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The Baroreceptors are in the carotid sinus (glossopharyngeal n.) and aortic arch (vagus n.) PowerPoint PPT Presentation

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In the power company they keep the voltage in your house constant (110 V) and you vary the resistance of what you plug in to determine how much power you want to use. .

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The Baroreceptors are in the carotid sinus (glossopharyngeal n.) and aortic arch (vagus n.)

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In the power company they keep the voltage in your house constant (110 V) and you vary the resistance of what you plug in to determine how much power you want to use.

The body works the same way. 100 mmHg is maintained in the aorta and autoregulation controls blood flow in each organ in the periphery.

Overall aim of the system is to keep aortic pressure constant and let the organs regulate their own flow through autoregulation.

Sympathetic nerves: Spinal cord to sympathetic chain. Innervate heart (increase rate and force), cause adrenal gland to secrete both epinephrine and norepinephrine. They innervate peripheral vessels and are constrictor. sympathetic nerves are tonic.

Parasympathetic nerves: Vagus n. only. Go to the heart’s atria and the viscera.

Peripheral vasodilation or decreases in contractility must be done by withdrawing sympathetic tone.

The vasomotor center in the brainstem receives input from hypothalamus, cranial nerves and higher centers.

The Baroreceptors are in the carotid sinus (glossopharyngeal n.) and aortic arch (vagus n.)

A. Rate of discharge increases with blood pressure.

B. Afferent activity inhibits sympathetics and activates parasympathetics.

C. Negative feedback results in moment-to-moment arterial pressure control.

D. The system is designed so that 100 mmHg is maintained in the arterial system. Each organ adjusts its resistance (autoregulation) so that its nutritional needs are met.

E. Only pressure is regulated. There is no cardiac output sensor.

carotid sinus nerve (afferent)

vagus nerve (efferent)

cardiac sympathetic nerves

sympathetic constrictor nerves

  • Blood pressure control is based on negative feedback.

  • Negative feedback requires a:

  • Detector

  • Integrator

  • set point

  • effector

Your furnace

carotid sinuses & aortic arch

  • Detector

  • Integrator

  • set point

  • effector

Heart & Per. Res.


100 mmHg

Your body

  • Autoregulation always has priority over sympathetic constriction. Only those vessels not participating in an active hyperemia will constrict.

  • That includes renal, non-exercising skeletal muscle, skin, and non-digesting intestine.

Why does clamping carotid arteries raise the blood pressure?

Why would cutting the vagus nerve exaggerate the response?

The baroreflex only acts to control minute-to-minute blood pressure.

Blood pressure changes due to:

Active hyperemia

Hydrostatic columns

Note that mean pressure is not changed by denervation.

The long-term control of blood pressure is controlled by blood volume

  • The sequence of events with exercise will be:

  • An active hyperemia in the exercising muscles,

  • A drop in peripheral resistance and thus blood pressure.

  • Detected by the baroreceptors

  • Initiate a reflex to move pressure back toward the set point

In heavy exercise blood pressure will actually increase. That is because the CNS increases the set point during heavy exercise to deliver more flow to the periphery.

Peripheral chemoreceptors Primarily control pulmonary function but their effects spill over into the CV system

Carotid and Aortic Bodies

The Cushing’s reflex: Cerebral ischemia causes a massive discharge of both sympathetic and parasympathetic nerves. The net result is hypertension with bradycardia.

Seen in head trauma with intracranial bleed.

The vagus is dominant over the sympathetics at the SA node

Low-pressure receptors in lung and atria accommodate sudden changes in blood volume.

  • Increase the heart rate (Bainbridge reflex)

  • Decrease sympathetic tone to the kidney causing increased filtration and urine formation.

  • Decrease production of vasopressin (anti-diuretic hormone)

  • Atrial stretch also causes the atria to make atrial natriuretic peptide (ANP)

    These effects act to lower blood volume

  • The Long-term regulation of blood pressure is done by regulating blood volume.

Venous pressure is a major determinant of cardiac output in both ventricles.

Blood volume determines venous pressure.

At the same time cardiac output determines arterial pressure


The blood pressure then adjusts to maintain a balance between salt intake and loss



Because the curve is very steep a large increase in salt intake causes only a small increase in arterial pressure

The rate at which the kidney loses sodium is determined by the blood pressure

Loss curve

VI. Long-term blood pressure control is at the Kidney.

Hypertension can result from a failure of the kidney to regulate blood volume.

Either the set point can be raised e.g. occurs in renal artery stenosis

or the gain of the system can be decreased as occurs in loss of renal mass.

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