Maintenance of the Body
In emphysema, alveoli enlarge permanently and disintegrate.
Te lungs lose their elasticity, and expiration becomes an active
Chronic bronchitis is characterized by excessive mucus
production in the lower respiratory passageways, which severely
impairs ventilation and gas exchange.
Asthma is a reversible obstructive condition caused by an
immune response that causes its victims to wheeze and gasp for
air as their inﬂamed respiratory passages constrict. It is marked
by acute episodes and symptom-free periods.
±uberculosis, an infectious disease caused by an airborne
bacterium, mainly aﬀects the lungs. Although most infected
individuals remain asymptomatic by walling oﬀ the bacteria
in nodules (tubercles), symptoms appear when immunity is
depressed. Some patients’ failure to complete drug therapy has
produced multidrug-resistant ±B strains.
Lung cancer, promoted by free radicals and other carcinogens, is
extremely aggressive and metastasizes rapidly.
Developmental Aspects of the Respiratory System
Te superior respiratory system mucosa develops from the
invagination of the ectodermal olfactory placodes. Te mucosa
of the inferior passageways develops from an outpocketing of
the endodermal foregut lining. Mesoderm forms the walls of the
respiratory conduits and the lung stroma.
Cystic ﬁbrosis (CF), the most common fatal hereditary disease in
North America, results from an abnormal CF±R protein that fails
to form a chloride channel. Te result is thick mucus, which clogs
respiratory passages and invites infection.
With age, the thorax becomes more rigid, the lungs become
less elastic, and vital capacity declines. In addition, sleep apnea
becomes more common, and respiratory system protective
mechanisms are less eﬀective.
Hypocapnia depresses respiration and results in decreased
ventilation and, possibly, apnea.
levels below 60 mm Hg strongly stimulate peripheral
Decreased pH and a decline in blood P
act on peripheral
chemoreceptors and enhance the response to CO
Emotions, pain, body temperature changes, and other stressors
can alter respiration by acting through hypothalamic centers.
Respiration can also be controlled voluntarily for short periods.
Dust, mucus, fumes, and pollutants initiate pulmonary irritant
Te inﬂation (Hering-Breuer) reﬂex is a protective reﬂex initiated
by extreme overinﬂation of the lungs; it acts to terminate
Respiratory System; Topic: Control of Respiration, pp. 6–14.
As exercise begins, there is an abrupt increase in ventilation
(hyperpnea) followed by a more gradual increase. When exercise
stops, there is an abrupt decrease in ventilation followed by a
gradual decline to baseline values.
, and blood pH remain quite constant during exercise
and hence do not appear to account for changes in ventilation.
Inputs from higher centers and proprioceptors may contribute.
At high altitudes, arterial P
and hemoglobin saturation levels fall
because of the decrease in atmospheric pressure compared to sea
level. Increased ventilation helps restore P
to physiological levels.
Long-term acclimatization involves increased erythropoiesis.
Homeostatic Imbalances of the Respiratory
±wo major respiratory disorders are COPD (emphysema and
chronic bronchitis) and lung cancer; smoking is a signiﬁcant
cause. A third major disorder is asthma. Multidrug-resistant
tuberculosis may become a major public health problem.
Chronic Obstructive Pulmonary Disease
COPD is characterized by an irreversible decrease in the ability to
force air out of the lungs.
(Some questions have more than one correct answer. Select the best
answer or answers from the choices given.)
Cutting the phrenic nerves will result in
air entering the
paralysis of the diaphragm,
the diaphragmatic reﬂex,
paralysis of the epiglottis.
Which of the following laryngeal cartilages is/are not paired?
Under ordinary circumstances, the inﬂation reﬂex is initiated
the ventral respiratory group,
overinﬂation of the alveoli and bronchioles,
Te detergent-like substance that keeps the alveoli from
collapsing between breaths because it reduces the surface tension
of the water ﬁlm in the alveoli is called
Which of the following determines the direction of gas
solubility in water,
partial pressure gradient,
molecular weight and size of the gas
When the inspiratory muscles contract,
the size of the
thoracic cavity increases in diameter,
the size of the thoracic
cavity increases in length,
the volume of the thoracic cavity
the size of the thoracic cavity increases in both
length and diameter.