cells and tissues. Finally, substances in cigarette smoke
stimulate uncontrolled cellular growth in the lungs; lung
cancer is the leading cause of cancer deaths in the United
States among both males and females.
role do peripheral chemoreceptors have in
are the consequences of COPD?
the respiratory system's response to exercise?
is the primary change in the respiratory
system with age?
Respiratory Organs Move Air and Exchange
• As shown, the upper respiratory tract consists of the nose
nasal epithelium, and pharynx; it warms, filters, and hu-
midifies incoming air, detects smells in that air, and expels
mucus from the respiratory tract.
Breathing Involves Changes in Pressures
and Volumes 376
• When the respiratory muscles contract during inhalation,
as shown, they expand the thoracic cavity and stretch the
lungs, increasing the volume of the lungs and decreasing the
pressure in the lungs relative to atmospheric pressure. Air
flows into the lungs in response to this change in pressure. In
contrast, when the respiratory muscles relax during exhala-
tion, the opposite events occur, and air flows out of the lungs
Deep breaths and forced exhalations use additional muscles.
T he respiratory sy ste m • Figure 13.1
• The lower respiratory tract consists of a series of branch-
ing tubes that direct air into the lungs. The tubing includes
the larynx, trachea, bronchi, and bronchioles—ending at
the alveoli. The larynx serves as the entrance to the airways
and produces sounds. The epiglottis is part of the larynx
that covers the trachea during swallowing so that food
does not enter the airways. The lungs are enclosed in the
pleural cavity and surrounded by a pleural membrane.
They adhere to the thoracic wall, which moves to draw air
in and push it out. Within the lungs are tiny air sacs called
alveoli, where gas exchange occurs between the lungs and
the blood. •
• The functions of the respiratory system include gas ex-
change, regulation of blood pH, production of sounds, and
excretion of water vapor and heat. The respiratory system
also houses the receptors for smell.
T he b reath in g p ro cess • Figure 1 3 .3
Atmospheric pressure =
Atmospheric pressure =
• Beyond the volume of air flowing into and out of the lungs
during normal quiet breathing (tidal volume), the lungs
are capable of expanding or collapsing to various volumes.
These volumes and capacities are measured with a spi-
rometer during a pulmonary function test and are used to
diagnose various respiratory diseases.
• There are two major types of breathing: costal breathing
(shallow chest breathing) and diaphragmatic breathing
392 CHAPTER 13
The Respiratory System