The Brain Controls Breathing 386
• As shown, the respiratory center in the medulla and pons
consists of four areas. The inspiratory area controls the rate
of normal quiet breathing. The expiratory area assists in
forceful exhalation. The pneumotaxic area influences the
inspiratory area to shorten the breathing rate. The apneustic
area influences the inspiratory area to slow the breathing
rate.
• The respiratory center is influenced by the cerebral cortex
for voluntary control of breathing, by proprioceptors in mus-
cles and joints activated by physical activity, and by central
and peripheral chemoreceptors stimulated by metabolic
activity.
• Central chemoreceptors in the medulla monitor the pH and
PCO
of the cerebrospinal fluid. Peripheral chemoreceptors
in the aortic arch and carotid bodies monitor the PO
, PCO
,
and pH of the blood. The chemoreceptors feed information
back to the respiratory center to alter the rate and depth of
breathing.
C ontrol o f th e rate and d ep th o f b reath ing
b y th e respiratory ce n te r • Figure 1 3 .7
Pneumotaxic area .
Apneustic area
Inspiratory arei
Expiratory area
^ 5 Good Respiratory Health Is Essential 390
• During exercise, proprioceptors and peripheral chemore-
ceptors modify the respiratory center of the brain, causing
an increase in the rate and depth of breathing to increase
oxygen supply to working muscles. The proprioceptors act
early in this process, when muscles first begin the activity.
The chemoreceptors act later, as levels of metabolic wastes
in the blood begin to increase.
• Aging primarily influences the elasticity of the lungs and
chest wall, which in turn reduces vital capacity. This also
reduces pulmonary gas exchange and may reduce the ability
to do prolonged or strenuous exercise. In addition, elderly
people are susceptible to various respiratory diseases,
including chronic bronchitis, emphysema, and pneumonia.
• As shown, smoking, and aging can reduce the flow of air in
the airways, decrease the elasticity of the lungs and chest,
and lessen pulmonary gas exchange. In addition, respiratory
disease and pulmonary infections such as pneumonia and
tuberculosis can destroy the alveolar membranes and cause
multiple respiratory problems.
• Smoking increases the risk of developing pulmonary diseas-
es such as chronic obstructive pulmonary disease and lung
cancer.
E ffects o f a g in g and sm ok in g on th e respiratory sy ste m •
Figure 1 3 .1 0
Airway flow decreases.
Lung capacity decreases as the
Pulmonary gas exchange is affected,
elasticity of chest and lung tissues
decreasing the level of O2 and increasing
decreases.
the level of CO2 in the blood.
394 CHAPTER 13
The Respiratory System
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