Regulation of respiration

The respiratory system supplies O2 and removes carbon dioxide (CO2) over a wide range of metabolic demands. Control is exercised by the respiratory center located in the medulla oblongata and pons. It is divided into three groups of neurons (Fig. 8.8). The dorsal group functions during quiet respiration and also acts as the pacemaker by initiating inspiration. The ventral group is more important during active respiration. The pneumotaxic center responds to stimuli by increasing the rate of respiration.

The respiratory center receives input from higher brain centers and from chemo- and mechanoreceptors. In short, there are two major stimuli to breathe - hypoxia and acidosis. Central chemoreceptors are located in the medulla and are sensitive to acidosis in the form of CO2 (as hydrogen ions can not cross the blood-brain or blood-CSF barriers directly). CO2 crosses the blood-brain and blood-CSF barriers to reach the medulla. The CO2 binds with water and produces hydrogen ions which act on the pacemaker (dorsal group of neurons) and stimulate respiration. Peripheral chemoreceptors are located in the carotid and aortic bodies and respond to a fall in partial pressure of arterial oxygen (PaO2) below 60 mmHg

Figure 8.9. The hemoglobin dissociation curve. Note the effects on pH, DPG, and temperature allowing for alterations in oxygen unloading at a given PO2. A shift of the curve to the right indicates that hemoglobin will remain less saturated for a given PO2.

PO2 (mmHg)

Figure 8.9. The hemoglobin dissociation curve. Note the effects on pH, DPG, and temperature allowing for alterations in oxygen unloading at a given PO2. A shift of the curve to the right indicates that hemoglobin will remain less saturated for a given PO2.

(8kPa). They provide input to the higher brain centers and brainstem to increase respiration. Mechanoreceptors include stretch receptors, irritant receptors, and juxtacapillary (or J) receptors. Stretch receptors inhibit the level of inspiration and juxtacapillary receptors are thought to be important in the sensation of dyspnea.

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