of gas transport. Before discussing gas transport, ask your class to explain why oxygen moves out of the blood in body tissues, but into the blood in the lungs. Why don’t these processes proceed in the opposite direction? 2. Many students struggle with fundamental aspects of fetal circulation and respiration. Students might assume that the mother’s blood flows through the umbilical cord into the fetus. Students might also expect that the fetus is somehow breathing air. Nobody likes to be embarrassed by ignorance, so gauging these and many other misconceptions can be a challenge. To better understand your students’ background knowledge consider giving a short quiz on fundamental points before lecturing on the subject. Teaching Tips Students are often surprised to learn that the mineral iron in our diets is the same iron we use for building automobiles, pots, and pans. You might wish to point out that like the rust formed by the reaction of oxygen and iron, blood is also red, due to the bonding of oxygen to iron in our red blood cells. Furthermore, the familiar “metal” taste we experience when we have a cut in our mouth is due to the presence of iron in our blood. © 2012 Pearson Education, Inc. 63

Student Misconceptions and Concerns 1. Many students still struggle with the concept of diffusion as the main mechanism of gas transport. Before discussing gas transport, ask your class to explain why oxygen moves out of the blood in body tissues, but into the blood in the lungs. Why don’t these processes proceed in the opposite direction? 2. Many students struggle with fundamental aspects of fetal circulation and respiration. Students might assume that the mother’s blood flows through the umbilical cord into the fetus. Students might also expect that the fetus is somehow breathing air. Nobody likes to be embarrassed by ignorance, so gauging these and many other misconceptions can be a challenge. To better understand your students’ background knowledge consider giving a short quiz on fundamental points before lecturing on the subject. Teaching Tips Students are often surprised to learn that the mineral iron in our diets is the same iron we use for building automobiles, pots, and pans. You might wish to point out that like the rust formed by the reaction of oxygen and iron, blood is also red, due to the bonding of oxygen to iron in our red blood cells. Furthermore, the familiar “metal” taste we experience when we have a cut in our mouth is due to the presence of iron in our blood. © 2012 Pearson Education, Inc. 64

22.12 CONNECTION: The human fetus exchanges gases with the mother’s blood
A human fetus does not breathe with its lungs. Instead, it exchanges gases with maternal blood in the placenta. In the placenta, capillaries of maternal blood and fetal blood run next to each other. The fetus and mother do not share the same blood. Student Misconceptions and Concerns 1. Many students still struggle with the concept of diffusion as the main mechanism of gas transport. Before discussing gas transport, ask your class to explain why oxygen moves out of the blood in body tissues, but into the blood in the lungs. Why don’t these processes proceed in the opposite direction? 2. Many students struggle with fundamental aspects of fetal circulation and respiration. Students might assume that the mother’s blood flows through the umbilical cord into the fetus. Students might also expect that the fetus is somehow breathing air. Nobody likes to be embarrassed by ignorance, so gauging these and many other misconceptions can be a challenge. To better understand your students’ background knowledge consider giving a short quiz on fundamental points before lecturing on the subject. Teaching Tips Consider challenging your class to explain why a mother’s hemoglobin will release oxygen to the fetus. As noted in Module 22.12, fetal hemoglobin has a stronger affinity for oxygen. This is like a child pulling a toy away from an adult. © 2012 Pearson Education, Inc. 65

22.12 CONNECTION: The human fetus exchanges gases with the mother’s blood
Fetal hemoglobin attracts O2 more strongly than adult hemoglobin and takes oxygen from maternal blood. At birth CO2 in fetal blood increases and breathing control centers initiate breathing. Smoking during pregnancy reduces the supply of oxygen to the fetus by up to 25%. Student Misconceptions and Concerns 1. Many students still struggle with the concept of diffusion as the main mechanism of gas transport. Before discussing gas transport, ask your class to explain why oxygen moves out of the blood in body tissues, but into the blood in the lungs. Why don’t these processes proceed in the opposite direction? 2. Many students struggle with fundamental aspects of fetal circulation and respiration. Students might assume that the mother’s blood flows through the umbilical cord into the fetus. Students might also expect that the fetus is somehow breathing air. Nobody likes to be embarrassed by ignorance, so gauging these and many other misconceptions can be a challenge. To better understand your students’ background knowledge consider giving a short quiz on fundamental points before lecturing on the subject. Teaching Tips Consider challenging your class to explain why a mother’s hemoglobin will release oxygen to the fetus. As noted in Module 22.12, fetal hemoglobin has a stronger affinity for oxygen. This is like a child pulling a toy away from an adult. © 2012 Pearson Education, Inc. 66

Figure 22.12 Placenta, containing maternal blood vessels and fetal capillaries Umbilical cord, containing fetal blood vessels Amniotic fluid Figure A human fetus and placenta in the uterus Uterus 67

You should now be able to
Describe the three main phases of gas exchange in a human. Describe four types of respiratory surfaces and the kinds of animals that use them. Explain how the amount of oxygen available in air compares to that available in cold and warm fresh water and cold and warm salt water. Explain how the structure and movements of fish gills maximize oxygen exchange. © 2012 Pearson Education, Inc. 68

Explain why breathing air is easier than using water for gas exchange. Describe the tracheal system of insects. Describe the respiratory structures of the fossil animal Tiktaalik. Explain how the metabolic rate of a vertebrate corresponds to the nature of its respiratory system. Describe the structures and corresponding functions of a mammalian respiratory system. © 2012 Pearson Education, Inc. 69

Describe the impact of smoking on human health. Compare the mechanisms and efficiencies of lung ventilation in humans and birds. Explain how breathing is controlled in humans. Explain how blood transports gases between the lungs and tissues of the body. Describe the functions of hemoglobin. Explain how a human fetus obtains oxygen prior to and immediately after birth. © 2012 Pearson Education, Inc. 70

Water flow between lamellae
Figure 22.UN01 Lamella Water flow between lamellae Figure 22.UN01 Reviewing the Concepts, 22.3 Blood flow 71

requires moist, thin often relies on binds and transports
Figure 22.UN02 Gas exchange requires moist, thin often relies on (a) (b) for exchange of to transport gases between red blood cells contain O2 CO2 (c) (d) needed for waste product of mammals ventilate by binds and transports and (e) Figure 22.UN02 Connecting the Concepts, question 1 helps to (f) tissue cells (g) regulated by breathing control center transport CO2 and buffer the blood 72

Figure 22.UN03 a. b. c. d. e. f. Figure 22.UN03 Connecting the Concepts, question 2 g. h. 73

O2 saturation of hemoglobin (%)
Figure 22.UN04 100 Llama 80 Human 60 O2 saturation of hemoglobin (%) 40 Figure 22.UN04 Applying the Concepts, question 13 20 P (mm Hg) O2 74

Chapter 22 Gas Exchange.

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