Chapter41: Regulation of Respiration
Guyton and Hall, Textbook of Medical Physiology, 12 edition
Respiratory Center
Fig. 41.1 Organization of the Respiratory Center
Respiratory Center (cont.)
• Composed of several groups of neurons located
bilaterally in the medulla oblongata and pons
• Three major collections of neurons
a. Dorsal respiratory group-in the dorsal medulla
and mainly causes respiration
b. Ventral respiratory group- in the ventral medulla
And mainly causes expiration
c. Pneumotaxic center- in the pons and controls
rate and depth of breathing
Respiratory Center (cont.)
• Dorsal Respiratory Group
a. Sensory termination of the vagal and glossopharyngeal nerves, sensory reception from
1. Peripheral chemoreceptors
2. Baroreceptors
3. Several types of receptors in the lungs
Respiratory Center (cont.)
• Rhythmical Inspiratory Discharges from the
Dorsal Respiratory Group- emits
repetitive bursts of inspiratory neuronal
action potentials
• Inspiratory “Ramp” Signal
a. Inspiratory signal is weak at first
b. Strength increases steadily in 5 second
increments
c. Cycle repeats over and over
Respiratory Center (cont.)
d. Two qualities of the ramp are controlled
1. Control of the rate of increase of the signal so
that during heavy respiration, the ramp increases
rapidly to fill the lungs rapidly
2. Control of the limiting point at which the ramp
suddenly ceases; usual method for
Controlling the rate of respiration
Respiratory Center (cont.)
•
Pneumtaxic Center Limits the Duration of
Inspiration and Increases the Respiratory Rateprimary function is to limit respiration and
secondarily increases the rate of breathing
•
Ventral Respiratory Group- functions in both
inspiration and expiration, differs from the dorsal
group in a number of ways
a. Neurons of the VRG remain almost totally inactive
during normal quiet respiration
Respiratory Center (cont.)
b. Neurons do not appear to participate in the
rhythmical oscillation that controls respiration
c. When the respiratory drive exceeds the norm, the
VRG contributes to the extra respiratory drive
d. Involved in both expiration and inspiration
(separate neurons involved)
Respiratory Center (cont.)
•
Lung Inflation Signals Limit Inspiration-Hering
Breuer Reflex
a. When the lung becomes over inflated, stretch
receptors activate a negative feedback response
that “switches-off” the inspiratory ramp and stops
further inspiration
b. In humans the tidal volume increases to more than
3x normal to initiate this reflex
Control of Respiration
•
Direct Chemical Control of the Respiratory Center
Fig. 41.2
Control of Respiration
•
Direct Chemical Control of the Respiratory Center
a. The dorsal, ventral, and pneumotaxic centers are not
affected by carbon dioxide or hydrogen ion levels
b. The chemosensitive area is highly sensitive to
changes in PCO2 and hydrogen ion concentrations
c. Excitation by hydrogen ions is the primary stimulus
(but hydrogen ions do not cross the BBB so less effect
than carbon dioxide in the neural tissues)
Control of Respiration
d. Carbon dioxide stimulates the chemosensitive area;
indirectly by forming carbonic acid which dissociates
into hydrogen and carbonate
e. Decreased stimulatory effect of carbon dioxide after
1-2 days
f. Changes in oxygen have little direct effect on the
control of the respiratory center
Control of Respiration
•
Quantitative Effects of Blood PCO2 and Hydrogen
Ion Concentration on Alveolar Ventilation
Fig. 41.3
Peripheral Chemoreceptor System for
Control of Respiratory Activity
Fig. 41.4 Respiratory control by peripheral chemoreceptors in the
carotid and aortic bodies
Peripheral Chemoreceptor System (cont.)
• Role of Oxygen in Respiratory Control
a. Chemoreceptors are important for detecting
changes in oxygen
b. Most are located in the aortic and carotid
bodies; a few are found in the thoracic and
abdominal areas
c. Decreased oxygen supply stimulates the
receptors
d. Increased carbon dioxide and hydrogen ion
condentration stimulates the receptors
Peripheral Chemoreceptor System (cont.)
Fig. 41.5 Effect of arterial PO2 on impulse rate from the carotid body
Peripheral Chemoreceptor System (cont.)
• Effect of low arterial PO2 to stimulate alveolar
ventilation when arterial carbon dioxide
and hydrogen ion concentration remain
normal
Fig. 41.6
Peripheral Chemoreceptor System (cont.)
• Chronic Breathing of Low Oxygen Stimulates
Respiration Even More—”Acclimatization”
a. Exposed to low oxygen, the respiratory center
loses about 80% of its sensitivity
b. When first exposed, a 70% increase in ventilation
occurs
c. After 2-3 days, the increase is 400-500%
Peripheral Chemoreceptor System (cont.)
• Composite Effects of PCO2, pH and PO2 on Alveolar
Ventilation
Fig. 41.7
Factors That Affect Respiration
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Voluntary control
Irritant receptors in the airways
Brain edema depresses the respiratory center
Anesthesia
Periodic breathing
Sleep apnea