Unit Seven: Respiration

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 locatedbilaterally 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 medullaAnd mainly causes expiration

c. Pneumotaxic center- in the pons and controlsrate and depth of breathing

Respiratory Center (cont.)

• Dorsal Respiratory Group

a. Sensory termination of the vagal and glosso-pharyngeal nerves, sensory reception from

1. Peripheral chemoreceptors2. Baroreceptors3. Several types of receptors in the lungs

Respiratory Center (cont.)

• Rhythmical Inspiratory Discharges from the

Dorsal Respiratory Group- emits repetitive bursts of inspiratory

neuronalaction potentials

• Inspiratory “Ramp” Signal

a. Inspiratory signal is weak at firstb. Strength increases steadily in 5

second incrementsc. 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 sothat 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 ofInspiration and Increases the Respiratory Rate-primary 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-HeringBreuer Reflex

a. When the lung becomes over inflated, stretch receptors activate a negative feedback responsethat “switches-off” the inspiratory ramp and stopsfurther inspiration

b. In humans the tidal volume increases to more than3x 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 notaffected 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 alveolarventilation when arterial carbon dioxide and hydrogen ion concentration remainnormal

Fig. 41.6

Peripheral Chemoreceptor System (cont.)

• Chronic Breathing of Low Oxygen Stimulates Respiration Even More—”Acclimatization”

a. Exposed to low oxygen, the respiratory centerloses about 80% of its sensitivity

b. When first exposed, a 70% increase in ventilationoccurs

c. After 2-3 days, the increase is 400-500%

Peripheral Chemoreceptor System (cont.)

• Composite Effects of PCO2, pH and PO2 on AlveolarVentilation

Fig. 41.7

Factors That Affect Respiration

• Voluntary control• Irritant receptors in the airways• Brain edema depresses the respiratory center• Anesthesia• Periodic breathing• Sleep apnea