Baroreflex
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The baroreflex or baroreceptor reflex is one of the body's
The system relies on specialized neurons, known as baroreceptors, chiefly in the aortic arch and carotid sinuses, to monitor changes in blood pressure and relay them to the medulla oblongata. Baroreceptors are stretch receptors and respond to the pressure induced stretching of the blood vessel in which they are found. Baroreflex-induced changes in blood pressure are mediated by both branches of the autonomic nervous system: the parasympathetic and sympathetic nerves. Baroreceptors are active even at normal blood pressures so their activity informs the brain about both increases and decreases in blood pressure.
The body contains two other, slower-acting systems to regulate blood pressure: the heart releases atrial natriuretic peptide when blood pressure is too high, and the kidneys sense and correct low blood pressure with the renin–angiotensin system.[2]
Anatomy
Baroreceptors are present in the
The SN neurons send excitatory fibers (
Even at resting levels of blood pressure, arterial baroreceptor discharge activates SN neurons. Some of these SN neurons are tonically activated by this resting blood pressure and thus activate excitatory fibers to the nucleus ambiguus and dorsal nucleus of vagus nerve to regulate the parasympathetic nervous system. These parasympathetic neurons send axons to the heart and parasympathetic activity slows cardiac pacemaking and thus heart rate. This parasympathetic activity is further increased during conditions of elevated blood pressure. The parasympathetic nervous system is primarily directed toward the heart.[citation needed]
Activation
The
Baroreceptor mechanosensitivity is hypothesised to be linked to the expression of PIEZO1 and PIEZO2 on neurons in the petrosal and nodose ganglia.
Baroreceptor action potentials are relayed to the
The
By coupling
Set point and tonic activation
Baroreceptor firing has an inhibitory effect on sympathetic outflow. The sympathetic neurons fire at different rates which determines the release of norepinephrine onto cardiovascular targets. Norepinephrine constricts blood vessels to increase blood pressure. When baroreceptors are stretched (due to an increased blood pressure) their firing rate increases which in turn decreases the sympathetic outflow resulting in reduced norepinephrine and thus blood pressure. When the blood pressure is low, baroreceptor firing is reduced and this in turn results in augmented sympathetic outflow and increased norepinephrine release on the heart and blood vessels, increasing blood pressure.[citation needed]
Effect on heart rate variability
The baroreflex may be responsible for a part of the low-frequency component of heart rate variability, the so-called Mayer waves, at 0.1 Hz.[4]
Baroreflex activation therapy
High blood pressure
The baroreflex can be used to treat resistant hypertension.[5] This stimulation is provided by a pacemaker-like device. While the devices appears to lower blood pressure, evidence remains very limited as of 2018.[5]
Heart failure
The ability of baroreflex activation therapy to reduce sympathetic nerve activity suggests a potential in the treatment of chronic heart failure, because in this condition there is often intense sympathetic activation and patients with such sympathetic activation show a markedly increased risk of fatal arrhythmias and death.[citation needed]
One trial[6] has already shown that baroreflex activation therapy improves functional status, quality of life, exercise capacity and N-terminal pro-brain natriuretic peptide.[citation needed]
See also
References
- PMID 26157417.
- PMID 29344085.
They are mainly produced by cardiovascular, brain and renal tissues in response to wall stretch and other causes. NPs provide natriuresis, diuresis, vasodilation, antiproliferation, antihypertrophy, antifibrosis and other cardiometabolic protection. NPs represent body's own antihypertensive system, and provide compensatory protection to counterbalance vasoconstrictor-mitogenic-sodium retaining hormones, released by renin-angiotensin-aldosterone system (RAAS) and sympathetic nervous system (SNS).
- ISBN 978-1-26-012240-4.
- PMID 7677832.
- ^ PMID 29136223.
- PMID 25982108.
- Boron, Walter F.; Boulpaep, Emile L. (2005). Medical Physiology: A Cellular and Molecular Approach. Philadelphia, PA: Elsevier/Saunders. ISBN 1-4160-2328-3.
- Sleight, P.; M.T. La Rovere; A. Mortara; G. Pinna; R. Maestri; S. Leuzzi; B. Bianchini; L. Tavazzi; L. Bernardi (1995). "Physiology and pathophysiology of PMID 7677832.
- Heesch, C. (1999). "Reflexes that control cardiovascular function". American Journal of Physiology. 277 (6 Pt 2): S234–S243. S2CID 21912789.