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BIO 103 CHAPTER 22
Gas Exchange
Learning Targets
Mechanisms of Gas Exchange
22.1
22.2
22.3
22.3
22.4
22.4
22.5
22.5
Describe the three main phases of gas exchange in a human.
Describe the properties of respiratory surfaces. 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.
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, and explain why these features
have led scientists to conclude that it likely lived in shallow water.
Explain how the metabolic rate of a vertebrate corresponds to the nature of its respiratory system.
The Human Respiratory System
22.6
22.7
22.8
22.9
Describe the structures and corresponding functions of a mammalian respiratory system. Describe
the causes and symptoms of respiratory distress
syndrome and COPD.
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.
Transport of Gases in the Human Body
22.10 Explain how blood transports gases between the lungs and tissues of the body.
22.11 Describe the functions of hemoglobin. Explain how carbon dioxide is transported in the blood.
22.12 Explain how a human fetus obtains oxygen prior to and immediately after birth.
Key Terms
alveoli (s. alveolus)
breathing control center
bronchi (s. bronchus)
bronchioles
countercurrent exchange
diaphragm
gas exchange
gills
hemoglobin
larynx
lungs
negative pressure breathing
partial pressure
pharynx
surfactant
trachea
tracheal system
ventilation
vital capacity
vocal cords
Lecture Outline
I. Introduction
A. People cannot survive for long in the air at the world’s highest peaks in the Himalayan Mountains.
B. Yet twice a year, flocks of geese migrate over the Himalayas.
C. How can geese fly where people cannot breathe?
1. Geese have more efficient lungs than humans, and
2. their hemoglobin has a very high affinity for oxygen.
II. Mechanisms of Gas Exchange
A. 22.1 Overview: Gas exchange in humans involves breathing, transport of gases, and
exchange with body cells
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B.
C.
D.
E.
1. The process of gas exchange is sometimes called respiration, the interchange of
a. O2 and the waste product CO2
b. between an organism and its environment.
2. Three phases of gas exchange occur in humans and other animals with lungs:
a. breathing,
b. transport of oxygen and carbon dioxide in blood, and
c. exchange of gases with body cells.
i. Body tissues take up oxygen and
ii. release carbon dioxide.
3. Cellular respiration requires a continuous supply of oxygen and the disposal of carbon dioxide.
22.2 Animals exchange O2 and CO2 across moist body surfaces
1. Respiratory surfaces must be
a. moist for diffusion of O2 and CO2 and
b. thin, to best facilitate diffusion.
2. The skin may be used for gas exchange in animals that are
a. wet and
b. small.
c. Earthworms are an example.
3. Most animals have specialized body parts that promote gas exchange:
a. gills in fish and amphibians,
b. tracheal systems in arthropods, and
c. lungs in tetrapods that live on land, such as
i. amphibians,
ii. reptiles, including birds, and
iii. mammals.
22.3 Gills are adapted for gas exchange in aquatic environments
1. Gills
a. are extensions of the body,
b. increase the surface to volume ratio, and
c. increase the surface area for gas exchange.
i. Oxygen is absorbed.
ii. Carbon dioxide is released.
2. In a fish, gas exchange is enhanced by
a. ventilation of the gills (moving water past the gills) and
b. countercurrent flow of water and blood.
3. Gas exchange with water has its limits.
a. Water holds only about 3% of the oxygen in air.
b. Cold water holds more oxygen than warm water.
c. Fresh water holds more oxygen than salt water.
d. Turbulent water holds more oxygen than still water.
22.4 The tracheal system of insects provides direct exchange between the air and body cells
1. Compared to water, using air to breathe has two big advantages.
a. Air contains higher concentrations of O2 than water.
b. Air is lighter and easier to move than water.
2. However, air-breathing animals lose water through their respiratory surfaces.
3. Insect tracheal systems use tiny branching tubes that
a. reduce water loss and
b. pipe air directly to cells.
22.5 EVOLUTION CONNECTION: The evolution of lungs facilitated the movement of tetrapods onto
land
1. Tetrapods seem to have evolved in shallow water.
a. Fossil fish with legs had lungs and gills.
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b. Legs may have helped them lift up to gulp air.
c. The fossil fish Tiktaalik
i. lived about 375 million years ago and
ii. illustrates these air-breathing adaptations.
2. The first tetrapods on land diverged into three major lineages.
a. Amphibians use small lungs and their body surfaces.
b. Nonbird reptiles have
i. lower metabolic rates and
ii. simpler lungs.
c. Birds and mammals have
i. higher metabolic rates and
ii. more complex lungs.
III. The Human Respiratory System
A. 22.6 In mammals, branching tubes convey air to lungs located in the chest cavity
1. The diaphragm
a. separates the abdominal cavity from the thoracic cavity and
b. helps ventilate the lungs.
2. In mammals, air is inhaled through the nostrils into the nasal cavity. Air is
a. filtered by hairs and mucus surfaces,
b. warmed and humidified, and
c. sampled for odors.
3. From the nasal cavity, air next passes
a. to the pharynx,
b. then larynx, past the vocal cords,
c. into the trachea, held open by cartilage rings,
d. into the paired bronchi,
e. into bronchioles, and finally
f. to the alveoli, grapelike clusters of air sacs, where gas exchange occurs.
4. Alveoli are well adapted for gas exchange with high surface areas of capillaries
5. In alveoli,
a. O2 diffuses into the blood and
b. CO2 diffuses out of the blood.
6. Surfactants are specialized secretions required to keep the walls of the small alveoli from sticking
shut.
a. Babies born 6 weeks or more before their due date often struggle with respiratory distress syndrome due to an inadequate amount of lung surfactant.
b. Artificial surfactants are now administered to preterm infants.
7. Exposure to pollutants can cause continual irritation and inflammation of the lungs.
a. Examples of common lung pollutants include
i. air pollution and
ii. tobacco smoke.
b. Chronic obstructive pulmonary disease (COPD) can result limiting
i. lung ventilation and
ii. gas exchange.
B. 22.7 CONNECTION: Smoking is a serious assault on the respiratory system
1. Mucus and cilia in the respiratory passages
a. sweep contaminant-laden mucus up and out of the airways and
b. can be damaged by smoking.
2. One of the worst sources of lung-damaging air pollutants is tobacco smoke, containing more than
4,000 chemicals.
3. Without healthy cilia, smokers must cough to clear dirty mucus from the trachea.
4. Smoking can cause
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a. lung cancer,
b. cardiovascular disease, and
c. emphysema.
5. Smoking accounts for 90% of all lung cancer cases.
6. Smoking increases the risk of other types of cancer.
7. Smoking also
a. increases the risk of heart attacks and strokes,
b. raises blood pressure, and
c. increases harmful types of cholesterol.
8. Every year in the United States, smoking
a. kills about 440,000 people,
b. more than all the deaths from accidents, alcohol, drug abuse, HIV, and murders
combined.
9. Adults who smoke die 13–14 years earlier than nonsmokers.
C. 22.8 Negative pressure breathing ventilates your lungs
1. Breathing is the alternate inhalation and exhalation of air (ventilation).
2. In mammals, inhalation occurs when
a. the rib cage expands,
b. the diaphragm moves downward,
c. the pressure around the lungs decreases, and
d. air is drawn into the respiratory tract.
3. This type of ventilation is called negative pressure breathing.
4. Exhalation occurs when
a. the rib cage contracts,
b. the diaphragm moves upward,
c. the pressure around the lungs increases, and
d. air is forced out of the respiratory tract.
5. Not all air is expelled during exhalation.
a. Some air still remains in the trachea, bronchi, bronchioles, and alveoli.
b. This remaining air is “dead air.”
c. Thus, inhalation mixes fresh air with dead air.
6. One-way flow of air in birds
a. reduces dead air and
b. increases their ability to obtain oxygen.
D. 22.9 Breathing is automatically controlled
1. Breathing is usually under automatic control.
2. Breathing control centers in the brain sense and respond to CO2 levels in the blood.
3. A drop in blood pH increases the rate and depth of breathing.
IV. Transport of Gases in the Human Body
A. 22.10 Blood transports respiratory gases
1. The heart pumps blood to two regions.
a. The right side pumps oxygen-poor blood to the lungs.
b. The left side pumps oxygen-rich blood to the body.
2. In the lungs, blood picks up O2 and drops off CO2.
3. In the body tissues, blood drops off O2 and picks up CO2.
4. A mixture of gases, such as air, exerts pressure.
a. Each kind of gas in a mixture accounts for a portion of the total pressure of the
mixture.
b. Thus, each gas has a partial pressure.
c. The exchange of gases between capillaries and the surrounding cells is based on
partial pressures.
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d. Molecules of each kind of gas diffuse down a gradient of its own partial pressure, moving from
regions of
i. higher partial pressure to
ii. lower partial pressure.
5. Gases move from areas of higher concentration to areas of lower concentration.
a. Gases in the alveoli of the lungs have more O2 and less CO2 than gases in the blood.
i. O2 moves from the alveoli of the lungs into the blood.
ii. CO2 moves from the blood into the alveoli of the lungs.
b. The tissues have more CO2 and less O2 than gases in the blood.
i. CO2 moves from the tissues into the blood.
ii. O2 moves from the blood into the tissues.
B. 22.11 Hemoglobin carries O2, helps transport CO2, and buffers the blood
1. Most animals transport O2 bound to proteins called respiratory pigments.
a. Blue, copper-containing pigment is used by
i. molluscs and
ii. arthropods.
b. Red, iron-containing hemoglobin
i. is used by almost all vertebrates and many invertebrates and
ii. transports oxygen, buffers blood, and transports CO2.
2. Most CO2 in the blood enters red blood cells.
3. Some CO2 combines with hemoglobin.
4. Other CO2 reacts with water, forming carbonic acid, which then breaks apart into
a. hydrogen ions and
b. bicarbonate ions in a reversible reaction.
c. Hemoglobin binds most of the H+ produced by this reaction, minimizing the change in blood pH.
C. 22.12 CONNECTION: The human fetus exchanges gases with the mother’s blood
1. A human fetus does not breathe with its lungs. Instead, it exchanges gases with maternal blood in
the placenta.
2. 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.
3. Fetal hemoglobin
a. attracts O2 more strongly than adult hemoglobin and
b. takes oxygen from maternal blood.
4. At birth
a. CO2 in fetal blood increases and
b. breathing control centers initiate breathing.
5. Smoking during pregnancy reduces the supply of oxygen to the fetus by up to 25%.
Word Roots
alveol- = a cavity (alveolus [plural, alveoli]: one of the millions of tiny dead-end sacs within vertebrate lungs
where gas exchange occurs)
bronch- = branch (bronchiole: a thin breathing tube that branches from a bronchus within a lung; bronchus
[plural, bronchi]: one of a pair of breathing tubes that branch from the trachea into the lungs)
counter- = opposite (countercurrent exchange: the transfer of a substance or heat between two fluids flowing in opposite directions)
hemo- = blood (hemoglobin: an iron-containing protein in red blood cells that reversibly binds O2 and transports it to body tissues)
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