The Respiratory System

Say Thanks to the AuthorsClick http://www.ck12.org/saythanks

(No sign in required)

To access a customizable version of this book, as well as otherinteractive content, visit www.ck12.org

CK-12 Foundation is a non-profit organization with a mission toreduce the cost of textbook materials for the K-12 market bothin the U.S. and worldwide. Using an open-content, web-basedcollaborative model termed the FlexBook®, CK-12 intends topioneer the generation and distribution of high-quality educationalcontent that will serve both as core text as well as provide anadaptive environment for learning, powered through the FlexBookPlatform®.

Copyright © 2014 CK-12 Foundation, www.ck12.org

The names “CK-12” and “CK12” and associated logos and theterms “FlexBook®” and “FlexBook Platform®” (collectively“CK-12 Marks”) are trademarks and service marks of CK-12Foundation and are protected by federal, state, and internationallaws.

Any form of reproduction of this book in any format or medium,in whole or in sections must include the referral attribution linkhttp://www.ck12.org/saythanks (placed in a visible location) inaddition to the following terms.

Except as otherwise noted, all CK-12 Content (including CK-12Curriculum Material) is made available to Users in accordancewith the Creative Commons Attribution-Non-Commercial 3.0Unported (CC BY-NC 3.0) License (http://creativecommons.org/licenses/by-nc/3.0/), as amended and updated by Creative Com-mons from time to time (the “CC License”), which is incorporatedherein by this reference.

Complete terms can be found at http://www.ck12.org/terms.

Printed: February 9, 2014

www.ck12.org Concept 1. The Respiratory System

CONCEPT 1 The Respiratory System

Lesson Objectives

• Identify the parts of the respiratory system.• Identify the main function of the respiratory system.• Describe how breathing works.• Outline how the respiratory system and the cardiovascular system work together.• Identify how breathing and cellular respiration are connected.

Check Your Understanding

• What is an organ system?• What is the role of the circulatory system?• How does your blood get oxygen?

Vocabulary

• alveoli• diaphragm• epiglottis• exhalation• external respiration• gas exchange• inhalation• internal respiration• larynx• pharynx• respiration• respiratory system• trachea

Roles of the Respiratory System

You breathe mostly without thinking about it. Remember how uncomfortable you felt the last time you had a coldor a cough? You usually do not think about your respiratory system or how it works until there is a problem with it.Every cell in your body depends on your respiratory system.

Your respiratory system is made up of the tissues and organs that allow oxygen to enter the body and carbon dioxideto leave your body. Organs in your respiratory system include your:

• Nose.• Mouth.• Larynx.• Pharynx.• Lungs.• Diaphragm.

1

www.ck12.org

These structures are shown in Figure 1.1.

FIGURE 1.1The respiratory system. Air moves inthrough the nose and mouth and downthe trachea, which is a long, straight tubein the chest.

Parts of the Respiratory System

Figure 1.1 shows many of the structures of the respiratory system. Each of the parts has a specific job. The parts ofthe respiratory system include the following:

• The diaphragm is a sheet of muscle that spreads across the bottom of the rib cage. When the diaphragmcontracts, the chest volume gets larger and the lungs take in air. When the diaphragm relaxes, the chestvolume gets smaller and air is pushed out of the lungs.

• The nose and nasal cavity filter, warm, and moisten the air you breathe. The nose hairs and mucus producedby the cells in the nose catch particles in the air and keep them from entering the lungs. When particles in theair do reach the lungs, what do you think happens?

• Behind the nasal cavity, air passes through the pharynx, a long tube. Both food and air pass through thepharynx.

• The larynx, also called the "voice box," is found just below the pharynx. Your voice comes from your larynx.Air from the lungs passes across thin tissues in the larynx and produces sound.

• The trachea, or windpipe, is a long tube that leads down to the lungs, where it divides into the right and leftbronchi. The bronchi branch out into smaller bronchioles in each lung.

• Since food goes down the pharynx, how is it stopped from entering the trachea? A flap of tissue called theepiglottis closes over the trachea when food is swallowed to prevent choking or inhaling food.

• The bronchioles lead to the alveoli. Alveoli are the little sacs at the end of the bronchioles. They look likelittle bunches of grapes, as shown in Figure 1.2. Oxygen is exchanged for carbon dioxide in the alveoli. Gas

2

www.ck12.org Concept 1. The Respiratory System

exchange is the name we give to the process that allows oxygen to enter the blood and carbon dioxide to moveout of the blood - the two gases are "exchanged."

FIGURE 1.2The alveoli are the tiny grape-like struc-tures in the lungs and the sites of gasexchange.

How We Breathe

Most of the time, you breathe without thinking about it. Breathing is mostly an involuntary action that is controlledby a part of your brain that also controls your heart beat. If you swim, do yoga, or sing, you know you can alsocontrol your breathing. Taking air into the body through the nose and mouth is called inhalation. Pushing air out ofthe body through the nose or mouth is called exhalation. The man in Figure 1.3 is exhaling before he surfaces fromthe pool water.

How do lungs allow air in? As mentioned above, air moves into and out of the lungs by the movement of muscles.The diaphragm and rib muscles contract and relax to move air into and out of the lungs. During inhalation, thediaphragm contracts and moves downward. The rib muscles contract and cause the ribs to move outward. Thiscauses the chest volume to increase. Because the chest volume is larger, the air pressure inside the lungs is lowerthan the air pressure outside. This difference in air pressures causes air to be sucked into the lungs. When thediaphragm and rib muscles relax, air is pushed out of the lungs. Exhalation is similar to letting the air out of aballoon.

The walls of the alveoli are very thin and allow gases to enter into them. The alveoli are lined with capillaries. Thesecapillaries are shown in Figure 1.4. Oxygen moves from the alveoli to the blood in the capillaries that surround thealveoli. At the same time, carbon dioxide moves in the opposite direction, from capillary blood to the alveoli.

Breathing and Respiration

When you breath in, oxygen is drawn in through the mouth and down into the lungs. The oxygen then passes acrossthe thin lining of the capillaries and into the blood. The oxygen molecules are carried to the body cells by the blood.Carbon dioxide from the body cells is carried by the blood to the lungs where it is released into the air. The processof getting oxygen into the body and releasing carbon dioxide is called respiration.

3

www.ck12.org

FIGURE 1.3Being able to control breathing is impor-tant for many activities, such as swim-ming. The man in the photograph is ex-haling before he surfaces from the water.

FIGURE 1.4The bronchi and alveoli. During respi-ration, oxygen gets pulled into the lungsand enters the blood by passing acrossthe thin alveoli membranes and into thecapillaries.

Sometimes breathing is called respiration, but there is much more to respiration than just breathing. There areactually two parts to respiration, external respiration and internal respiration. External respiration is the movementof oxygen into the body and carbon dioxide out of the body. Internal respiration is the exchange of oxygen andcarbon dioxide between the blood and the cells of the body (Figure 1.5).

The Journey of a Breath of Air

Breathing is only part of the process of bringing oxygen to where it is needed in the body. After oxygen enters thelungs, what happens?

4

www.ck12.org Concept 1. The Respiratory System

1. The oxygen enters the blood stream from the alveoli. Then, the oxygen-rich blood returns to the heart.2. Oxygen-rich blood is then pumped through the aorta.3. From the aorta, oxygen-rich blood travels to the smaller arteries and finally to the capillaries.4. The oxygen molecules move out of the capillaries and into the body cells.5. While oxygen moves from the capillaries and into body cells, carbon dioxide moves from the cells into the

capillaries.

FIGURE 1.5Gas exchange is the movement of oxygeninto the blood and carbon dioxide out ofthe blood.

Breathing and Cellular Respiration

The oxygen that arrives at the cells from the lungs is used by the cells to help release the energy stored in molecules ofsugar. Cellular respiration is the process of breaking down glucose to release energy (see the Cell Functions chapter).The waste products of cellular respiration include carbon dioxide and water. The carbon dioxide molecules moveout of the cells and into the capillaries that surround the cells. As explained above, the carbon dioxide is removedfrom the body by the lungs.

Lesson Summary

• Your respiratory system is made up of the tissues and organs that allow oxygen to enter and carbon dioxide toleave your body.

• Respiratory system organs include your nose, mouth, larynx, pharynx, lungs, and diaphragm.• During inhalation, the diaphragm contracts and moves downward, and brings air into the lungs.

During exhalation, the diaphragm and rib muscles relax and air is pushed out of the lungs.

• Oxygen enters the lungs, then passes through the alveoli and into the blood. The oxygen is carried around thebody in blood vessels.

• Carbon dioxide, a waste gas, moves into the blood capillaries and is brought to the lungs to be released intothe air during exhalation.

• The oxygen that arrives from the lungs is used by the cells during cellular respiration to release the energystored in molecules of sugar.

5

www.ck12.org

Review Questions

Recall

1. Name the five main organs in the respiratory system.

2. What is the main function of the respiratory system?

3. In what part of the lung does gas exchange occur?

4. What is the important gas that is carried into the lungs during inhalation?

Apply Concepts

5. A classmate says that lung muscles cause the lungs to move during breathing. Do you agree with your classmate?

6. How do the respiratory system and the cardiovascular system work together?

7. Breathing is an involuntary action. Does this mean that you cannot control your breathing?

8. What is the difference between breathing and respiration?

9. What is the name of the waste gas that is released during exhalation?

Critical Thinking

10. If a disease caused the alveoli to collapse, how might this affect a person’s health?

Further Reading / Supplemental Links

• http://en.wikipedia.org/wiki

Points to Consider

• How do you think the health of your respiratory system might affect the health of other body systems?

References

1. . MSLS-19-01-respiratory-system.2. . MSLS-19-02-Alveoli.3. . MSLS-19-03-breathing-control.4. . MSLS-19-04-alveoli-capillaries.5. . MSLS-19-05-gas-exchange.

6