Facts on File Encyclopedia of Health and Medicine

Structures of the Pulmonary System
TRACHEA lingula (lingular segment)
BRONCHUS lower lobe
bronchiole right lung
ALVEOLUS upper lobe
PLEURA middle lobe
left lung lower lobe
upper lobe DIAPHRAGM

Functions of the Pulmonary System

The LUNGSbring life-giving oxygen into the body
and remove toxic gaseous wastes from it. An
asymmetrical pair, these spongy structures rhyth-
mically expand and compress about 15 to 20
times a minute. Expansion, or inhalation, draws
air and oxygen into the lungs; compression, or
exhalation, expels carbon dioxide and other gases
that are metabolic waste byproducts of cellular
activity. The structures of the nasal cavity and the
upper airway (THROAT) bring air, containing about
21 percent oxygen, into the body. The NOSEand
SINUSESwarm and moisturize the air.
Carrying that air to the lungs are the TRACHEA,
bronchi, and bronchioles—a branching structure of
progressively smaller airways. The air’s destination
is the alveoli, tiny membranous sacs that cluster
grapelike at the ends of the bronchioles. A webbing
of capillaries (tiny blood vessels) surrounds each
ALVEOLUS, carrying erythrocytes (red BLOODcells)
waiting to receive oxygen molecules and release
carbon dioxide molecules. This process, the OXY-
GEN–CARBON DIOXIDE EXCHANGE, gives the body life.

LOBES AND SEGMENTS OF THE LUNGS

Right Lung Left Lung

Right upper lobe Left upper lobe

apical segment apical-posterior segment

posterior segment anterior segment

anterior segment superior lingular segment (lingula)

Right middle lobe inferior lingular segment (lingula)

lateral segment Left lower lobe

medial segment superior segment

Right lower lobe anterior basal segment

superior segment lateral basal segment

anterior basal segment posterior basal segment

medial basal segment

lateral basal segment

posterior basal segment

The lungs: asymmetry in synchronization The

lungs fill the thoracic cavity from neck to

DIAPHRAGMand sternum to spine. Though paired,

the lungs differ somewhat in structure. The right

lung is larger than the left lung, containing three

lobes to the left lung’s two. The left lung must

accommodate the HEART, which nestles into an

indentation called the cardiac notch. Some

anatomists consider the small tail of tissue in the

left lung that drops behind the heart, called the

lingula, as a structure separate from either lobe of

the left lung though most designate it a segment

of the left upper lobe. Each lobe of the lung fur-

ther contains structural divisions called bron-

chopulmonary segments, 10 among the three

THE PULMONARY SYSTEM

The pulmonary system brings oxygen into the body and expels metabolic wastes in the form of gases. Physician special-
ists who treat conditions of the pulmonary system are internists who have subspecialty certifications in pulmonary
medicine (pulmonologists). Physician specialists who operate on the LUNGSand related structures are thoracic sur-
geons. This section, “The Pulmonary System,” presents an overview of the structures and functions of the pulmonary
system, a discussion of pulmonary health and disorders, and entries about the health conditions that can affect the
lungs and related structures.

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