Maintenance of the Body
What is the underlying defect in cystic ﬁbrosis?
List two reasons for the decline in vital capacity seen with
For answers, see Appendix H.
Lungs, bronchial tree, heart, and connecting blood vessels—
together, these organs fashion a remarkable system that oxygen-
ates blood, removes carbon dioxide, and ensures that all tissue
cells have access to these services. Although the cooperation of
the respiratory and cardiovascular systems is obvious, all organ
systems depend on the functioning of the respiratory system, as
on p. 843.
Te number of glands in the nasal mucosa decreases as does
blood ﬂow to this mucosa. For this reason, the nose dries and
produces a thick mucus that makes us want to clear our throat.
Additionally, many of the respiratory system’s protective mecha-
nisms become less eﬀective with age. Mucosal cilia are less ac-
tive, and the macrophages in the lungs become sluggish. Te
net result is that the elderly are more at risk for respiratory tract
infections, particularly pneumonia and inﬂuenza.
Check Your Understanding
What distinguishes the obstruction in asthma from that in
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Respiration involves four processes: pulmonary ventilation,
external respiration, transport of respiratory gases in the blood,
and internal respiration. Both the respiratory system and the
cardiovascular system are involved in respiration.
Functional Anatomy of the Respiratory System
Respiratory system organs are divided functionally into conducting
zone structures (nose to terminal bronchioles), which ﬁlter,
warm, and moisten incoming air; and respiratory zone structures
(respiratory bronchioles to alveoli), where gas exchanges occur.
The Nose and Paranasal Sinuses
Te nose provides an airway for respiration; warms, moistens,
and cleanses incoming air; and houses the olfactory receptors.
Bone and cartilage plates shape the external nose. Te nasal cavity,
which opens to the exterior, is divided by the nasal septum. Paranasal
sinuses and nasolacrimal ducts drain into the nasal cavities.
Te pharynx extends from the base of the skull to the level of
. Te nasopharynx is an air conduit; the oropharynx and
laryngopharynx are common passageways for food and air.
±onsils are found in the oropharynx and nasopharynx.
Te larynx, or voice box, contains the vocal folds (cords). It also
provides a patent airway and serves as a switching mechanism to
route food and air into the proper channels.
Te epiglottis prevents food or liquids from entering the
respiratory channels during swallowing.
Te trachea extends from the larynx to the main bronchi.
C-shaped cartilage rings reinforce the trachea and keep the
trachea patent. Its mucosa is ciliated.
The Bronchi and Subdivisions
Te right and le² main bronchi run into their respective lungs,
within which they subdivide into smaller and smaller passageways.
Te terminal bronchioles lead into respiratory zone structures:
respiratory bronchioles, alveolar ducts, alveolar sacs, and ﬁnally
alveoli. Gas exchange occurs in the alveoli, across the respiratory
As the respiratory conduits become smaller, the amount of
cartilage decreases and is ﬁnally lost; the mucosa thins, and
smooth muscle in the walls increases.
Respiratory System; Topic: Anatomy Review:
Respiratory Structures, p. 6.
The Lungs and Pleurae
Te lungs, the paired organs of gas exchange, ﬂank the
mediastinum in the thoracic cavity. Each is suspended in pleurae
via its root and has a base, an apex, and medial and costal
surfaces. Te right lung has three lobes; the le² has two.
Te lungs are primarily air passageways/chambers, supported by
an elastic connective tissue stroma.
Te pulmonary arteries carry deoxygenated blood returned
from the systemic circulation to the lungs, where gas exchange
occurs. Te pulmonary veins return newly oxygenated (and
most bronchial venous) blood back to the heart to be distributed
throughout the body. Te bronchial arteries provide the nutrient
blood supply of the lungs.
Te parietal pleura lines the thoracic wall and mediastinum; the
visceral pleura covers external lung surfaces. Pleural ﬂuid reduces
friction during breathing movements.
Respiratory System; Topic: Anatomy Review:
Respiratory Structures, pp. 1–5.
Mechanics of Breathing
Pressure Relationships in the Thoracic Cavity
Intrapulmonary pressure is the pressure within the alveoli.
Intrapleural pressure is the pressure within the pleural