Chemoreceptors and Chemoreceptor Reflexes

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Baroreceptors and Chemoreceptors

Pneumologie Stuttgart, Germany [01 May , 45 Suppl ]. Type: Journal Article.

Abstract 15 patients with obstructive sleep apnea syndrome and arterial hypertension H-OSAS , 25 normotensive patients with sleep apnea syndrome N-OSAS and 20 healthy age-matched controls C were included in this study. Ventilatory responses to activation hypoxia and inactivation hyperoxia of carotid chemoreceptors were studied in all subjects.

Relationship between hypoxic ventilatory reactivity and nocturnal bradycardia during apnea-phases was analysed in both groups of patients. Results and conclusions.

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They rise and fall respectively throughout a breath-hold as we continue to metabolize foodstuffs for energy and the break-point is reached when the P co 2 in arterial blood has risen from its normal value of around 40 mmHg 5. Breath-hold times can therefore be increased by prior hyperventilation which lowers the initial carbon dioxide or by breathing pure oxygen instead of air.

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Combining these two methods will maximally — and dramatically — increase breath-hold times. OK: breathe out, now! These sensors are known as chemoreceptors, and they play a crucial role in acid—base homeostasis and oxygen supply. They help to maintain the appropriate oxygen, carbon dioxide , and pH in the body by initiating a variety of cardiovascular and respiratory reflexes.

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Such reflexes are required not just during breath-holds but whenever these levels are altered by changes in metabolism, changes in environment, or disease — for example during exercise , at high altitude , or during respiratory failure caused by lung disease. Chemoreception occurs both in the brain and in the blood vessels. Any change in blood carbon dioxide is transmitted to the brain: here, as elsewhere, a rise in carbon dioxide increases acidity; the response of the central chemoreceptor mechanism to such a rise is to stimulate breathing, thus tending to correct the change by the loss of more carbon dioxide.

The first descriptions of a small structure, only 5—8 mm long and weighing just a few mg, lying beside the division of the carotid artery in the neck, appeared during the eighteenth century. It was not until that Fernando de Castro, an anatomist working in the Cajal Institute in Madrid, recognized the carotid body as a sensory organ and postulated its function as a chemoreceptor with afferent nerves to the brain.

Chemoreceptor reflex

The sensory function of the carotid and aortic chemoreceptors was confirmed by a series of physiological studies performed around the same time by Jean-Frans Heymans and his son, Corneille, in Ghent , Belgium , for which Corneille received the Nobel prize in Shortly after these discoveries, a series of studies initiated in Japan and continued in the US described how bilateral division of the afferent nerves from the carotid bodies brought relief in a number of sufferers from asthma. Unfortunately, these results could not be confirmed, and a possible mortality attributable to the surgical intervention led to the banning of the procedure.

Chemoreceptor Reflex

Studies following such procedures did however provide evidence that people without carotid body function did not show the normal increase in breathing in response to low oxygen. The carotid body is highly vascular and receives the highest blood flow, relative to its size, of any organ in the body. It is divided into a number of lobules, each containing clusters of two distinct cell types together with arteriolar blood vessels and capillaries, nerve fibres, and a few autonomic ganglion cells.

Type I cells, of which there are tens of thousands in each carotid body, are believed to be the primary transducer elements. A smaller number of Type II cells envelop them and provide a supportive function, like that of glia in the nervous system. Because these features resemble those of the terminal of a nerve fibre, the Type I cell is believed to form the equivalent of a nerve-to-nerve synapse with the sensory nerve endings close to it, generating action potentials in them by the graded release of a transmitter.

In common with almost all synapses, the release of neurotransmitter is dependent upon an elevation in the concentration of ionic calcium within the Type I cell.

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This volume records the papers presented in Warsaw on the meeting of the International Society of Arterial Chemoreception (LS. A. C.) organized as a Satellite. Learn more about Chemoreceptor Reflex The central chemoreceptors are located in the brainstem and respond to changes in pH mediated primarily by.

Peripheral chemoreceptors share with central chemoreceptors a responsiveness to acidity and carbon dioxide, but their uniqueness lies in their ability also to sense lowered oxygen hypoxia in arterial blood. The most likely neurotransmitter released during hypoxia is dopamine , with the other chemicals stored in the Type I cell acting as modulators. This dopamine-secreting action of Type I cells has led to the recent trial use of surgical autografts of carotid body tissue in the treatment of animal models of Parkinson's disease.