Baroreceptor Reflex

In order for blood pressure to be maintained within limits, specialized receptors for pressure are needed. These baroreceptors are stretch receptors located in the aortic arch and in the carotid sinuses. An increase in pressure causes the walls of these arterial regions to stretch, increasing the frequency of action potentials along sensory nerve fibers (fig. 14.25). A fall in pressure below the normal range, by contrast, causes a decrease in the frequency of action potentials produced by these sensory nerve fibers.

Cardiac Output, Blood Flow, and Blood Pressure

Cerebrum -

Hypothalamus

Medulla oblongata

Common carotid artery

Arch of aorta

Common carotid artery

Arch of aorta

Cerebrum -

Hypothalamus

Medulla oblongata

Baroreceptor Reflex

AV node

Sympathetic cardiac nerve

Sympathetic chain

AV node

Sympathetic cardiac nerve

Sympathetic chain

■ Figure 14.26 Structures involved in the baroreceptor reflex. Sensory stimuli from baroreceptors in the carotid sinus and the aortic arch, acting via control centers in the medulla oblongata, affect the activity of sympathetic and parasympathetic nerve fibers in the heart.

Sensory nerve activity from the baroreceptors ascends, via the vagus and glossopharyngeal nerves, to the medulla oblon-gata, which directs the autonomic system to respond appropriately. The vasomotor control centers in the medulla controls vasoconstriction/vasodilation, and hence helps to regulate total peripheral resistance. The cardiac control centers in the medulla regulates the cardiac rate (fig. 14.26). Acting through the activity of motor fibers within the vagus and sympathetic nerves controlled by these brain centers, the baroreceptors function to counteract blood pressure changes so that fluctuations in pressure are minimized.

The baroreceptor reflex is activated whenever blood pressure increases or decreases. The reflex is somewhat more sensitive to decreases in pressure than to increases, and is more sensitive to sudden changes in pressure than to more gradual changes. A good example of the importance of the baroreceptor reflex in normal physiology is its activation whenever a person goes from a lying to a standing position.

When a person goes from a lying to a standing position, there is a shift of 500 to 700 ml of blood from the veins of the thoracic cavity to veins in the lower extremities, which expand to contain the extra volume of blood. This pooling of blood in the lower extremities reduces the venous return and cardiac output, but the resulting fall in blood pressure is almost immediately compensated for by the baroreceptor reflex. A decrease in baroreceptor sensory information, traveling in the glossopharyngeal nerve (IX) and the vagus nerve (X) to the medulla oblongata, inhibits parasympa thetic activity and promotes sympathetic nerve activity. This produces an increase in cardiac rate and vasoconstriction, which help to maintain an adequate blood pressure upon standing (fig. 14.27).

Clinical Investigation Clue

Remember that Charlie had low blood pressure, a rapid pulse, and cold skin.

■ How can knowledge of the baroreceptor reflex be used to understand the relationships among these observations?

Input from baroreceptors can also mediate the opposite response. When the blood pressure rises above an individual's normal range, the baroreceptor reflex causes a slowing of the cardiac rate and vasodilation. Manual massage of the carotid sinus, a procedure sometimes employed by physicians to reduce tachycardia and lower blood pressure, also evokes this reflex. Such carotid massage should be used cautiously, however, because the intense vagus-nerve-induced slowing of the cardiac rate could cause loss of consciousness (as occurs in emotional fainting). Manual massage of both carotid sinuses simultaneously can even cause cardiac arrest in susceptible people.

432 Chapter Fourteen

Going from lying — to standing position

J End-diastolic volume

\ Stroke volume

J Cardiac

J Cardiac

Baroreceptor Negative Feedback Loop

Vasoconstriction t Cardiac of arterioles rate f Sympathetic J Parasympathetic

Vasoconstriction t Cardiac of arterioles rate

Total peripheral resistance

[ Cardiac output

Negative feedback response

t Blood p

ressure

■ Figure 14.27 The negative feedback control of blood pressure by the baroreceptor reflex. This reflex helps to maintain an adequate blood pressure upon standing.

Since the baroreceptor reflex may require a few seconds before it is fully effective, many people feel dizzy jj and disoriented if they stand up too quickly. If the baroreceptor sensitivity is abnormally reduced, perhaps by atherosclerosis, an uncompensated fall in pressure may occur upon standing. This condition—called postural, or orthostatic, hypotension (hypotension = low blood pressure)—can make a person feel extremely dizzy or even faint because of inadequate perfusion of the brain.

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Responses

  • Warren
    Where are the sympathetic cardiac nerve?
    7 years ago
  • PRIMA
    What are the baroreceptors reflex response to low blood pressure?
    7 years ago
  • Fidenzio Costa
    How does the baroreceptor reflex helps to compensate for a fall in blood pressure?
    7 years ago
  • ulrich
    Does medulla oblongata control peripheral resistance?
    7 years ago
  • juliane
    Why does decreased blood pressure cause baroreceptor reflex?
    7 years ago
  • togo
    How to massage baroreceptors during bp?
    7 years ago
  • Katelyn
    Is carotid massage a vasoreceptor?
    7 years ago
  • joseph
    Why does low blood pressure cause baroreceptor reflex and an increase in ventilation?
    7 years ago
  • Glenn
    What nerve goes from the medulla oblongata to the heart?
    7 years ago
  • bellisima
    What is the position barorecptors when standing?
    7 years ago
  • omar
    Why does a person with normal blood pressure lose consciousness when the baroreceptor refle is?
    7 years ago
  • Saba
    How does baroreceptor reflex regulate blood pressure?
    7 years ago
  • YOHANNES
    What is low blood pressure physiology?
    7 years ago
  • armando
    Does carotid massage raise or lower bp?
    7 years ago
  • Awet
    Where are the baroreceptors located in the human body >?
    7 years ago
  • NIKLAS THEISSEN
    How baroreceptors increases blood pressure?
    7 years ago
  • Jeffery Vine
    Why would a person lose consciousness with normal blood pressure with the baroreceptor relflex?
    7 years ago
  • cora
    How heart rate changes with exercise. Include the roles of the blood, medulla, nerves and SA node.?
    7 years ago
  • Gabriel
    When blood pressure rises the baro receptors?
    7 years ago
  • Alyssa
    What is the stimulus for baroreceptor reflex?
    7 years ago
  • bell goodbody
    Why are the carotid sinus and aortic arch important sites for baroreceptors?
    7 years ago
  • semere
    How is the freq of action potential change when someone goes from lying to standing?
    7 years ago
  • pamela
    How medulla oblongata maintain blood pressure?
    7 years ago
  • lucas
    Where are baroreceptor reflex located?
    7 years ago
  • MAC BROWN
    How to test baroreceptor reflex?
    7 years ago
  • katrin
    How baroreceptors activated by low blood pressure?
    7 years ago
  • Patrick
    What is the average person's baroreceptor reflex?
    7 years ago
  • Ute
    When the baroreceptor reflex is activated in response to low blood pressure?
    7 years ago
  • PEREGRIN
    What will happen to blood pressure when standing for awhile due to baroreceptor reflex?
    7 years ago
  • Franciszek
    What control center is activated by action potentials from the baroreceptors?
    7 years ago
  • VIHTORI ROVANPER
    When a person rises quickly from a lying position carotid baroreceptors?
    7 years ago
  • Mary
    How the baroreceptor response when standing up?
    7 years ago
  • Christina Mackenzie
    WHICH NERVE IN THE Medulla Oblongata CONTROLS COUGHING?
    7 years ago
  • lalia brockhouse
    Why do people lose conciousness in a baroreceptor reflex?
    7 years ago
  • osman
    What is the response of the barorecptor reflex when blood pressure increases and decreases?
    7 years ago
  • Dinodas T
    What regulate spinal reflexes?
    7 years ago
  • Hunter
    How does the baroreceptor reflex control changes in bp from lying to standing?
    6 years ago
  • ghenet efrem
    What is the stimulus for the baroceptor reflex?
    6 years ago
  • shukornia
    Where are the stretch receptors for the baroreceptor reflex located?
    6 years ago
  • marina freeh
    Why baroreceptors cause hypotension?
    6 years ago
  • asmara
    What causes the baroreceptor reflex in response to increased blood pressure?
    6 years ago
  • Gioacchina Cocci
    Why does a person lose consciousness during baroreceptor reflex?
    6 years ago
  • Marko
    Why does baroreceptor reflex cause fainting?
    6 years ago
  • MELANIE
    Why would a person lose consciousness in barnirecepter?
    6 years ago
  • kaarlo
    How baroreceptors affect cardiac output?
    6 years ago
  • Venanzio
    What happens with an increse in the frequency of action potentials produced by the baroreceptors?
    6 years ago
  • Lawrence
    What is the effect of the barorecptor reflex on normal blood pressure loss of consciousness?
    6 years ago
  • Vivaldo Romano
    How does the baroreceptor reflex help to maintain blood pressure?
    6 years ago
  • dominik
    How does the baroreceptor reflex help in the maintenance of systemic blood pressure?
    6 years ago
  • asfaha
    What is the advantage to a baroreceptor reflex and increased ventilation?
    6 years ago
  • hagos
    How does baroreceptors compensate for fall in blodd pressure?
    6 years ago
  • isengrin
    What happens to a person when the baroreceptor reflexs are slow?
    6 years ago
  • Aleksi
    Does the carotoid sinus reflex help regulate heart rate?
    6 years ago
  • j
    What is an advantage of a baroreceptor reflex that leads to increased ventilation?
    6 years ago
  • caden
    What is the stimulus for varoreceptor reflex?
    6 years ago
  • milen
    When baroreceptors sense a change in pressure autonomic?
    6 years ago
  • jyrki
    How does cardiovascular control center respond to baroreceptors?
    6 years ago
  • Manuela Junker
    Does the baroreceptor reflex involve the hypothalamus?
    6 years ago
  • LEILA
    Why does baroreceptor reflex cause loss of consciousness?
    6 years ago
  • PIERA LUCCHESI
    What is barrel reflex?
    6 years ago
  • kaija
    What is the advantage of increased ventilation from baroreceptors?
    6 years ago
  • andreas
    What would not happen if baroreceptors in the carotid and aortic sinuses were inhibited?
    6 years ago
  • Aloisia
    What is a normal baroreceptor in humans?
    6 years ago
  • mezan
    When baroreceptors sense a change in pressure, the autonomic nervous system is activated?
    6 years ago
  • Abrha Aziz
    Why would compression of the common carotid artery cause a person to lose consciousness?
    5 years ago
  • leena kangas
    How does the baroreceptor reflex control changes in blood pressure from lying down to standing?
    5 years ago
  • Ruth
    How does baroreceptor reflex affect sodium balance?
    5 years ago
  • Asfaha
    How does the baroreceptor reflex react during anaphalysis?
    5 years ago
  • VENERANDO
    Why would compression of the common caratid arteries cause a person to lose consciousness?
    5 years ago
  • BORIS
    What are the receptors involved in the reflex control of blood pressure?
    5 years ago
  • louis duncan
    What advantage baroreceptor in aortic?
    4 years ago
  • Cheryl
    Where are the stretch receptors for baroreceptors located?
    4 years ago
  • stefan
    How does baroreceptor reflex affect blood pressure?
    4 years ago
  • felix
    What happens to baroreceptors when laying down?
    4 years ago
  • wiseman
    How is blood pressure maintained baroreceptors?
    4 years ago
  • vilma
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    4 years ago
  • Lily
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    3 years ago
  • LOTHO
    Do baroreceptors increase activity if go from standng up to lyring down?
    3 years ago
  • lemlem
    How would a baroreceptor respond to someone laying down?
    3 years ago
  • ELSA
    How does carotid massage lower the blood pressure?
    3 years ago
  • abeba
    How does sinus affects the medulla oblongata?
    3 years ago
  • wegahta
    How does the baroreceptor reflex help to compesate falling blood pressure?
    3 years ago
  • Camelia
    What happens when baroreceptors are stretched less?
    2 years ago
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    What can baroreceptors affect when they are activated?
    2 years ago
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    2 years ago
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    2 years ago
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    What will happen in manual stimulation of baroreceptor in carotid artery?
    2 years ago
  • Federica
    How cold skin and rapid pulse are related to baroreceptor reflex?
    2 years ago
  • Paul
    How the baroreceptor reflex control orthostatic hypotension?
    2 years ago
  • conlan
    How is blood prssure maintained by barorcepteor feedback mechanism?
    1 year ago
  • Angelika
    Which system regulates blood pressure through baroreceptor reflexes?
    1 year ago
  • Jacob
    How baroreceptor reflex arc regulates normal blood pressure?
    1 year ago
  • mhret
    How does reflex control influence blood flow?
    11 months ago
  • lisa
    How does the baroreceptor reflex help to compensate for a falling blood pressure?
    10 months ago
  • ermias
    What happened when manual stimulation of baroreceptor in carotid sinus?
    8 months ago
  • NOORA
    What are the results of increased baroreceptor response?
    8 months ago
  • yolanda
    How does baroreflex detect immediate pressure change after lying down?
    6 months ago
  • sol
    Where are the sensors for the arterial baroreceptor reflex located?
    6 months ago
  • Julie Yip
    How does the body respond to correct hypotension?
    6 months ago
  • selam
    Which cells are involved in baroreceptor reflex?
    5 months ago
  • Gerard
    How does the baroreceptor reflex work in cells?
    5 months ago
  • berhane
    What do baroreceptors trigger?
    4 months ago
  • Affiano Lucchesi
    Is blud involved in reflexs?
    2 months ago
  • tullia
    Does standing rduce baroreceptor stimulation?
    2 months ago
  • Estella
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    2 months ago
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    What does the baroreceptor reflex do when blood pressure goes donw?
    2 months ago
  • licia
    How does the baroreceptor reflex affect peripheral resistance?
    2 months ago
  • RUSSOM
    Do baroreceptors in the aorta and carotid lower bp with the vagus and glossopharyngeal nerves?
    1 month ago
  • marian
    How the baroreflex detects the immediate pressure change after lying down?
    1 month ago
  • guido
    How do baroreceptors compensate for decreased perfusion?
    27 days ago
  • conlan
    What is a good response to baroreceptor reflexes?
    11 days ago

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