Rapid Review·Cardiovascular
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PHYSIOLOGY
T2High yieldCardiovascular Reflexes: ANP, BNP, Baroreceptors & Chemoreceptors
FA P298
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Focus on
The heart’s own diuretic hormones, and the reflex arcs that defend blood pressure.
Key takeaways
The heart's own diuretic hormones
ANP
released from atrial myocytes when blood volume and atrial pressure rise. Acts through cGMP.- Causes vasodilation and reduced Na+ reabsorption at the renal collecting tubule.
- Dilates the afferent arteriole and constricts the efferent arteriole, promoting diuresis, and contributes to "aldosterone escape."
BNP
released from ventricular myocytes in response to increased wall tension. Same actions as ANP with a longer half-life.- Used to diagnose heart failure, where its value is the excellent negative predictive value: a normal BNP effectively excludes it.
| Feature | ANP | BNP |
|---|---|---|
| Source | Atrial myocytes | Ventricular myocytes |
| Trigger | Raised blood volume and atrial pressure | Raised ventricular wall tension |
| Half-life | Shorter | Longer |
| Clinical use | "Aldosterone escape" | Diagnosing heart failure, excellent negative predictive value |
| Renal arterioles | Dilates afferent, constricts efferent, causing diuresis | Same |
Baroreceptors
The receptors and their nerves
traced on the baroreceptor and chemoreceptor reflex diagram: aortic arch via CN X (vagus) and carotid sinus via CN IX (glossopharyngeal), both terminating in the nucleus tractus solitarius of the medulla.The hypotension response
the compensatory chain in hypovolemic shock: arterial pressure falls, stretch falls, afferent baroreceptor firing falls, so sympathetic outflow rises and parasympathetic falls, producing vasoconstriction, tachycardia, and increased contractility.Carotid sinus hypersensitivity
triggered by carotid massage, shaving, or a tight necktie. Rising carotid sinus pressure raises afferent firing, lengthens the AV node refractory period, slows the heart, and drops cardiac output, causing presyncope or syncope.| Receptor | Cranial nerve |
|---|---|
| Aortic arch | CN X (vagus) |
| Carotid sinus | CN IX (glossopharyngeal) |
Chemoreceptors, and the one that ignores oxygen
Peripheral (carotid and aortic bodies)
stimulated by raised PCO2, low pH, and low PO2 below 60 mm Hg.Central (medulla)
stimulated by low pH and raised PCO2 of brain interstitial fluid, and do NOT respond to PO2 at all, because H+ cannot cross the blood-brain barrier. They become less sensitive when PCO2 is chronically high, as in COPD, which shifts the drive onto the peripheral receptors.| Feature | Peripheral (carotid and aortic bodies) | Central (medulla) |
|---|---|---|
| Responds to raised PCO2 | Yes | Yes |
| Responds to low pH | Yes (blood) | Yes (brain interstitial fluid) |
| Responds to low PO2 | Yes, below 60 mm Hg | NO |
| In chronic COPD | Becomes the dominant drive | Less sensitive to chronically raised PCO2 |
Why does a patient with COPD who chronically retains CO2 come to depend on hypoxic drive?
The central chemoreceptors grow less sensitive to the chronically raised PCO2 and never respond to PO2, so the peripheral receptors, firing when PO2 falls below 60 mm Hg, take over.
How it's tested
Central chemoreceptors do not respond to oxygen at all, only to CO2 and pH, because H+ cannot cross the blood-brain barrier. That is why a COPD patient who chronically retains CO2 becomes dependent on the peripheral chemoreceptors and their hypoxic drive. The Cushing reflex triad of hypertension, bradycardia, and respiratory depression signals raised intracranial pressure, and the point they usually test is that the bradycardia is a baroreceptor response to the hypertension, not a primary event.
Go deeper
First Aid 2026 — CV/Physiology (p.298) · B&B — Baroreceptor reflex · Mehlman — HY Cardio (BNP, Cushing reflex), HY Pulmonary (hypoxic drive)
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Flashcards for this page
Card 1 of 5 · try-out only, nothing is saved
Activation of atrial natriuretic peptide → (...)-mediated (...) of the afferent arteriole and (...) of the efferent arteriole → Promotes diuresis and counteracts the effects of aldosterone
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