Circulatory, Respiratory, and Excretory Systems

• • • • •• ••••••••

34

Reading Essentials Chapter 34 Circulatory, Respiratory, and Excretory Systems 405

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.

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.

• • •• •••••••••• • • • • • •

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.

• • •• •••• ••••••••••••••••

• • • ••• ••••••••

•• ••• •••••••

•••• •• •• • • • • • •

• •• • •• • •••••••••

• •• • • •• • • • • • • • • • • •

•• • • ••••••

• • •• •• ••••••••••••••

• •••• •••••••••• • • •••• •••••••••••••••

• • •• • • • •••••••••••

•••• • • • •

• • •• • • • •••••••••••

• ••••••••••• • •••• •• •••••••••

• •• •

• • • •• •

• •• • • •

• •• • • • • • • •

••••••••••

• • • •••• •••••••••••• •• • •• •• ••••••••••••

• •• • •• •• ••••••••••••

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.

• •• • • •• • • • • • • • • • • •

• •• •••••

•• • • •• ••• • • • • • • • • • • • • • • • •• ••• • • • • • • • • • • •

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.