Respiratory System
Control of Breathing
Respiratory Areas
• Groups of neurons in
the brain stem which
control breathing
Respiratory Areas
• Medullary rhythmicity center
– Includes two groups of neurons that extend
throughout the medulla oblongata
• Dorsal respiratory group
– Stimulate muscles for inspiration (primarily the diaphragm)
– Control the depth of inspiration (forceful breathing)
• Ventral respiratory group
– Stimulate other respiratory muscles such as the intercostals
and abdominals
– Some increase inspiration and some increase expiration
– Control the basic rhythm of breathing
Respiratory Areas
• Pontine Respiratory Group
– Also located in the brainstem (specifically the
pons)
– Make connections with the medullary rhythmicity
center
Factors Affecting Breathing
• Partial pressure
– The amount of pressure that each gas in air
contributes to the total air pressure
– Proportional to the concentration of the gas
• Ex:
– air consists of 21% oxygen
– Atmospheric pressure of air is 760 HG
– So, .21 x 760 = 160 mm Hg, which is the partial pressure of O2
Factors Affecting Breathing
• Breathing rate and depth are affected by the
partial pressure of oxygen and carbon dioxide
in body fluids, the degree to which lung
tissues are stretched and emotional state.
Factors Affecting Breathing
• Changes in partial pressure of carbon dioxide in the
blood are mainly detected indirectly by
chemoreceptors in the medulla oblongata
– (chemoreceptors actually detect increases in hydrogen
ions that are released when carbonic acid (formed by
carbon dioxide combining with water in the fluid of the
brain) is ionized in the brain)
• Increases in carbon dioxide (either through
breathing in carbon dioxide or as cellular waste)
trigger breathing rate and tidal volume to increase
which increase alveolar ventilation and return the
partial pressure of carbon dioxide to normal
Factors Affecting Breathing
• Changes in partial pressure of oxygen are
detected mainly by peripheral chemoreceptors in
specialized structures (carotid bodies and aortic
bodies) located in the walls of the carotid sinuses
and the aortic arch
• When stimulated these structures send impulses
to the respiratory system which then increases
breathing rate and alveolar ventilation
– This process is not usually triggered until the partial
pressure of oxygen falls below 50% of normal
Factors Affecting Breathing
Factors Affecting Breathing
• Inflation reflex
– Occurs when stretch receptors in the visceral
pleura, bronchioles, and alveoli are stimulated by
stretching of lung tissue
– Sends impulses to the respiratory center which
then shortens the duration of inspiratory
movements
– Prevents overinflation of the lungs during forceful
breathing
Factors Affecting Breathing
• Gasping and rapid breathing are normal
responses to stimuli such as fear, anger, and
excitement
Factors Affecting Breathing
• Because control of respiratory muscles is
voluntary breathing patterns can be
consciously altered
Factors Affecting Breathing
• Hyperventilation
– Rapid and deep breathing
– Lowers the blood carbon dioxide level below
normal
– May result in loss of consciousness due to a
decrease in oxygen supply to the brain