HUMAN BIOLOGY

178 ChapteR 10

the respiratory system: Built for Gas Exchange

A septum (wall) of bone and cartilage separates the nasal

cavity’s two chambers. Channels link the cavity with

paranasal sinuses above and behind it (which is why

nasal sprays can relieve mucus-clogged sinuses). Tear

glands produce moisture that drains into the nasal cav-

ity. Crying increases the flow, which is why your nose

runs when you cry.

From the nasal cavity, air moves into the pharynx. This

is the entrance to both the larynx (an airway) and the

esophagus (which leads to the stomach). Nine pieces of car-

tilage form the larynx. One of these, the thyroid cartilage,

is the Adam’s apple.

n Getting oxygen from air and releasing carbon dioxide

wastes are the basic functions of the respiratory system.

airways are pathways for moving air

Your lungs and airways make up your respiratory

system (Figure 10.1). During quiet breathing (as while

reading), air typically enters and leaves the system by

way of the nose. Hairs at the entrance to the nasal cav-

ity and in its ciliated epithelial lining filter out large

particles, such as dust, from incoming air. The air also is

warmed in the nose and picks up moisture from mucus.

Oral cavity (mouth)

Supplemental airway when

breathing is labored

Epiglottis

Closes off larynx during swallowing

Pleural membrane

Double-layer membrane with

a fluid-filled space between

layers; keeps lungs airtight

and helps them stick to chest

wall during breathing

Lung (one of a pair)

Lobed, elastic organ of breathing; enhances

gas exchange between internal environment

and outside air

Intercostal muscles
At rib cage, skeletal muscles
with roles in breathing.
There are two sets of
intercostal muscles
(external and internal)

Diaphragm
Muscle sheet between the
chest cavity and abdominal
cavity with roles in breathing

Nasal cavity

Chamber in which air is moistened, warmed,

and filtered, and in which sounds resonate

Pharynx (throat)

Airway connecting nasal cavity and mouth with larynx;

enhances sounds; also connects with esophagus

Larynx (voice box)

Airway where sound is produced; closed

off during swallowing

Trachea (windpipe)

Airway connecting larynx with two

bronchi that lead into the lungs

Bronchus (one of two)

Airway branching from the trachea and

entering lung

Bronchial tree

Increasingly branched airways starting

with two bronchi and ending at air sacs

(alveoli) of lung tissue

A Human respiratory system

BC

bronchiole

alveoli

alveolar sac

(sectioned)

alveolar duct

alveolar

sac

pulmonary

capillary

Figure 10.1 Animated! The respiratory system includes the lungs and airways. Also shown are the diaphragm and other

structures with secondary roles in respiration. (© Cengage Learning)

10.1

Copyright 2016 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).