Regulation of Respiration
Regulation of respiration
• Nervous system adjusts ventilation to meet demand of
the body
• PO2/ and PCO2 are hardly altered even during stress
and exercise
The respiratory center
• Dorsal respiratory group
• Ventral respiratory group
• Pneumotaxic center
Dorsal respiratory group
• Extends the length of the medulla
• Neurons in the tractus solitarius
• Generates rhymthical inspiratory discharges
– Origin unknown
• Inspiratory ramp signal
– Not a burst of AP’s but begins weakly and increases steadily for 2
seconds then ceases for 3 seconds
– Produces steady increase in lung volume, not gasps
Pneumotaxic center
• Limits the duration of inspiration
– Controls the “switch off” point of the inspiratory ramp, ends filling
phase
– Strong .5 sec- lungs fill lightly
– Weak 5 seconds – lungs fill greatly
• Increases respiratory rate
– By shortening expiration, and the whole respiratory cycle
– Strong signal can increase the rate 30 – 60 breaths per minute
Ventral respiratory group
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“overdrive”
Functions in both inspiration and expiration
Inactive during normal breathing
Need increased ventilation
– Respiratory signals spill into this center and contribute to respiratory
drive
• Ventral nerve stimulation causes inspiration
• Stimulation of other nerves causes expiration
• Provides powerful expiratory signals to abdominal muscles
during expiration
Ventral respiratory group
• Hering-Breuer inflation reflex
– Stretch receptors in the bronchi and bronchioles pass
impulses through the vagi to the dorsal respiratory group
– Lungs over stretch – respiratory ramp switched off
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Chemical control over respiration
Chemosensitive area of the respiratory center
Sensitive to CO2 or H+
Other centers don’t detect them
Excites other portions of the respiratory center
Chemical control over respiration
• Excess CO2 and H+ stimulate the respiratory center
• Causes increased strength of inspiration and expiration signals to the
respiratory muscles
• O2 has no direct effect on the respiratory center
Chemical control over respiration
• CO2 exerts its effect through conversion to bicarbonate and H+
• CO2 crosses the blood brain barrier (H+ does not)
• PCO2 in blood increases, PCO2 in the interstitial fluid increases, PCO2 in
the CSF increases
• Blood PCO2 has great effect on alveolar ventilation (30-60 mm Hg)
Peripheral control over respiratory
activity
Peripheral chemoreceptors for O2
• Some detect CO2 and H+
• Receptors transmit signals to the respiratory center
•
– Carotid bodies
– Aortic bodies
Peripheral control over respiratory
activity
Role of O2 in Peripheral
Respiratory Control
• Decreased O2 has no direct effect on respiratory center
• Effect is through discharges from the chemoreceptors
• Low PO2 stimulates aortic and carotid chemoreceptors,
increases respiratory rate, PCO2 goes down and them slows the
rate
• CO2 and H+ effect chemoreceptors but the effect is minimal
compared to their effects in the respiratory center
• Fig 29-5
Role of O2 in Peripheral
Respiratory Control
Exercise and respiratory control
• Figure 29-6
Exercise and respiratory control
• During exercise
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O2 consumption and CO2 formation increase 20X
Alveolar ventilation increases in step with increased metabolism
PO2, PCO2 and pH remain normal
Brain stimulates the respiratory center along with contracting muscles
Prioreceptors transmit excitatory impulses to the respiratory center
Pulmonary abnormalities
• Chronic pulmonary emphysema
– Chronic infection-chronic obstruction-entrapment of air in
alveoli- increased airway resistance and decreased diffusing
capacity of the lung-
• Pneumonia
Pulmonary abnormalities
– Inflammatory condition of the lung
– Alveoli fill with fluid and blood cells
– Alveolar membrane is infected with bacteria and becomes
porous to fluid and cells
• Pneumonia
Pulmonary abnormalities
• Collapse of alveoli
Atelectasis
– Airway obstruction
– Lack of surfactant
Asthma
• Spastic contraction of smooth muscle in the bronchioles
• Hypersensitivity of bronchioles to substances in the air
– IgE attached to mast cells interact with antigen and produce histamine,
SRS-A, and eosionphilic chemotactic factor, and bradykinin
– Edema, mucus production, and spasms of bronchiolar smooth muscle
results