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General design
sensors and afferent fibers
control center
efferent fibers and effectors
Brainstem respiratory centers
pontine respiratory group
pneumotaxic center
“off-switch” for inspiration
apneustic center
integrates inspiratory cutoff information
medullary respiratory centers
dorsal respiratory group
“upper motor neurons” for inspiration
ventral respiratory group
mixed functioning for inspiration and expiration
Chemical control of respiration
chemoreceptors
central chemoreceptors
responsive to changes in arterial PCO2
peripheral chemoreceptors
responsive to changes in arterial PO2, PCO2, [H+]
the drive for ventilation — PaCO2
its advantages
central chemoreceptors
located on ventral medulla
bathed in CSF
CO2 + H2O → H2CO3 → H+ + HCO3–
CSF H+ stimulate medullary chemoreceptors
adaptation of central chemoreceptors
HCO3– transport across blood-brain barrier buffers CSF H+
hypercapnia
hypocapnia
chronic CO2 retention
peripheral chemoreceptors
carotid bodies
glossopharyngeal afferents
high blood flow rates
oxygen consumption
signaling threshold
aortic bodies
vagal afferents
responses
responses to [H+]
in CSF
metabolic acidosis
responses to PaCO2
hypoxia
Other receptors
Hering-Breuer reflex
slow adapting stretch receptors
stimulation helps terminate inspiration
further stimulation activates expiratory neurons
under “normal” conditions
in infants
in exercise
in chronic lung disease
rapidly adapting stretch receptors
mechanical and chemical irritation
J-receptors
respond to increased interstitial volumes
peripheral receptor stimulation
hyperpnea
Cortical override
Issues with control
Cheyne-Stokes respiration
Biot’s respirations
Kussmaul respirations
| Questions for thought | ||
|---|---|---|
| 1. | Describe the reaction of chemoreceptors to changes in arterial oxygen content. | |
| 2. | Describe the Hering-Breuer reflex, what receptors are involved in its operation, and its physiological significance in respiratory control. | |
| 3. | What is the functional difference between the dorsal respiratory group (DRG) and the ventral respiratory group (VRG) of the brainstem? | |
| 4. | You administer supplemental oxygen to a patient with COPD disease, and the patient stops breathing. Why might this happen? | |
| 5. | Discuss the effects of hyperventilation on blood oxygen, carbon dioxide, and pH. | |
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