Download organs Working together Did You Know?

3.5
Breathing is something you do all day, every day—mostly
without even thinking about it. In this section, you will find
out more about the organ system that is most involved in
breathing: the respiratory system.
Organs Working Together
The respiratory system is one of the major organ systems of
the body. It is made up of the lungs, bronchi, trachea, and other
structures. Figure 1 shows air that enters through the mouth and
nose and passes through the throat. From there, it travels through
the trachea (windpipe), which divides into two branches called
bronchi (singular: bronchus).
The cells lining the trachea and bronchi are covered in cilia. The
cilia are imbedded in a layer of mucus, which traps bacteria and
particles of dirt from the air (Figure 2). The cilia move together
to sweep the mucus upwards, away from the delicate tissues in
the lungs.
dig deeper
Did You Know?
A Lot of Hot Air
At rest, the average person
moves more than 10 000 L
of air in and out of the lungs
each day!
▶▶ respiratory system:
the organ system that
is made up of the nose,
mouth, trachea, bronchi,
and lungs; the organ
system responsible for
taking in oxygen and
removing carbon dioxide
from the body
▶▶ trachea: tube leading from
the throat to the bronchi
▶▶ bronchi: (singular:
bronchus) tubes that
carry air into the lungs
nasal cavity
mouth
cells covered
in cilia
trachea
bronchus
lung
Figure 2 Cilia help
move mucus and foreign
materials out of airways.
Figure 1 The human respiratory system
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3.5 The Respiratory System 79
Gas Exchange
alveoli
capillary
network
Figure 3 Each air sac is
surrounded by a capillary
network to ensure a good
blood supply.
carbon
dioxide
oxygen
Air is a mixture of gases. Oxygen makes up about 21 % of air by
volume. The lungs absorb oxygen from this mixture. How does this
occur? Like a tree trunk that divides into smaller branches, bronchi
branch again and again, ending in tiny air sacs (Figure 3). Each
sac is surrounded by a network of capillaries. Capillaries are tiny,
thin-walled blood vessels that are part of the circulatory system.
(You will learn about the circulatory system later in this chapter.)
Both the air sacs and the capillaries are made up of a layer of
epithelial tissue that is only one cell thick.
Oxygen Transport
Oxygen moves into the capillaries by diffusion. As you know, diffusion
is the movement of a substance from an area where it is more
concentrated to an area where it is less concentrated. The air we
breathe into our lungs has a higher concentration of oxygen than the
blood in the capillaries around the air sacs. Therefore, the oxygen
diffuses through the air sac and the capillary into the blood (Figure 4).
Removing Carbon Dioxide
capillary
red blood cells
Figure 4 The air sac
provides a huge surface
area in the lungs across
which oxygen and carbon
dioxide can diffuse.
Oxygen moves from the lungs into the blood, and the blood
transports the oxygen to other parts of the body. Here, oxygen
diffuses out of the blood and into the body tissues. At the same
time, carbon dioxide diffuses from the tissues into the blood.
Carbon dioxide is a waste gas produced by the body as the body
uses energy to move, grow, and repair itself. The blood carries
carbon dioxide to the lungs. The carbon dioxide diffuses from the
blood into the air sac. The carbon dioxide is then released through
the mouth or nose when we breathe out. The taking in of oxygen
and the releasing of carbon dioxide is called gas exchange: our
bodies exchange carbon dioxide for oxygen.
Breathing
▶▶ diaphragm: a large sheet
of muscle underneath the
lungs
The process of breathing involves alternately drawing air into the
lungs (inhalation) and then pushing air out (exhalation). Breathing
uses muscles that move the ribs and the diaphragm, a large sheet
of muscle underneath the lungs. When the muscles and diaphragm
relax, they move inward and air is pushed out of the lungs. When
the muscles and diaphragm contract, they move outward and air is
pulled into the lungs (Figure 5 on the next page).
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exhalation
lung volume decreases
rib
cage
muscles relax,
diaphragm is dome-shaped
inhalation
lung volume increases
trachea
lungs
muscles contract,
diaphragm flattens
Figure 5 Exhalation pushes air out of the lungs; inhalation draws air
into the lungs.
Control of Breathing
Some breathing is voluntary. Singers control their
breathing in order to hold notes. Swimmers use
controlled breathing as they move their faces
in and out of water (Figure 6). Mostly, though,
breathing is involuntary. We do not have to think
about this life function; our bodies simply do it.
Though we can choose to breathe in or hold our
breath for a period of time, sensors in the brain
cause the body to resume involuntary breathing
action after just a short time. Give it a try! How
long can you hold your breath?
The brain controls breathing. When you hold
your breath, carbon dioxide builds up in your
Figure 6 A swimmer must carefully control their
blood. Sensors in your circulatory system detect
breathing to avoid inhaling water.
the increase of carbon dioxide. They send a
signal to the brain. In response, the brain sends
messages to the diaphragm and to the muscles of the rib cage to
contract. The diaphragm flattens when it contracts. At the same
time, muscles contract to raise the rib cage. These movements
expand the lungs and draw oxygen-rich air into them. Carbon
dioxide can now leave the blood, and more oxygen can enter it.
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3.5 The Respiratory System 81
Respiratory Diseases
Diseases that reduce the flow of air into and out of the lungs are
called chronic obstructive pulmonary diseases (COPD). These
diseases make it difficult to breathe, are often permanent, and may
get worse over time. The symptoms of these diseases are often
made worse by air pollution. This is why the media advise people
with respiratory problems to stay indoors on “bad-air days.”
Figure 7 The destruction
of the air sacs reduces
the surface area through
which oxygen can move
into the blood.
There are three main types of COPD: asthma, emphysema, and
chronic bronchitis. Asthma is a respiratory disease that involves
airway swelling and mucus production. People with asthma usually
have periods of wellness between episodes.
Emphysema is another respiratory disease. With emphysema, the
tiny air sacs in the lungs collapse and the walls between them are
destroyed. The surface area through which oxygen diffuses is smaller
and less oxygen can be picked up by the blood (Figure 7).
Chronic bronchitis is a respiratory disease in which tissues
lining the airway become swollen. The passageway for air is
narrowed (Figure 8), causing coughing and breathlessness. As with
emphysema, less oxygen reaches body cells. Both emphysema and
chronic bronchitis generally worsen over time.
Figure 8 In bronchitis, airways are narrowed by swelling and mucus production.
Causes of Respiratory Disease
Figure 9 Wearing a
respirator mask protects
your airways from
particles and fumes.
Your body needs to breathe clean air. Smokers and those exposed
to second-hand smoke are at greater risk of developing asthma,
chronic bronchitis, and emphysema. Exposure to pollution is
another risk factor for respiratory disease. Recent studies show that
exposure to chlorine in swimming pools can increase your chance
of getting asthma. You can protect the health of your respiratory
system by not smoking and avoiding being around others who
smoke. Wear a respirator mask if you think you will be exposed to
harmful materials in the air (Figure 9).
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CITIZENACTION
Air Pollution
Have you ever seen a car parked outside a store with
its engine still on while the driver goes inside to get
something? What about cars that are running while
the driver waits to pick someone up? Cars release
a lot of harmful fumes into the air (Figure 10). Some
cities are introducing “no-idling” bylaws to help
reduce the amount of fumes released by cars. The
idea is to reduce climate change and to improve air
quality.
Analyze your observations and summarize them in
a letter to your mayor and city council. Explain what
you would like done to enforce no-idling bylaws near
your school.
What Can You Do to Help?
Find out whether there are “no-idle” zones near your
school. Do all drivers turn off their engines when they
stop there? Conduct a survey: over several days,
observe and record how many and what kinds of
vehicles you see idling outside your school. How long
do they leave their engines running?
Figure 10 Air pollution can cause respiratory problems
such as bronchitis and asthma.
Unit Task
3.5 Wrap Up
• The task of the respiratory system is to exchange oxygen and carbon
dioxide between the body and its surroundings.
• The main parts of the respiratory system are the nose, mouth, trachea,
bronchi, lungs, rib cage and muscles, and diaphragm.
• Gas exchange takes place in the air sacs in the lungs. These sacs are
surrounded by capillaries.
Bookmark
You can apply what you
learned in this activity
about the effects of air
quality to the Unit Task
described on page 146.
• The circulatory system delivers oxygen to, and removes carbon dioxide
from, all of the body’s tissues.
• Chronic obstructive pulmonary diseases (COPD) affect the ability of the
respiratory system to exchange gases.
• Environmental pollutants can cause COPD, and can worsen the symptoms
of these diseases.
Check Your Learning
1.Describe the path oxygen takes when it enters the
respiratory system. K /U
2.What is the role of cilia in the respiratory
system? K/U
3.How does breathing result in gas exchange? K/U
4.Compare and contrast three types of respiratory
disease. K/U
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5.Curare is a drug used by South American native
hunters. It paralyzes the muscles of the animals
they hunt. How does this affect the animals’ ability
to breathe? A
6.Spaceships and submarines have technology
on board to remove carbon dioxide from the air.
Explain why this technology is necessary. C A
3.5 The Respiratory System 83