Information about Baroreceptor Reflex
In cardiovascular physiology, the baroreflex or baroreceptor reflex is one of the body's homeostatic mechanisms for maintaining blood pressure. It provides a negative feedback loop in which an elevated blood pressure reflexively causes blood pressure to decrease; similarly, decreased blood pressure depresses the baroreflex, causing blood pressure to rise.
The system relies on specialized neurons (baroreceptors) in the aortic arch, carotid sinuses, and elsewhere to monitor changes in blood pressure and relay them to the brainstem. Subsequent changes in blood pressure are mediated by the autonomic nervous system.
The NTS sends excitatory fibers (glutamatergic) to the caudal ventrolateral medulla (CVLM), thus activating the CVLM. The activated CVLM then sends inhibitory fibers (GABAergic) to the rostral ventrolateral medulla (RVLM), thus inhibiting the RVLM. The RVLM is the primary regulator of sympathetic nervous system, sending excitatory fibers (catecholaminergic) to the sympathetic preganglionic neurons in the spinal cord. Hence, when the baroreceptors are activated (by an increased blood pressure), the NTS activates the CVLM, which in turn inhibits the RVLM, thus inhibiting the sympathetic branch of the autonomic nervous system leading to a decrease in blood pressure. Likewise, low blood pressure causes an increase in sympathetic tone via "disinhibition" (less inhibition, hence activation) of the RVLM.
The NTS also sends excitatory fibers to the vagal nuclei that regulate the parasympathetic nervous system, aiding in the decrease in sympathetic activity during conditions of elevated blood pressure.
These action potentials are relayed to the nucleus of the tractus solitarius (NTS), which uses frequency as a measure of blood pressure. As discussed previously, increased activation of the NTS inhibits the vasomotor center and stimulates the vagal nuclei. The end result of baroreceptor activation is inhibition of the sympathetic nervous system and activation of the parasympathetic nervous system.
The sympathetic and parasympathetic branches of the autonomic nervous system have opposing effects on blood pressure. Sympathetic activation leads to an elevation of total peripheral resistance and cardiac output via increased contractility of the heart, heart rate, and arterial vasoconstriction, which tends to increase blood pressure. Conversely, parasympathetic activation leads to a decreased cardiac output via decrease in contractility and heart rate, resulting in a tendency to decrease blood pressure.
By coupling sympathetic inhibition and parasympathetic activation, the baroreflex maximizes blood pressure reduction. Sympathetic inhibition leads to a drop in peripheral resistance, while parasympathetic activation leads to a depressed heart rate and contractility. The combined effects will dramatically decrease blood pressure.
Similarly, sympathetic activation with parasympathetic inhibition allows the baroreflex to elevate blood pressure.
CVRx, Inc., a private company located in Minneapolis, Minnesota, has developed an implantable device to treat patients with high blood pressure that cannot be controlled with medications (resistant hypertension) by electrically activating the baroreceptors. This investigational device is called the Rheos® Baroreflex Hypertension Therapy™ System. It is currently under evaluation in an FDA-regulated, phase III clinical trial: the Rheos Pivotal Trial.
At a MAP below approximately 50 mm Hg, baroreceptors are completely silent.
The system relies on specialized neurons (baroreceptors) in the aortic arch, carotid sinuses, and elsewhere to monitor changes in blood pressure and relay them to the brainstem. Subsequent changes in blood pressure are mediated by the autonomic nervous system.
Anatomy of the reflex
Baroreceptors include those in the auricles of the heart and vena cavae, but the most sensitive baroreceptors are in the carotid sinuses and aortic arch. The carotid sinus baroreceptors are innervated by the glossopharyngeal nerve (CN IX); the aortic arch baroreceptors are innervated by the vagus nerve (CN X). Baroreceptor activity travels along these nerves, which contact the nucleus of the solitary tract (NTS) in the brainstem.The NTS sends excitatory fibers (glutamatergic) to the caudal ventrolateral medulla (CVLM), thus activating the CVLM. The activated CVLM then sends inhibitory fibers (GABAergic) to the rostral ventrolateral medulla (RVLM), thus inhibiting the RVLM. The RVLM is the primary regulator of sympathetic nervous system, sending excitatory fibers (catecholaminergic) to the sympathetic preganglionic neurons in the spinal cord. Hence, when the baroreceptors are activated (by an increased blood pressure), the NTS activates the CVLM, which in turn inhibits the RVLM, thus inhibiting the sympathetic branch of the autonomic nervous system leading to a decrease in blood pressure. Likewise, low blood pressure causes an increase in sympathetic tone via "disinhibition" (less inhibition, hence activation) of the RVLM.
The NTS also sends excitatory fibers to the vagal nuclei that regulate the parasympathetic nervous system, aiding in the decrease in sympathetic activity during conditions of elevated blood pressure.
Baroreceptor activation
The baroreceptors are stretch-sensitive mechanoreceptors. When blood pressure rises, the carotid and aortic sinuses are distended, resulting in stretch and therefore activation of the baroreceptors. Active baroreceptors fire action potentials ("spikes") more frequently than inactive baroreceptors. The greater the stretch, the more rapidly baroreceptors fire action potentials.These action potentials are relayed to the nucleus of the tractus solitarius (NTS), which uses frequency as a measure of blood pressure. As discussed previously, increased activation of the NTS inhibits the vasomotor center and stimulates the vagal nuclei. The end result of baroreceptor activation is inhibition of the sympathetic nervous system and activation of the parasympathetic nervous system.
The sympathetic and parasympathetic branches of the autonomic nervous system have opposing effects on blood pressure. Sympathetic activation leads to an elevation of total peripheral resistance and cardiac output via increased contractility of the heart, heart rate, and arterial vasoconstriction, which tends to increase blood pressure. Conversely, parasympathetic activation leads to a decreased cardiac output via decrease in contractility and heart rate, resulting in a tendency to decrease blood pressure.
By coupling sympathetic inhibition and parasympathetic activation, the baroreflex maximizes blood pressure reduction. Sympathetic inhibition leads to a drop in peripheral resistance, while parasympathetic activation leads to a depressed heart rate and contractility. The combined effects will dramatically decrease blood pressure.
Similarly, sympathetic activation with parasympathetic inhibition allows the baroreflex to elevate blood pressure.
CVRx, Inc., a private company located in Minneapolis, Minnesota, has developed an implantable device to treat patients with high blood pressure that cannot be controlled with medications (resistant hypertension) by electrically activating the baroreceptors. This investigational device is called the Rheos® Baroreflex Hypertension Therapy™ System. It is currently under evaluation in an FDA-regulated, phase III clinical trial: the Rheos Pivotal Trial.
Set point and tonic activation
Baroreceptors are active above the baroreceptor set point at mean arterial pressures (MAP) above approximately 70 mm Hg. When MAP falls below the set point, baroreceptors are almost silent. The baroreceptor set point is not fixed; its value may change with changes in blood pressure. For example, in hypertension, the set point will increase; on the other hand, hypotension will result in a depression of the baroreceptor set point.At a MAP below approximately 50 mm Hg, baroreceptors are completely silent.
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 [Sleight, 1995].See also
References
- Berne, Robert M., Levy, Matthew N. (2001). Cardiovascular Physiology. Philadelphia, PA: Mosby.
- Boron, Walter F., Boulpaep, Emile L. (2005). Medical Physiology: A Cellular and Molecular Approach. Philadelphia, PA: Elsevier/Saunders.
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id="CITEREFSleight1995">Sleight, P. (1995), "Physiology and pathophysiology of heart rate and blood pressure variability in humans. Is power spectral analysis largely an index of baroreflex gain?", Clinical Science, 88: 103-109
Cardiovascular physiology is the study of the circulatory system. More specifically, it addresses the physiology of the heart ("cardio") and blood vessels ("vascular").
..... Click the link for more information.Homeostasis is the property of either an open system or a closed system, especially a living organism, to regulate the state of its internal environment so as to maintain a stable, constant condition.
..... Click the link for more information.Blood pressure (strictly speaking: vascular pressure) refers to the force exerted by circulating blood on the walls of blood vessels, and constitutes one of the principal vital signs.
..... Click the link for more information.Negative feedback feeds part of a system's output, inverted, into the system's input; generally with the result that fluctuations are attenuated. Many real-world systems have one or several points around which the system gravitates.
..... Click the link for more information.Neurons (also known as neurones and nerve cells) are electrically excitable cells in the nervous system that process and transmit information. In vertebrate animals, neurons are the core components of the brain, spinal cord and peripheral nerves.
..... Click the link for more information.Baroreceptors (or baroceptors) in the human body detect the pressure of blood flowing through them, and can send messages to the central nervous system to increase or decrease total peripheral resistance and cardiac output.
..... Click the link for more information.- For the embryological structure, see Aortic arches.
The arch of the aorta (Transverse Aorta) begins at the level of the upper border of the second sternocostal articulation of the right side, and runs at first upward, backward, and to the left in
..... Click the link for more information.In human anatomy, the carotid sinus is a localized dilation of the internal carotid artery at its origin, the common carotid artery bifurcation.Functions
It contains numerous baroreceptors, which function as a "sampling area" for many homeostatic mechanisms for
..... Click the link for more information.The brain stem is the lower part of the brain, adjoining and structurally continuous with the spinal cord. Most sources consider the pons, medulla oblongata, and midbrain all to be part of the brainstem.
..... Click the link for more information.autonomic nervous system (ANS) (or visceral nervous system) is the part of the peripheral nervous system that acts as a control system, maintaining homeostasis in the body. These maintenance activities are primarily performed without conscious control or sensation.
..... Click the link for more information.heart is a muscular organ responsible for pumping blood through the blood vessels by repeated, rhythmic contractions, or a similar structure in the annelids, mollusks, and arthropods.
..... Click the link for more information.The superior and inferior vena cava are collectively called the venae cavae. They are the veins that return de-oxygenated blood from the body into the heart. They both empty into the right atrium.
..... Click the link for more information.The glossopharyngeal nerve is the ninth of twelve pairs of cranial nerves. It exits the brainstem out from the sides of the upper medulla, just rostral (closer to the nose) to the vagus nerve.
..... Click the link for more information.The vagus nerve (also called pneumogastric nerve or cranial nerve X) is the tenth of twelve paired cranial nerves, and is the only nerve that starts in the brainstem (within the medulla oblongata) and extends, through the jugular foramen, down below the head, to the
..... Click the link for more information.The solitary nucleus and tract are structures in the brainstem that carry and receive visceral sensation and taste from the facial (VII), glossopharyngeal (IX), vagus (X) cranial nerves, as well as the cranial part of the accessory nerve (XI).
..... Click the link for more information.Stretching, as theorized in literature, is the deliberate act of lengthening of muscles, in order to increase muscle flexibility and/or joint range of motion (Weerapong et al 189-206).
..... Click the link for more information.A mechanoreceptor is a sensory receptor that responds to mechanical pressure or distortion. There are four main types in the glabrous skin of humans: Pacinian corpuscles, Meissner's corpuscles, Merkel's discs, and Ruffini corpuscles.
..... Click the link for more information.An action potential is a "spike" of electrical discharge that travels along the membrane of a cell. Action potentials are an essential feature of animal life, rapidly carrying information within and between tissues. They also occur in some plants.
..... Click the link for more information.The solitary nucleus and tract are structures in the brainstem that carry and receive visceral sensation and taste from the facial (VII), glossopharyngeal (IX), vagus (X) cranial nerves, as well as the cranial part of the accessory nerve (XI).
..... Click the link for more information.The Sympathetic Nervous System (SNS) is a branch of the autonomic nervous system. It is always active at a basal level (called sympathetic tone) and becomes more active during times of stress.
..... Click the link for more information.parasympathetic nervous system (PSNS) is one of three divisions of the autonomic nervous system (ANS). The ANS -a subdivision of the peripheral nervous system (PNS)- is subdivided into the sympathetic (SNS), parasympathetic (PSNS) and enteric (bowels) nervous system (ENS).
..... Click the link for more information.autonomic nervous system (ANS) (or visceral nervous system) is the part of the peripheral nervous system that acts as a control system, maintaining homeostasis in the body. These maintenance activities are primarily performed without conscious control or sensation.
..... Click the link for more information.Total peripheral resistance refers to the cumulative resistance of the thousands of arterioles in the body, or the lungs, respectively. It is approximately equal to the resistance of the arterioles, since the arterioles are the chief resistance vessels in the body.
..... Click the link for more information.Cardiac output (CO) is the volume of blood being pumped by the heart, in particular by a ventricle in a minute.Normal Output
Cardiac output is equal to the stroke volume (SV) multiplied by the heart rate (HR).
..... Click the link for more information.Myocardial Contractility is a term used in physiology to describe the performance of cardiac muscle.
It is often defined as: the intrinsic ability of a cardiac muscle fibre to contract at a given fibre length.
..... Click the link for more information.Heart rate is a term used to describe the frequency of the cardiac cycle. It is considered one of the four vital signs. Usually it is calculated as the number of contractions (heart beats) of the heart in one minute and expressed as "beats per minute" (bpm).
..... Click the link for more information.Vasoconstriction is a narrowing of the lumen of blood vessels.Factors
Factors that trigger vasoconstriction are both of exogenous origin, i.e. medication, and as a response from the body itself.Body mechanisms
Vasoconstriction is a procedure of the body to e.g.
..... Click the link for more information.Set point might mean one of:- Set point (tennis), a tennis term meaning one player is one point away from winning a set
- Set point (electronics), a term which refers to the point at which an electrical circuit is either activated or de-activated
..... Click the link for more information.The mean arterial pressure (MAP) is a term used in medicine to describe a notional average blood pressure in an individual. It is defined as the average arterial pressure during a single cardiac cycle.
..... Click the link for more information.Hypertension
Classification & external resources
ICD-10 I 10. ,I 11. ,I 12. ,
I 13. ,I 15.
ICD-9 401.x
OMIM 145500
DiseasesDB 6330
MedlinePlus 000468
eMedicine med/1106 ped/1097 emerg/267
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