Respiratory System
Breathing Mechanism:
Respiratory Volumes and Capacity,
Alveolar Ventilation, and
Nonrespiratory Movements
Respiratory Volumes
• The different volumes of air that enter or
leave the lungs
– Can be divided into four different volumes:
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Resting tidal volume
Inspiratory reserve volume
Expiratory reserve volume
Residual volume
Spirometry
• Study of respiratory volumes
Spirometer
• Used to measure respiratory air volumes
(except residual volume)
– These volumes can then be used in the evaluation
of respiratory illnesses
Respiratory Cycle
• One inspiration and one expiration
Tidal Volume
• Volume of air that enters or leaves during a
respiratory cycle
Resting Tidal Volume
• Volume of air that enters or leaves during
normal, resting inspiration and expiration
– About 500 mL
Inspiratory Reserve Volume
• Volume of air taken in during forced maximal
inspiration in addition to the resting tidal
volume
– Equals about 3,000 mL
Expiratory Reserve Volume
• Volume of air expelled from the lungs during
maximal forced expiration in addition to the
resting tidal volume
– About 1,100 mL
Residual Volume
• Air that remains in the lungs
– (About 1,200 mL even after the most forceful
expiration)
• Mixes with newly inhaled air
– Prevents the CO2/O2 concentrations from
fluctuating greatly with each breath
Vital Capacity
• The maximum volume of air a person can
exhale after taking the deepest breath
possible
• Equal to tidal volume plus inspiratory reserve
volume plus expiratory reserve volume
– About 4,600 mL
Inspiratory Capacity
• Maximum volume of air a person can inhale
following a resting expiration
• Equal to the tidal volume plus the inspiratory
reserve
– About 3,500 mL
Functional Residual Capacity
• Volume of air that remains in the lungs
following a resting expiration
• Equal to the expiratory reserve volume plus
the residual volume
– About 2,300 mL
Total Lung Capacity
• Equal to the vital capacity plus the residual
volume
– About 5,800 mL
– Total varies with gender, age, and body size
Anatomic Dead Space
• Created by air that is inspired (about 150 mL)
but remains in the trachea, bronchi, and
bronchioles where gas exchange does not
occur
Alveolar Dead Space
• Created by nonfunctional air sacs (due to poor
blood flow in adjacent capillaries)
Physiological Dead Space
• Total volume of the anatomical dead space
and the alveolar dead space
– Volume is essentially the same as the volume of
the anatomical dead space (about 150 mL)
Minute Ventilation
• Volume of air moves into the respiratory
passages each minute
• Equal to the tidal volume multiplied by the
breathing rate
• Much of this new air remains in physiological
dead space
Alveolar Ventilation Rate
• Volume of new air that reaches the alveoli and
is available for gas exchange
• Equal to (the tidal volume minus the
physiological dead space) multiplied by the
breathing rate
– (500 mL – 150 mL) x 12 breaths/min = 4,200
mL/min
Nonrespiratory Air Movements
• Air movements that occur in addition to
breathing
• Used to clear air passages or to express
emotions
• Usually result from reflexes but can also be
triggered through conscious effort
Coughing
• Used to clear the lower respiratory passages
• Involves:
– Taking a deep breath
– Closing the glottis
– Forcing air upward from the lungs against closure
– Suddenly opening the glottis
– And forcing a blast of air upward from the lower
respiratory tract
Sneezing
• Clears the upper respiratory passages
• Usually triggered by an irritant in the lining of
the nasal cavity
• Similar to a cough but in the process of
sneezing the uvula is depressed directing the
upward forced air to enter the nasal passages
Laughing
• Involves a person taking a breath and
releasing it in a series of short expirations
Crying
• Works through the same process as laughing
Hicupping
• Caused by a sudden inspiration due to a
spasmodic contraction of the diaphragm while
the glottis is closed
• Associated noise is caused by air striking the
vocal cords
• Function of hiccups is not known
Yawning
• A deep inspiration that involves the glottis and
mouth being open
• Why we yawn and why it is “contagious” are
not understood