Baroreceptor
Encyclopedia
Baroreceptors are sensors located in the blood vessels of several mammals. They are a type of mechanoreceptor
that detects 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
. Baroreceptors act immediately as part of a negative feedback
system called the baroreflex
, as soon as there is a change from the usual mean arterial blood pressure
, returning the pressure to a normal level. They are an example of a short-term blood pressure regulation mechanism. Baroreceptors detect the amount of stretch of the blood vessel walls, and send the signal to the nervous system in response to this stretch. The nucleus tractus solitarius in the medulla oblongata
recognizes changes in the firing rate of action potential
s from the baroreceptors, and influences cardiac output and systemic vascular resistance through changes in the autonomic nervous system
.
Baroreceptors can be divided into two categories: high-pressure arterial baroreceptors and low-pressure baroreceptors (also known as cardiopulmonary or volume receptors).
es of the left and right internal carotid arteries. The baroreceptors found within the aortic arch monitor the pressure of blood delivered to the systemic circuit, and the baroreceptors within the carotid arteries monitor the pressure of the blood being delivered to the brain.
Arterial baroreceptors are stretch receptors that are stimulated by distortion of the arterial wall when pressure changes. The baroreceptors can identify the changes in both the average blood pressure or the rate of change in pressure with each arterial pulse. Action potentials triggered in the baroreceptor ending are then conducted to the brainstem where central terminations (synapses) transmit this information to neurons within the solitary nucleus
. Reflex responses from such baroreceptor activity can trigger increases or decreases in the heart rate. Arterial baroreceptor sensory endings are simple, sprayed nerve endings that lie in the tunica adventitia of the artery. An increase in the mean arterial pressure increases depolarization
of these sensory endings, which results in action potentials. These action potentials are conducted to the solitary nucleus in the central nervous system by axons and have a reflex effect on the cardiovascular system through autonomic
neurons. Hormone
secretions that target the heart and blood vessels are affected by the stimulation of baroreceptors.
At normal resting blood pressures, baroreceptors discharge with each heart beat. If blood pressure falls, such as on orthostatic hypotension or in hypovolaemic shock, baroreceptor firing rate decreases and baroreceptor reflexes act to help restore blood pressure by increasing heart rate. Signals from the carotid baroreceptors are sent via the glossopharyngeal nerve
(cranial nerve
IX). Signals from the aortic baroreceptors travel through the vagus nerve
(cranial nerve X
). Arterial baroreceptors inform reflexes about arterial blood pressure but other stretch receptors in the large veins and right atrium convey information about the low pressure parts of the circulatory system.
Baroreceptors respond very quickly to maintain a stable blood pressure, but their responses diminish with time and thus are most effective for conveying short term changes in blood pressure. In people with essential hypertension
the baroreceptors and their reflexes change and function to maintain the elevated blood pressure as if normal. The receptors then become less sensitive to change.
s, in pulmonary vessels, and in the walls of the right atrium and ventricles of the heart
. The low-pressure baroreceptors are involved with the regulation of blood volume. The blood volume determines the mean pressure throughout the system, in particular in the venous side where most of the blood is held.
The low-pressure baroreceptors have both circulatory and renal effects; they produce changes in hormone
secretion, resulting in profound effects on the retention of salt and water
; they also influence intake of salt and water. The renal effects allow the receptors to change the mean pressure in the system in the long term.
Denervating these receptors 'fools' the body into thinking that it has too low blood volume and initiates mechanisms that retain fluid and so push up the blood pressure to a higher level than it would otherwise have.
Mechanoreceptor
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...
that detects the pressure of blood flowing through them, and can send messages to the central nervous system
Central nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...
to increase or decrease total peripheral resistance
Total peripheral resistance
Vasculature throughout the entire body can be thought of as two separate circuits - one is the systemic circulation, while the other is the pulmonary circulation. Total peripheral resistance is the sum of the resistance of all peripheral vasculature in the systemic circulation...
and cardiac output
Cardiac output
Cardiac output is the volume of blood being pumped by the heart, in particular by a left or right ventricle in the time interval of one minute. CO may be measured in many ways, for example dm3/min...
. Baroreceptors act immediately as part of a negative feedback
Negative feedback
Negative feedback occurs when the output of a system acts to oppose changes to the input of the system, with the result that the changes are attenuated. If the overall feedback of the system is negative, then the system will tend to be stable.- Overview :...
system called the baroreflex
Baroreflex
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 heart rate to decrease therefore causing blood pressure to decrease; likewise, decreased...
, as soon as there is a change from the usual mean arterial blood pressure
Mean arterial pressure
The mean arterial pressure is a term used in medicine to describe an average blood pressure in an individual. It is defined as the average arterial pressure during a single cardiac cycle.-Calculation:...
, returning the pressure to a normal level. They are an example of a short-term blood pressure regulation mechanism. Baroreceptors detect the amount of stretch of the blood vessel walls, and send the signal to the nervous system in response to this stretch. The nucleus tractus solitarius in the medulla oblongata
Medulla oblongata
The medulla oblongata is the lower half of the brainstem. In discussions of neurology and similar contexts where no ambiguity will result, it is often referred to as simply the medulla...
recognizes changes in the firing rate of action potential
Action potential
In physiology, an action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and...
s from the baroreceptors, and influences cardiac output and systemic vascular resistance through changes in the autonomic nervous system
Autonomic nervous system
The autonomic nervous system is the part of the peripheral nervous system that acts as a control system functioning largely below the level of consciousness, and controls visceral functions. The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils,...
.
Baroreceptors can be divided into two categories: high-pressure arterial baroreceptors and low-pressure baroreceptors (also known as cardiopulmonary or volume receptors).
Arterial (high-pressure) baroreceptors
Arterial baroreceptors are located in the tranverse aortic arch and the carotid sinusCarotid sinus
In human anatomy, the carotid sinus is a localized dilation of the internal carotid artery at its origin, the common carotid artery.-Functions:...
es of the left and right internal carotid arteries. The baroreceptors found within the aortic arch monitor the pressure of blood delivered to the systemic circuit, and the baroreceptors within the carotid arteries monitor the pressure of the blood being delivered to the brain.
Arterial baroreceptors are stretch receptors that are stimulated by distortion of the arterial wall when pressure changes. The baroreceptors can identify the changes in both the average blood pressure or the rate of change in pressure with each arterial pulse. Action potentials triggered in the baroreceptor ending are then conducted to the brainstem where central terminations (synapses) transmit this information to neurons within the solitary nucleus
Solitary nucleus
The solitary tract and nucleus are structures in the brainstem that carry and receive visceral sensation and taste from the facial , glossopharyngeal and vagus cranial nerves.-Anatomy:...
. Reflex responses from such baroreceptor activity can trigger increases or decreases in the heart rate. Arterial baroreceptor sensory endings are simple, sprayed nerve endings that lie in the tunica adventitia of the artery. An increase in the mean arterial pressure increases depolarization
Depolarization
In biology, depolarization is a change in a cell's membrane potential, making it more positive, or less negative. In neurons and some other cells, a large enough depolarization may result in an action potential...
of these sensory endings, which results in action potentials. These action potentials are conducted to the solitary nucleus in the central nervous system by axons and have a reflex effect on the cardiovascular system through autonomic
Autonomic nervous system
The autonomic nervous system is the part of the peripheral nervous system that acts as a control system functioning largely below the level of consciousness, and controls visceral functions. The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils,...
neurons. Hormone
Hormone
A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...
secretions that target the heart and blood vessels are affected by the stimulation of baroreceptors.
At normal resting blood pressures, baroreceptors discharge with each heart beat. If blood pressure falls, such as on orthostatic hypotension or in hypovolaemic shock, baroreceptor firing rate decreases and baroreceptor reflexes act to help restore blood pressure by increasing heart rate. Signals from the carotid baroreceptors are sent via the glossopharyngeal nerve
Glossopharyngeal nerve
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 to the vagus nerve...
(cranial nerve
Glossopharyngeal nerve
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 to the vagus nerve...
IX). Signals from the aortic baroreceptors travel through the vagus nerve
Vagus nerve
The vagus nerve , also called pneumogastric nerve or cranial nerve X, is the tenth of twelve paired cranial nerves...
(cranial nerve X
Vagus nerve
The vagus nerve , also called pneumogastric nerve or cranial nerve X, is the tenth of twelve paired cranial nerves...
). Arterial baroreceptors inform reflexes about arterial blood pressure but other stretch receptors in the large veins and right atrium convey information about the low pressure parts of the circulatory system.
Baroreceptors respond very quickly to maintain a stable blood pressure, but their responses diminish with time and thus are most effective for conveying short term changes in blood pressure. In people with essential hypertension
Essential hypertension
Essential hypertension is the form of hypertension that by definition, has no identifiable cause. It is the most common type of hypertension, affecting 95% of hypertensive patients, it tends to be familial and is likely to be the consequence of an interaction between environmental and genetic...
the baroreceptors and their reflexes change and function to maintain the elevated blood pressure as if normal. The receptors then become less sensitive to change.
Low-pressure baroreceptors
The low-pressure baroreceptors, are found in large systemic veinVein
In the circulatory system, veins are blood vessels that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated blood to the heart...
s, in pulmonary vessels, and in the walls of the right atrium and ventricles of the heart
Heart
The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...
. The low-pressure baroreceptors are involved with the regulation of blood volume. The blood volume determines the mean pressure throughout the system, in particular in the venous side where most of the blood is held.
The low-pressure baroreceptors have both circulatory and renal effects; they produce changes in hormone
Hormone
A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...
secretion, resulting in profound effects on the retention of salt and water
Osmoregulation
Osmoregulation is the active regulation of the osmotic pressure of an organism's fluids to maintain the homeostasis of the organism's water content; that is it keeps the organism's fluids from becoming too diluted or too concentrated. Osmotic pressure is a measure of the tendency of water to move...
; they also influence intake of salt and water. The renal effects allow the receptors to change the mean pressure in the system in the long term.
Denervating these receptors 'fools' the body into thinking that it has too low blood volume and initiates mechanisms that retain fluid and so push up the blood pressure to a higher level than it would otherwise have.