Autonomic Control of Blood Pressure

Question 1

What is the equation for MAP?

Answer 1

CO X TPR

Question 2

What are the three ways that MAP is monitored?

Answer 2

1- High pressure baroreceptors

2- Renal juxtaglomerular apparatus

3- Low-pressure baroreceptors

Question 3

Where are High pressure baroreceptors typically found?

Answer 3

the arterial side of circulation

Question 4

Where are low pressure baroreceptors typically found?

Answer 4

the venous side of circulation

Question 5

What is the single most import mechanism providing short term regulation of arterial pressure?

Answer 5

High pressure baroreceptor reflex

Question 6

What are two major locations of arterial (high pressure) baroreceptors?

Answer 6

1- carotid sinus

2- aortic arch

Question 7

An increase in the arterial pressure stretches the baroreceptors and causes the baroreceptors to do what?

Answer 7

It causes them to transmit more AP to the CNS medullary control center. “Feedback” signals are then sent back through the ANS to the circulation to reduce arterial pressure

Question 8

How are signals from the “carotid baroreceptors” in the carotid sinus transmitted?

Answer 8

Submitted through small Hering’s nerves to glossopharyngeal nerves (IX) in the high neck, and then to the nucleus tractus solitarius (NTS)

Question 9

Where is the nucleus tractus solitarius (NTS) located?

Answer 9

In the medulla

Question 10

How are signals from the “aortic baroreceptors” in the aortic arch transmitted?

Answer 10

Through vagus (X) to the NTS in the medulla

Question 11

At what arterial pressure is the chemoreceptor reflex a powerful arterial pressure controller?

Answer 11

When arterial pressure falls below 80 mmHg

at lower pressures this reflex becomes important to help prevent further decreases in arterial pressures

Question 12

Where are central chemoreceptors located?

Answer 12

in the medulla

Question 13

What are central chemoreceptors sensitive to?

Answer 13

They are sensitive to decreases in brain pH (which reflects an increase in arterial PCO2)

Question 14

What two factors work together to enhance vasoconstriction?

Answer 14

A low Po2 acting on peripheral chemoreceptors and a high PCO2 acting on the central chemoreceptor

Question 15

Where are peripheral chemoreceptors located?

Answer 15

in the carotid and aortic bodies

they are in close contact with arterial blood

Question 16

What are the baroreceptors in the carotid sinus and aortic arch?

Answer 16

They are branched terminals of myelinated and unmyelinated sensory nerve fibers. They are intermeshed within the elastic layers

Question 17

What does an increase in transmural pressure difference cause?

Answer 17

1- enlarges the vessel
2- deforms the receptors
3- increases firing rate of the baroreceptor’s sensory nerve

Question 18

Do baroreceptors increase or decrease their rate of firing in response to stretch (increased MAP)?

Answer 18

They increase their rate in a frequency dependent manner

Question 19

Describe the increase in frequency of APs in response to stretch?

Answer 19

Following a large initial depolarization (the dynamic component) is a more modest but steady depolarization (the static component)

Basically, after the initial burst, it settles into a patter that is reflective of the pressure step

Question 20

Do baroreceptors respond slowly or rapidly to changes in arterial pressure?

Answer 20

They respond rapidly to changes

Question 21

Within what range are baroreceptors most sensitive?

Answer 21

They are most sensitive in the normal operating range (about 100 mmHg for Carotid sinus baroreceptors and about 130 mmHg for aortic arch baroreceptors)

Question 22

Are carotid sinus baroreceptrs stimilated by pressures between 1 and 60 mm Hg?

Answer 22

No they do not

Question 23

If there are no baroreceptors, what is the effect on MAP?

Answer 23

It fluctuates a lot

Question 24

What types of blood vessels does the sympathetic nervous system innervate?

Answer 24

All except the capillaries

Question 25

Sympathetic innervation of small arteries and arterioles allows for what?

Answer 25

increase resistance to blood flow, and a decreased rate of blood flow through the tissues

Question 26

Sympathetic innervation of large vessels allows for what?

Answer 26

decrease the volume of the vessels…they push blood into the heart and thereby play a major role in regulation of cardiac output

Question 27

What is vasomotor tone?

Answer 27

The partial state of contraction in blood vessels

Question 28

When you inhibit SNS, what is the effect on the vasomotor tone?

Answer 28

It is lost, which corresponds with a marked decrease in MAP

Question 29

Explain what happens when there is an increase in MAP

Answer 29

1- baroreceptros are stretched and activated

2- increased firing of baroreceptors that sends signal through the afferent pathway

3- the coordinating center in the medulla receives the message and sends signal back to restore MAP to set point

4- response signal is sent via efferent pathway to effectors in tissue

5- Bradycardia and vasodilation counteract increased MAP

Question 30

Can baroreceptor reflex adapt to long-term changes in MAP?

Answer 30

yes– for example in hypertension, the set point is raised

Question 31

What type of change in made by the baroreceptor reflex when changing posture from a standing to a lying posion?

Answer 31

This position change leads to a reflex to decrease MAP

Question 32

Does the vagus have any effect on blood vessels or the heart?

Answer 32

The heart, but not vessels

Question 33

A change in posture from standing to lying down increases venous return and has what effect on stroke volume and MAP?

Answer 33

It inceases SV and increases MAP

Question 34

What does carotid sinus massage achieve?

Answer 34

Stimulates baroreceptros and reflexly slows the heart in people with atrial tachycardia

Question 35

When going from supine to standing position, the MAP…..

Answer 35

decreases

Question 36

What can be used to test the integrity of the baroreceptor reflex?

Answer 36

The valsalva maneuver

Question 37

What is the valsalva maneuver?

Answer 37

Subject is asked to expire against a closed glottis which increases the intrathoracic pressure and a decrease in venous return to the heart which causes decrease in CO and MAP

Intact baroreceptors will sense the decrease in MAP and direct an increase in SNS and decrease in PNS outflow to the heart and vessels, the increase in HR is measured

A rebound decrease in HR is noted after release from the maneuver

Question 38

How are the SNS and the PNS controlled?

Answer 38

The are under reciprocal control