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Altitude, temperature, circadian rhythms and exercise
Published in Adam P. Sharples, James P. Morton, Henning Wackerhage, Molecular Exercise Physiology, 2022
Henning Wackerhage, Kenneth A. Dyar, Martin Schönfelder
How is the oxygen concentration sensed? The ventilation-regulating signals of O2, CO2 and pH are sensed by peripheral chemoreceptors such as the carotid and aortic bodies and by central chemoreceptors in the brain. The ≈20 mm3 large carotid body, located at the bifurcation of the carotid artery that supplies the head and brain with oxygen, is a sensitive oxygen sensor that monitors the arterial O2 tension (PaO2) and stimulates ventilation when the PaO2 drops below ≈60 mmHg. The carotid body contains three main cell types (5, 6): Oxygen-sensing glomus cells (type 1),Subtentacular cells (type 2),Afferent nerve fibres whose axons convey the hypoxia message to the ventilation-regulating parts of the brain.
Diseases of the Aorta
Published in Mary N. Sheppard, Practical Cardiovascular Pathology, 2022
The normal aorta has a thin intima lined by endothelium with a few underlying elastic and collagen fibres, a prominent media containing parallel elastic lamellae separated by smooth-muscle cells, collagen fibres and a mucoid ground substance rich in proteoglycans and an adventitia consisting of fat, thick and thin-walled blood vessels with an outer layer of collagen with surface mesothelial cells (Fig. 8.1). There are often prominent lymphocytic aggregates around blood vessels in the adventitia which are not linked to medial inflammation which increase with age (Fig. 8.2). Aortic chemoreceptor tissue is distributed along the aorta, pulmonary arterial trunk, and subclavian arteries. These are commonly called ‘aortic’ bodies. Aortic bodies are sensory chemoreceptors and baroreceptors scattered throughout the aortic arch and its branches. Similar to the carotid body, aortic body chemoreceptors sense changes in Pao2, Paco2 and pH in the arterial blood. Signals from aortic body chemoreceptors travel via the vagus nerve to the medulla where respiratory centres are stimulated, increasing ventilatory drive. These can be seen scattered in the adventitia of the aorta with neuroendocrine cells positive for neuroendocrine markers and sustentacular cells positive for S-100, surrounded by ganglion cells and large nerve bundles (Figs. 8.3, 8.4). Be aware of their existence in resection specimens.
Control of Ventilation
Published in Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal, Principles of Physiology for the Anaesthetist, 2020
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal
The peripheral chemoreceptors are found in two locations. Carotid bodies, supplied by the glossopharyngeal nerve, lie at the bifurcation of the common carotid artery, and are more important in humans.Aortic bodies, supplied by the vagus nerve, lie in the aortic arch.
Novel approaches: targeting sympathetic outflow in the carotid sinus
Published in Blood Pressure, 2023
Dagmara Hering, Krzysztof Narkiewicz
The peripheral arterial chemoreceptors are located in the carotid and aortic bodies, and respond primarily to changes in oxygen levels (hypoxia), while central chemoreceptors are located on the ventral surface of the medulla oblongata and primarily respond to changes in carbon dioxide (CO2) levels (hypercapnia) [10,12]. Activation of afferent impulses from the carotid chemoreceptors in response to hypoxia leads to simultaneous activation of the cardiorespiratory centre in the medulla oblongata (synapsing to neurons in the caudal, commissural nucleus tractus solitarius, NTS) resulting in simultaneous hyperventilation and selective peripheral vasoconstriction (increased sympathetic activity to blood vessels). At the same time, hyperventilation through a stretch of thoracic afferents elicits an inhibitory or buffering influence on the autonomic response to hypoxaemia resulting in bradycardia, mediated by increased cardiac vagal outflow (Figure 2).
Dopamine β hydroxylase as a potential drug target to combat hypertension
Published in Expert Opinion on Investigational Drugs, 2020
Sanjay Kumar Dey, Manisha Saini, Pankaj Prabhakar, Suman Kundu
The arterial baro- and chemo-reflexes are negative feedback mechanisms to maintain the beat-to-beat homeostasis in ABP [21]. Sudden change in ABP is detected by baroreceptors in the circulatory walls of the carotid sinus and aortic arch. These afferent baroreceptors then induce a sympatho-inhibitory reflex, known as baroreflex from carotid sinus and aorta using glossopharyngeal and vagus nerves, respectively, toward NTS and normalizes BP by adjusting cardiac output and vascular resistance [22–24]. In case of chronic hypertension, baroreceptors loses sensitivity and remains unable to prevent sudden variation in BP [22–24]. On the other hand, chemoreflexes are induced by the chemoreceptors which sense the changes in arterial PO2, PCO2, and pH at their distinct vassal locations in the carotid bodies and aortic bodies [18,23]. Respiratory center in the brain is stimulated by chemoreflex due to decrease in PO2 and pH or increase in PCO2, which in turn induces the sympathetic outflow. In obstructive sleep apnea patients, repeated stimulation of chemoreflex by chronic hypoxia and hypercapnia increases the chance of hypertension [21,25].
Dyspnea in Parkinson’s disease: an approach to diagnosis and management
Published in Expert Review of Neurotherapeutics, 2020
Srimathy Vijayan, Bhajan Singh, Soumya Ghosh, Rick Stell, Frank L. Mastaglia
Dyspnea is a symptom commonly attributed to dysfunction of the respiratory or cardiovascular systems. From a respiratory perspective, a number of peripheral and central structures need to be considered. The former comprise the lung parenchyma and vasculature, upper airways, chest wall and respiratory musculature, while the central structures are the brainstem ventilatory control centers which are intricately linked to chemoreceptors in the carotid and aortic bodies. Pathological processes affecting any of these structures can result in dyspnea. However, it is likely that such a simplistic view may not be adequate. Thus the sensory component, resulting from neural activation of peripheral receptors, and the subjective perception of dyspnea are equally important [8,9]. Furthermore, the threshold at which an individual experiences dyspnea is variable [8]. These sensory components may be influenced by personality traits and cultural background of the individual. In addition, psychosocial aspects and environmental factors may further modulate behavioral practices. As such, dyspnea may be observed in a variety of social situations and perceived differently according to the individual state of mind at the time.