Chemoreceptors responses

Chemoreceptor response to decreased arterial P02. Hypoxia has a direct depressant effect on central chemoreceptors as well as on the medullary respiratory center. In fact, hypoxia tends to inhibit activity in all regions of the brain. Therefore, the ventilatory response to hypoxemia is elicited only by the peripheral chemoreceptors. 

Table 17.2 Chemoreceptor Responses to Changes in Arterial P02, PC02, and H Ion Concentration...

Chemoreceptor response to increased arterial hydrogen ion concentration. An increase in arterial hydrogen ion concentration, or a decrease in arterial pH, stimulates the peripheral chemoreceptors and enhances ventilation. This response is important in maintaining acid-base balance. For example, under conditions of metabolic acidosis, caused by the accumulation of acids in the blood, the enhanced ventilation eliminates carbon dioxide and thus reduces the concentration of H+ ions in the blood. Metabolic acidosis may occur in patients with uncontrolled diabetes mellitus or when tissues become hypoxic and produce lactic acid. An increase in arterial hydrogen ion concentration has no effect on the central chemoreceptors. Hydrogen ions are unable to cross the blood-brain barrier. 

Serotonin directly causes the contraction of vascular smooth muscle, mainly through 5-HT2 receptors. In humans, serotonin is a powerful vasoconstrictor except in skeletal muscle and heart, where it dilates blood vessels. At least part of this 5-HT-induced vasodilation requires the presence of vascular endothelial cells. When the endothelium is damaged, coronary vessels constrict. As noted previously, serotonin can also elicit reflex bradycardia by activation of 5-HT3 receptors on chemoreceptor nerve endings. A triphasic blood pressure response is often seen following injection of serotonin in experimental animals. Initially, there is a decrease in heart rate, cardiac output, and blood pressure caused by the chemoreceptor response. After this decrease, blood pressure increases as a result of vasoconstriction. The third phase is again a decrease in blood pressure attributed to vasodilation in vessels supplying skeletal muscle. Pulmonary and renal vessels seem especially sensitive to the vasoconstrictor action of serotonin. 

Respiratory depression Barbiturates suppress the hypoxic and chemoreceptor response to CO2, and overdosage is followed by respiratory depression and death. 

Erhan B, Mulligan S, Lahiri S. 1981. Metabolic regulation of aortic chemoreceptor response to CO2. Neurosci Lett 24 143-147. 

Mulligan E, Lahiri S. 1982. Separation of carotid body chemoreceptor responses to O2 and CO2 by oligomycin and by antimycin A. Am J Physiol 242 C200-C206. 

The peripheral (arterial) chemoreceptors response to changes in PaC02 maybe modeled by linear first-order dynamics [BeUville et al., 1979]... 

Marchal F, Bairam A, Haouzi P, Crance JP, Di Giulio C, Vert P, Lahiri S. Carotid chemoreceptor response to natural stimuli in the newborn kitten. Respir Physiol 1992 87 183-193. 

Carroll JL, Bamford OS, Fitzgerald RS. Postnatal maturation of carotid chemoreceptor responses to O2 and CO2 in the cat. J Appl Physiol 1993 75 2383-2391. 

Katz-Salamon M, Jonsson B, Lagercrantz H. Blunted peripheral chemoreceptor response to hyperoxia in a group of infants with bronchopulmonary dysplasia. Pediatr Pulmonol 1995 20 101-106. 

In every species studied to date, the carotid chemoreceptor response to hypoxia increases with postnatal age. In in vitro carotid body preparations, the peak nerve discharge in response to a potent hypoxia stimulus increases about fourfold in neonatal rats during the first month, with most of that change occurring by 2 weeks (10,12,45) (Fig. 2). Similar patterns of postnatal maturation of carotid sinus nerve... 

Mulligan E, Lahiri S. Cat carotid body chemoreceptor responses before and after nicotine receptor blockade with alpha-bungarotoxin. J Auton Nerv Syst 1987 18(1) 25-31. 

Mills E, Jobsis FF. Mitochondrial respiratory chain of carotid body and chemoreceptor response to changes in oxygen tension. J Neurophysiol 1972 35 405-428. 

Nishi K, Okajima Y, Ito H, Sugahara K. Alteration of chemoreceptor responses and ultiastructural features of ischemic carotid body of the cat. Jpn J Physiol 1981 31 677-694. 

Vardhan A, Kachroo A, Sapm HN. Excitatory amino acid receptors in commissural nucleus of the NTS mediate carotid chemoreceptor responses. Am J Physiol 1993 264 R41-R50. 

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