baroreceptor reflex
Summary
The baroreceptor reflex is a rapid, negative feedback mechanism that maintains blood pressure homeostasis by detecting changes in arterial pressure and adjusting heart rate and vascular tone accordingly. Increased BP → decreased HR and vasodilation; decreased BP → increased HR and vasoconstriction.
Detail
The baroreceptor reflex involves specialized mechanoreceptors located in the carotid sinus and aortic arch that detect stretch caused by changes in blood pressure. When BP increases, baroreceptors fire more frequently, sending signals via the glossopharyngeal (CN IX) and vagus (CN X) nerves to the medullary cardiovascular control center. This activates the parasympathetic nervous system and inhibits sympathetic outflow, resulting in decreased heart rate (negative chronotropy), decreased contractility (negative inotropy), and vasodilation. Conversely, when BP decreases, reduced baroreceptor firing leads to sympathetic activation and parasympathetic withdrawal, causing increased heart rate, increased contractility, and vasoconstriction. This reflex operates within seconds and is crucial for maintaining cerebral and coronary perfusion during postural changes. Baroreceptor sensitivity can be impaired in conditions like diabetes, aging, and hypertension, leading to orthostatic hypotension and reduced heart rate variability.
Sources
- Guyton and Hall Textbook of Medical Physiology
- Boron and Boulpaep Medical Physiology
- Ganong's Review of Medical Physiology
- First Aid for the USMLE Step 1
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