[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Physiology](https://durgical.com/en/physiology/) › [Respiratory](https://durgical.com/en/physiology/#s-resp) › Control of breathing, chemoreceptors and lung reflexes [Physiology](https://durgical.com/en/physiology/) · [Respiratory](https://durgical.com/en/physiology/#s-resp) # Control of breathing, chemoreceptors and lung reflexes - Regulation - Exam priority: high The brainstem sets the rhythm of breathing. Blood CO₂ tunes it most; low O₂ only matters once it falls a lot. Updated 2026-11-01 Also called: Respiratory centre, Central and peripheral chemoreceptors, Hering–Breuer reflex **See it in 3D:** [Medulla oblongata](https://durgical.com/en/anatomy/medulla-oblongata/) · [Pons](https://durgical.com/en/anatomy/pons/) · [Carotid bifurcation](https://durgical.com/en/anatomy/carotid-bifurcation/) · [Phrenic nerves](https://durgical.com/en/anatomy/phrenic-nerve/) · [Aortic arch](https://durgical.com/en/anatomy/aortic-arch/) · [Intercostal nerves](https://durgical.com/en/anatomy/intercostal-nerves/) ## Key points - CO₂ is the main minute-to-minute stimulus, acting on central chemoreceptors through CSF H⁺. - Peripheral chemoreceptors respond strongly once PaO₂ falls below ≈ 60 mmHg. - The carotid body (glossopharyngeal nerve) is the key O₂ sensor; aortic bodies signal via the vagus. - Dorsal respiratory group: inspiration; ventral group: forced expiration and active breathing; pons: inspiratory timing. - Opioids blunt the CO₂ response and the rate; naloxone reverses it. - In chronic hypercapnia CSF is compensated with bicarbonate and hypoxemia gains weight as a stimulus. ## What it is Groups of neurons in the medulla generate the breathing rhythm and the pons fine-tunes it. Central chemoreceptors sense the H⁺ that CO₂ produces in cerebrospinal fluid; peripheral chemoreceptors (carotid and aortic bodies) sense mainly low PaO₂, plus CO₂ and H⁺. Lung receptors and the cortex adjust the pattern. ## How it works, step by step - Arterial CO₂ crosses the blood–brain barrier easily; H⁺ and HCO₃⁻ cross poorly. - In CSF, CO₂ forms H⁺, which stimulates chemoreceptors on the ventral surface of the medulla. - The respiratory centre raises rate and depth, alveolar ventilation rises and PaCO₂ falls. - If PaO₂ falls below ≈ 60 mmHg, the carotid body fires and adds a strong ventilatory drive. - As the lung distends, stretch receptors signal via the vagus and cut inspiration short (Hering–Breuer). - Over days at altitude the kidney excretes bicarbonate, pH normalises and ventilation can stay high (acclimatization). ## Regulation - *+* **High PaCO₂ / low CSF pH**: Strongly increases ventilation (central chemoreceptors). - *+* **PaO₂ | Sensor | Where | What it senses | | --- | --- | --- | | Central chemoreceptors | Ventral surface of the medulla | CSF H⁺ (reflects PaCO₂) | | Carotid bodies | Carotid bifurcation (CN IX) | Low PaO₂, high PaCO₂, high H⁺ | | Aortic bodies | Aortic arch (CN X) | Low PaO₂, high PaCO₂ | | Stretch receptors | Airway smooth muscle (CN X) | Lung distension | ## Clinical notes - Opioid overdose: bradypnea, pinpoint pupils, hypercapnia; naloxone restores breathing. - COPD with chronic CO₂ retention: excessive supplemental O₂ can push PaCO₂ higher (V/Q, Haldane and less hypoxic drive). - Obstructive sleep apnea: the airway collapses while breathing effort continues; rising CO₂ wakes the patient. - Arriving in Bogotá from the coast: hyperventilation and mild respiratory alkalosis in the first days. ## Memory aid CO₂ is the 'minute-by-minute boss'; low O₂ is the 'emergency alarm' that goes off below 60. ## Test yourself Think of the answer, then tap the question to see it. ## Why do central chemoreceptors respond to CO₂ rather than to blood H⁺? CO₂ crosses the blood–brain barrier and forms H⁺ in CSF; blood H⁺ and bicarbonate cross very poorly. ## Which chemoreceptors explain Kussmaul breathing in ketoacidosis? The peripheral ones, mainly the carotid bodies, which sense arterial H⁺; central receptors respond later. ## Why is the initial hyperventilation at altitude held back in the first hours? Falling PaCO₂ raises CSF pH, which brakes the central chemoreceptors; over days CSF and plasma bicarbonate fall and ventilation keeps rising. ## Which nerve carries carotid body signals to the brainstem? The glossopharyngeal nerve (CN IX), through its carotid sinus branch. ## What does morphine do to the ventilatory response curve to CO₂? It flattens it and shifts it right: more CO₂ is needed for the same ventilation. [Add to my cards (5)](https://durgical.app/estudiar/?add=/en/physiology/control-of-breathing-chemoreceptors-and-lung-reflexes/) ## See it in 3D The structures of Durgical's 3D anatomy where it happens. - [Medulla oblongata](https://durgical.com/en/anatomy/medulla-oblongata/) - [Pons](https://durgical.com/en/anatomy/pons/) - [Carotid bifurcation](https://durgical.com/en/anatomy/carotid-bifurcation/) - [Phrenic nerves](https://durgical.com/en/anatomy/phrenic-nerve/) - [Aortic arch](https://durgical.com/en/anatomy/aortic-arch/) - [Intercostal nerves](https://durgical.com/en/anatomy/intercostal-nerves/) ## Related topics - [Abnormal breathing patterns and sleep apnea](https://durgical.com/en/physiology/abnormal-breathing-patterns-and-sleep-apnea/) - [High altitude and acclimatization](https://durgical.com/en/physiology/high-altitude-and-acclimatization/) - [CO₂ transport and the Haldane effect](https://durgical.com/en/physiology/co-transport-and-the-haldane-effect/) - [Respiratory acidosis and alkalosis](https://durgical.com/en/physiology/respiratory-acidosis-and-alkalosis/) - [Mechanics of breathing: pressures and muscles](https://durgical.com/en/physiology/mechanics-of-breathing-pressures-and-muscles/) ## Related conditions - [Chronic obstructive pulmonary disease (COPD)](https://durgical.com/en/conditions/chronic-obstructive-pulmonary-disease/) - [Obstructive sleep apnoea](https://durgical.com/en/conditions/obstructive-sleep-apnoea/) - [Respiratory alkalosis](https://durgical.com/en/conditions/respiratory-alkalosis/) - [Respiratory acidosis](https://durgical.com/en/conditions/respiratory-acidosis/) - [Diabetic ketoacidosis](https://durgical.com/en/conditions/diabetic-ketoacidosis/) ## In Pharmacology - [Opioids and antagonists](https://durgical.com/en/pharmacology/classes/opioids-and-antagonists/) - [Morphine](https://durgical.com/en/pharmacology/morphine/) - [Naloxone](https://durgical.com/en/pharmacology/naloxone/) [← All of physiology](https://durgical.com/en/physiology/) Educational physiology content; not a diagnostic or treatment guide and no substitute for a health professional's advice. Values are approximate references. No doses are given. Sources: [22.3 The Process of Breathing](https://openstax.org/books/anatomy-and-physiology-2e/pages/22-3-the-process-of-breathing) (OpenStax (Rice University), 2022); [Neuroanatomy, Medulla Oblongata](https://www.ncbi.nlm.nih.gov/books/NBK551589/) (StatPearls (NCBI Bookshelf), 2024); [Obstructive Sleep Apnea](https://www.ncbi.nlm.nih.gov/books/NBK459252/) (StatPearls (NCBI Bookshelf), 2024); Hall JE. Guyton and Hall Textbook of Medical Physiology, 13th ed. (ch. 42). Reference book used to check facts; its text and figures are not reproduced (Elsevier, 2016). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/physiology/control-of-breathing-chemoreceptors-and-lung-reflexes/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/physiology/control-of-breathing-chemoreceptors-and-lung-reflexes/