[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Physiology](https://durgical.com/en/physiology/) › [Cardiovascular](https://durgical.com/en/physiology/#s-cardio) › The baroreceptor reflex [Physiology](https://durgical.com/en/physiology/) · [Cardiovascular](https://durgical.com/en/physiology/#s-cardio) # The baroreceptor reflex - Regulation - Exam priority: high Pressure sensors in the neck and aorta tell the brain about blood pressure each second, and the brain adjusts heart and vessels to keep it steady. Updated 2026-11-01 Also called: Arterial baroreflex, Carotid sinus reflex **See it in 3D:** [Carotid bifurcation](https://durgical.com/en/anatomy/carotid-bifurcation/) · [Aortic arch](https://durgical.com/en/anatomy/aortic-arch/) · [Glossopharyngeal nerve (IX)](https://durgical.com/en/anatomy/glossopharyngeal-nerve/) · [Vagus nerve](https://durgical.com/en/anatomy/vagus-nerve/) · [Medulla oblongata](https://durgical.com/en/anatomy/medulla-oblongata/) ## Key points - Carotid sinus → glossopharyngeal nerve (IX); aortic arch → vagus nerve (X); both to the nucleus tractus solitarius in the medulla. - ↑ Pressure → ↑ firing → ↑ vagal, ↓ sympathetic → ↓ HR, ↓ contractility, ↓ SVR, ↓ venous tone. - Most sensitive around normal mean pressure (≈ 90–100 mmHg); works over ≈ 60–180 mmHg; carotid receptors respond more to change than to a steady level. - Resets toward the new pressure within 1–2 days, so it is a short-term buffer, not a long-term controller. - Carotid sinus massage or the Valsalva release slow the heart via the vagus: used to stop some supraventricular tachycardias. ## What it is Stretch receptors in the carotid sinus and aortic arch fire faster when arterial pressure rises. The medulla responds by increasing vagal output and reducing sympathetic output, which lowers heart rate, contractility and vascular resistance. The reflex buffers moment-to-moment changes (standing up, bleeding) but resets within days, so it does not set long-term pressure. ## Key facts - Cardiopulmonary (low-pressure) receptors in the atria and pulmonary veins sense volume and adjust ADH, ANP and renal sympathetic tone. - Peripheral chemoreceptors (carotid and aortic bodies) respond to low O₂, high CO₂ or low pH and raise pressure when it is very low. - Denervating the baroreceptors makes pressure much more variable but leaves the long-term average almost unchanged. ## How it works, step by step - Arterial pressure rises and stretches the walls of the carotid sinus and aortic arch. - Mechanosensitive endings fire more action potentials. - Signals travel in IX (carotid) and X (aortic) to the nucleus tractus solitarius. - The NTS stimulates the vagal nuclei and inhibits the vasomotor centre (rostral ventrolateral medulla). - Heart rate and contractility fall; arterioles and veins dilate. - Cardiac output and resistance fall, bringing pressure back toward its set point. - A fall in pressure does the opposite: tachycardia, vasoconstriction and venoconstriction within seconds. ## Regulation - *−* **High arterial pressure (more baroreceptor firing)**: Vagal activation and sympathetic withdrawal: lower HR, SVR and pressure. - *+* **Low arterial pressure (less firing)**: Sympathetic activation: tachycardia, vasoconstriction, more renin. - *−* **Carotid sinus massage**: Strong vagal slowing of the SA and AV nodes. ## Clinical notes - Orthostatic hypotension appears when the reflex fails: autonomic neuropathy (diabetes, Parkinson disease), volume loss, or some drugs. - Carotid sinus hypersensitivity can cause syncope when turning the head or wearing a tight collar. ## Memory aid The baroreceptors are a thermostat for pressure: too high, open the windows (vagus on, sympathetic off); too low, turn on the heater. ## Test yourself Think of the answer, then tap the question to see it. ## A patient loses 1 L of blood quickly. What does the baroreceptor reflex do in the first seconds? Lower pressure reduces baroreceptor firing, so vagal tone falls and sympathetic output rises: tachycardia, more contractility, arteriolar and venous constriction. ## Why is the baroreceptor reflex not effective in controlling long-term blood pressure? The receptors reset to the prevailing pressure within a day or two, so a sustained change stops producing a corrective signal; long-term control is renal. ## Which cranial nerves carry the carotid sinus and aortic arch signals? The glossopharyngeal nerve (IX) from the carotid sinus and the vagus nerve (X) from the aortic arch, both to the nucleus tractus solitarius. ## Why does a drug that causes strong arteriolar vasodilation often produce tachycardia? The fall in pressure unloads the baroreceptors, which triggers sympathetic activation and reflex tachycardia. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/physiology/the-baroreceptor-reflex/) ## See it in 3D The structures of Durgical's 3D anatomy where it happens. - [Carotid bifurcation](https://durgical.com/en/anatomy/carotid-bifurcation/) - [Aortic arch](https://durgical.com/en/anatomy/aortic-arch/) - [Glossopharyngeal nerve (IX)](https://durgical.com/en/anatomy/glossopharyngeal-nerve/) - [Vagus nerve](https://durgical.com/en/anatomy/vagus-nerve/) - [Medulla oblongata](https://durgical.com/en/anatomy/medulla-oblongata/) ## Related topics - [Nervous control of the circulation and the CNS ischemic response](https://durgical.com/en/physiology/nervous-control-of-the-circulation-and-the-cns-ischemic-response/) - [The response to standing up](https://durgical.com/en/physiology/the-response-to-standing-up/) - [Long-term blood pressure control by the kidney](https://durgical.com/en/physiology/long-term-blood-pressure-control-by-the-kidney/) - [Shock physiology](https://durgical.com/en/physiology/shock-physiology/) - [Systolic, diastolic, mean and pulse pressure](https://durgical.com/en/physiology/systolic-diastolic-mean-and-pulse-pressure/) ## Related conditions - [Hypovolaemic shock](https://durgical.com/en/conditions/hypovolaemic-shock/) - [Arterial hypertension](https://durgical.com/en/conditions/arterial-hypertension/) ## In Pharmacology - [Beta blockers](https://durgical.com/en/pharmacology/classes/beta-blockers/) [← 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: [20.4 Homeostatic Regulation of the Vascular System](https://openstax.org/books/anatomy-and-physiology-2e/pages/20-4-homeostatic-regulation-of-the-vascular-system) (OpenStax (Rice University), 2022); [19.4 Cardiac Physiology](https://openstax.org/books/anatomy-and-physiology-2e/pages/19-4-cardiac-physiology) (OpenStax (Rice University), 2022); Hall JE. Guyton and Hall Textbook of Medical Physiology, 13th ed. (ch. 18). 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/the-baroreceptor-reflex/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/physiology/the-baroreceptor-reflex/