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Circulatory, Respiratory, and Excretory Systems
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Reading Essentials Chapter 34 Circulatory, Respiratory, and Excretory Systems 405
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section l Respiratory System2
Before You Read
Breathing happens automatically. You do not think about
every breath you take. Look at the clock and count how many
breaths you take in a minute. Write that number on the lines
below. Then write one sentence describing a time when you
did think about your breathing. In this section you will learn
what happens in your body as you breathe.
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The respiratory system
exchanges oxygen and
carbon dioxide between the
atmosphere and the blood
and between the blood and
the body’s cells.
What You’ll Learnn the difference between internal
and external respirationn the path of air through the
respiratory systemn the changes that occur in the
body during breathing
The Importance of RespirationYour body’s cells need oxygen. Recall that cells use oxygen
and glucose to produce energy-rich ATP molecules needed for
cellular metabolism. This process is called cellular respiration.
Cellular respiration releases energy. It also releases carbon
dioxide and water.
How is breathing different from respiration?The respiratory system supports cellular respiration by
supplying oxygen to body cells and removing carbon dioxide
waste from cells. Two processes make up the respiratory
system: breathing and respiration.
First, air enters the body. Breathing is the mechanical
movement of air into and out of the lungs. Second, gases
are exchanged. External respiration is the exchange of gases
between the atmosphere and the blood. Internal respiration is
the exchange of gases between the blood and the body’s cells.
Read to LearnMain Ideas As you read the
section, highlight the main ideas
in each paragraph.
1. Explain why one form
of respiration is called
“external.”
Biology/Life Sciences 9.a Students know how the complementary activity of major body systems provides cells with oxygen
and nutrients and removes toxic waste products such as carbon dioxide. Also covers: I&E 1.d
406 Chapter 34 Circulatory, Respiratory, and Excretory Systems Reading Essentials
Copyr
ight
© G
lencoe/M
cG
raw
-Hill, a
div
isio
n o
f The M
cG
raw
-Hill C
om
panie
s, In
c.
The Path of AirAs you read about the path air travels through your body,
follow along in the fi gure below. First, air enters your mouth
or nose. Hairs in your nose fi lter out dust in the air. Hairlike
cilia that line your nasal passages trap particles from the air
and sweep them toward the throat. This keeps particles from
entering the lungs. Mucous membranes beneath the cilia warm
and moisten the air, while trapping foreign particles.
What structures does air pass through as it
travels to the lungs?Filtered air then passes through the upper throat, or pharynx
(FER ingks). A fl ap called the epiglottis covers the opening
to the larynx (LER ingks). The epiglottis allows air to pass
while keeping food out of the respiratory tubes. Air moves
through the larynx to a tube in the chest called the trachea
(TRAY kee uh), or windpipe. The trachea branches into two
large tubes, called bronchi (BRAHN ki). The bronchi lead
to the lungs, where gas exchange takes place. Each bronchus
branches into smaller bronchioles (BRAHN kee ohlz).
Branching continues until each branch ends in an air sac called
an alveolus (al VEE uh lus) (plural, alveoli). Alveoli have walls
that are one cell thick and are surrounded by capillaries.
How does gas exchange occur?Oxygen in the air diffuses across the thin walls of the
alveoli into capillaries and then into red blood cells. The
blood carries the oxygen to the cells. At the same time, carbon
dioxide moves from the blood into the capillaries. It diffuses
into the alveoli to be returned to the atmosphere.
Picture This 3. Identify Circle the name
of the structure in which
oxygen diffuses.
2. Identify three fi lters
through which air passes on
its way through your nose
and nasal passages.
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Chapter 34 Circulatory, Respiratory, and Excretory Systems 407
Copyr
ight
© G
lencoe/M
cG
raw
-Hill, a
div
isio
n o
f The M
cG
raw
-Hill C
om
panie
s, In
c.
biologygmh.com
BreathingYour brain directs the rate of your breathing. If you have a
lot of carbon dioxide in your blood, you need more oxygen, so
you breathe faster.
As shown in the fi gure below, the rib and diaphragm
muscles contract during inhalation. This increases the size of
the chest cavity, allowing air to move into the lungs. During
exhalation, the rib and diaphragm muscles relax. This reduces
the size of the chest cavity, allowing air to fl ow out.
Picture This 4. Compare how the
diaphragm moves during
inhalation and exhalation.
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Picture This 5. Identify the lung disorder
that damages the alveoli.
Lung Disorder Description
Asthma Respiratory pathways become irritated and bronchioles constrict.
Bronchitis Infected respiratory pathways result in coughing and production of mucus.
Emphysema Alveoli break down, resulting in reduced surface area needed for gas exchange.
Pneumonia Infection in the lungs causes alveoli to collect mucus.
Pulmonary tuberculosis
A bacterium infects the lungs, harming the capillaries surrounding the alveoli and inhibiting gas exchange.
Lung cancer Uncontrolled cell growth in the lungs can lead to persistent cough, shortness of breath, bronchitis or pneumonia, and death.
Respiratory DisordersThe table below lists common disorders that affect the
respiratory system. Smoking irritates respiratory tissues and
inhibits cellular metabolism. Allergic reactions to particles in
the air can also lead to respiratory problems.