relax, the thoracic cavity returns to its resting size
and the lungs expel air.
With each breath the EPIGLOTTIS, a flap of carti-
laginous tissue at the back of the throat, opens
and closes like a valve to allow air to pass in and
out of the trachea and to keep other substances
(such as saliva, food, and drink) from entering the
trachea and lungs. With the changing of air pres-
sure that occurs between inhalation and exhala-
tion, oxygen molecules migrate through the
micrometers-thin membrane walls of the alveoli
into the blood circulating through the capillaries
that surround the alveoli. Carbon dioxide mole-
cules cross back in exchange. The respiratory cycle
repeats about 20,000 times every 24 hours, vary-
ing in rate according to the body’s oxygen needs.
ALTITUDE AND OXYGEN
Though the percentage of oxygen in the air
remains constant regardless of altitude, the con-
centrationof oxygen molecules decreases as alti-
tude increases. The concentration of oxygen
molecules in the air is greater at sea level than in
the mountains. At a higher altitude the LUNGS
must work harder to extract enough oxygen to
meet the body’s needs. In the short term the body
compensates by raising the RESPIRATION RATE—
breathing faster. After about 72 hours at a higher
altitude, the decreased concentration of oxygen
in the air stimulates the BONE MARROWto produce
more erythrocytes (red BLOOD cells), which
increases the blood’s capacity to carry oxygen.Health and Disorders of the Pulmonary System
The lungs rhythmically pull air into and release air
from the body in a choreography the BRAINcoordi-
nates with the HEART RATEandBLOOD PRESSUREto
maintain the vital supply of oxygen to tissues
throughout the body. Aerobic conditioning
through regular physical exercise, not smoking,
and maintaining healthy weight are among the
key factors that keep the lungs functioning effi-
ciently across the span of life.
Lung capacity peaks during the 20s and gradu-
ally declines with increasing age. People who
remain aerobically fit continue to have strong pul-
monary function despite this decline, as their
lungs still have enough reserve to meet the body’s
needs. People whose lifestyles are sedentary are
more likely to experience a decline in lung capac-
ity, apparent in shortness of breath when climbing
stairs, when walking distances, or with sudden
bursts of physical exertion.
The lungs are subject to few BIRTH DEFECTS. Con-
genital disorders of the lungs include hereditary
disorders, such as CYSTIC FIBROSIS, and conditions
resulting from prematurity or inadequate develop-
ment of the lungs before birth, such as chronic
lung disease of infancy. Cardiovascular anomalies,
notably structural malformations such as transpo-
sition of the great arteries (TPA) or hypoplastic left
heart syndrome (HLHS), affect the integration of
function between the heart and the lungs.
Cigarette smoking, CARDIOVASCULAR DISEASE
(CVD), and long-term exposure to irritants such as
industrial chemicals are the leading causes of
acquired pulmonary disease. Because the lungs
face continual exposure to external pathogens,
they are vulnerable to viral, bacterial, and fungal
invaders. Immune cells—notably lymphocytes,
macro-phages, and neutrophils—reside within the
walls of the bronchi, detecting and eliminating
most pathogens before they can cause localized
INFECTION. However, those that slip through the
body’s defense mechanisms can cause serious dis-
eases such as PNEUMONIA(viral or bacterial).HEALTH CONDITIONS THAT CAN AFFECT
THE STRUCTURES OF THE PULMONARY SYSTEM
ANTHRACOSIS APNEA
ASBESTOSIS ASPERGILLOSIS
ASPIRATION ASTHMA
ATELECTASIS BERYLLIOSIS
BRONCHIECTASIS BRONCHITIS
BYSSINOSIS CHRONIC OBSTRUCTIVE
CYSTIC FIBROSIS PULMONARY DISEASE(COPD)
LEGIONNAIRES’ DISEASE INTERSTITIAL LUNG DISORDERS
LUNG CANCER LUNG ABSCESS
Pneumocystis carinii PLEURISY
PNEUMONITIS PNEUMONIA
PULMONARY EDEMA pulmonary congestion
PULMONARY FIBROSIS PULMONARY EMBOLISM
RESPIRATORY FAILURE PULMONARY HYPERTENSION
tuberculosis SILICOSISInefficient cardiovascular function places signif-
icant strain on pulmonary function, influencing178 The Pulmonary System