Peripheral Chemoreceptors Respond to Po2 Pco2 and pH

Peripheral chemoreceptors are located in the carotid and aortic bodies and detect changes in arterial blood Po2, Pco2, and pH. Carotid bodies are small (~ 2 mm wide) sensory organs located bilaterally near the bifurcations of the common carotid arteries near the base of the skull. Afferent nerves travel to the CNS from the carotid bodies in the glos-

sopharyngeal nerves. Aortic bodies are located along the ascending aorta and are innervated by vagal afferents.

As with the medullary chemoreceptors, increasing Paco2 stimulates peripheral receptors. H+ formed from H2CO3 within the peripheral chemoreceptors (glomus cells) is the stimulus and not molecular CO2. About 40% of the effect of Paco2 on ventilation is brought about by peripheral chemoreceptors, while central chemoreceptors bring about the rest. Unlike the central sensor, peripheral chemoreceptors are sensitive to rising arterial blood H+ and falling Po2. They alone cause the stimulation of breathing by hypoxia; hypoxia in the brain has little effect on breathing unless severe, at which point breathing is depressed.

Carotid chemoreceptors play a more prominent role than aortic chemoreceptors; because of this and their greater accessibility, they have been studied in greater detail. The discharge rate of carotid chemoreceptors (and the resulting minute ventilation) is approximately linearly related to Paco2. The linear behavior of the receptor is reflected in the linear ventilatory response to carbon dioxide illustrated in Figure 22.6. When expressed using pH, the response curve is no longer linear but shows a progressively increasing effect as pH falls below normal. This occurs because pH is a logarithmic function of [H + ], so the absolute change in [H + ] per unit change in pH is greater when brought about at a lower pH.

The response of peripheral chemoreceptors to oxygen depends on arterial Pao2, and not oxygen content. Therefore, anemia or carbon monoxide poisoning, two conditions that exhibit reduced oxygen content but have normal Pao2, have little effect on the response curve. The shape of the response curve is not linear; instead, hypoxia is of increasing effectiveness as Po2 falls below about 90 mm Hg. The behavior of the receptors is reflected in the ventilatory response to hypoxia illustrated in Figure 22.7. The shape of the curve relating ventilatory response to Po2 resembles that of the oxyhemoglobin equilibrium curve when plotted upside down (see Chapter 21). As a result, the ventilatory response is inversely related in an approximately linear fashion to arterial blood oxygen saturation.

The nonlinearities of the ventilatory responses to Po2 and pH, and the relatively low sensitivity across the normal ranges of these variables, cause ventilatory changes to be apparent only when Po2 and pH deviate significantly from the normal range, especially toward hypoxemia or acidemia. By contrast, ventilation is sensitive to Pco2 within the normal range, and carbon dioxide is normally the dominant chemical regulator of breathing through the use of both central and peripheral chemoreceptors (compare Figs. 22.6 and 22.7).

There is a strong interaction among stimuli, which causes the slope of the carbon dioxide response curve to increase if determined under hypoxic conditions (see Fig. 22.6), causing the response to hypoxia to be directly related to the prevailing Pco2 and pH (see Fig. 22.7). As discussed in the next section, these interactions, and interaction with the effects of the central carbon dioxide sensor, profoundly influence the integrated chemoresponses to a primary change in arterial blood composition.

Carotid and aortic bodies also can be strongly stimulated by certain chemicals, particularly cyanide ion and other poisons of the metabolic respiratory chain. Changes in blood pressure have only a small effect on chemorecep-tor activity, but responses can be stimulated if arterial pressure falls below about 60 mm Hg. This effect is more prominent in aortic bodies than in carotid bodies. Afferent activity of peripheral chemoreceptors is under some degree of efferent control capable of influencing responses by mechanisms that are not clear. Afferent activity from the chemoreceptors is also centrally modified in its effects by interactions with other reflexes, such as the lung stretch reflex and the systemic arterial baroreflex (see Chapter 18). Although the breathing interactions are not well understood in humans, they serve as examples of the complex interactions of cardiorespiratory regulation. Interactions among chemoreflexes, however, are easily demonstrated.

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  • cara
    Do central chemoreceptors respond to po2?
    8 years ago
  • manuela
    What describes a chemoreceptor response to po2?
    8 years ago
  • Gorbulas
    What is carotid and aortic bodies?
    8 years ago
  • andrew
    Which chemoreceptors would respond to co poisoning?
    8 years ago
  • maura
    Why can peripheral chemoreceptors be relatively insensitive to changes in arterial o2 levels?
    8 years ago
  • Gisella
    Is peripheral chemoreceptors or central chemoreceptors more sensitive to changes in arterial pCO2?
    8 years ago
  • leah theissen
    Which receptors are responsible for detecting changes in arterial po 2?
    8 years ago
  • Petra
    What change in the blood peripheral chemoreceptors respond?
    8 years ago
  • harri
    Why arent central chemoreceptors sensitive to changes in arterial pH?
    8 years ago
  • sebastian p
    Why are co2 sensors located in the carotid artery?
    8 years ago
  • Jaana
    When the PaO2 falls below what, there is suppression of the peripheral chemoreceptors?
    8 years ago
  • hagos
    Why are co2 receptors located in the aorta and carotid arteries?
    7 years ago
  • Viola
    What is the ventilatory response to changes in pco2 and po2?
    7 years ago
  • sanna-leen
    Why do peripheral chemoreceptors respond to pAO2?
    7 years ago
  • lucie
    Is respiratory control more sensitive to small changes in arterial Po2 or in artrial Pco2?
    7 years ago
    Where Are Peripheral Chemoreceptors Located?
    6 years ago
  • catherine
    Why are the peripheral chemoreceptors suppressed under arterial oxygen pressures of 30 torr?
    6 years ago
  • caoimhe
    Is a skeletal muscle a chemoreceptor?
    5 years ago
  • johnnie reif
    How changes of po2 and pco2 affect peripheral and centeral chemorecptors?
    5 years ago
  • iivari
    What effect did PCO2 , PO2 and H have on the chemoreceptors, when at rest?
    4 years ago
    Why does co poisoning and anaemia not affect peripheral chemoreceptors?
    4 years ago
  • semolina
    Why carotid chemoreceptors are not stimulated in anaemia?
    4 years ago
  • anke
    Why perpheral chemoreceptors are not stimulated in anemia?
    4 years ago
  • Asmara
    Why carotid chemoteceptors are not stimulated in anaemia?
    4 years ago
  • karla
    Does co2 or h effect on peripheral chemoreceptor?
    3 years ago
  • aatifa
    Why carotid body not stimulated by anemic hypoxia?
    3 years ago
  • raija kurri
    Why peripheral chemoreceptor not respond to CO poisoning?
    3 years ago
  • Anja
    Why only anaemic hypoxia not stimulate peripheral chemoreceptors?
    3 years ago
  • Alem
    Why peripheral chemoreceptors nt affected in anemia?
    3 years ago
  • Ernest
    Which of the following not stimulate peripheral chemoreceptor?
    3 years ago
  • amy russell
    Why is that peripherAl chemoreceptor can assist an anaemia patient?
    3 years ago
  • bernd
    Which receptors will detect the increase in pco2 and decrease in po2 in the blood?
    3 years ago
  • abraham
    Which receptors will detect the increas in pco2?
    3 years ago
  • Hiewan
    How do the change in PO2 detected?
    3 years ago
  • primula
    Which receptors will detect the increases in PCO2 and a decrease in PO2?
    3 years ago
  • pearl bunce
    Which receptors will.detect inreasease of pco2 and decrease in po2?
    3 years ago
  • Asmeret
    Which Receptors Will Detect The increase in PCO2 and Decreases in PO2 in the blood?
    3 years ago
  • morgana
    Which receptor will detect increase of pco2?
    3 years ago
  • welde
    Which receptors will detect the increases in PCO2 and decrease in PO2 in the blood?
    3 years ago
  • Salvatore
    Why there is no stimulation of chemoreceptor only in anaemic hypoxia?
    2 years ago
  • milo
    Why carotid body is not stimulated in anaemic hypoxia?
    2 years ago
  • Allie Kelly
    How many % of pco2 affect in peripheral chemorecptor?
    2 years ago
  • S
    Why anemia hypoxia does not stimulate peripheral chemoreceptor?
    2 years ago
  • juliane
    Why anemic hypoxia does not stimulate chemoreceptors?
    2 years ago
  • helen
    How pco2 and H afeect periphera chemoreceptor?
    2 years ago
  • halfred whitfoot
    Do peripheral chemoreceptors respond to the increase of carbon dioxide and hydrogen ions?
    2 years ago
    Can anemic hypoxia be an effective stimulus for chemoreceptors in carotid body?
    2 years ago
  • Aila
    How chemoreptors influence by arterial CO2?
    1 year ago
  • Dollie
    Can carotid body chemoreceptors detect carbon monoxide poisoning?
    1 year ago
  • magnus pulkkinen
    Why the Pco2 is more sensitivity in minute ventilation?
    1 year ago
    Do aortic and carotid body receptors sense po2?
    1 year ago
  • fulvus
    Why more sensitive to δpaco2than to δpao2?
    1 year ago
  • Selamawit
    Where is the primary sensor CO2 located and how are changes in pCO2 detected by this sensor?
    1 year ago
  • jonas
    Which chemoreceptors responds to low PO2?
    1 year ago
  • medhane
    Which chemoreceptors respond to decreased PO2?
    1 year ago
  • ulrike
    What happens when carotid chemoreceptors are activated?
    10 months ago
  • murron
    Where is the primary sensor for CO2 located and how are changes i npCO2 detected by this sensor?
    8 months ago
  • codi
    What receptor Detect and response to changes in PO2 in the carotid artery and aorta?
    8 months ago
  • madihah
    DO peripheral chemoreceptors sense pH and C02?
    7 months ago
  • aaran
    Is the chemoreceptor reflex in lungs sensitive to nitrogen?
    6 months ago
  • Michael Shaw
    How reduced oxygen triggers chemoreceptors?
    4 months ago

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